variable.c (293c4f9246239937ca460c9dc64639fc5180e74e)

/**********************************************************************
 
  variable.c -
 
  $Author$
  created at: Tue Apr 19 23:55:15 JST 1994
 
  Copyright (C) 1993-2007 Yukihiro Matsumoto
  Copyright (C) 2000  Network Applied Communication Laboratory, Inc.
  Copyright (C) 2000  Information-technology Promotion Agency, Japan
 
**********************************************************************/
 
#include "ruby/internal/config.h"
#include <stddef.h>
#include "ruby/internal/stdbool.h"
#include "ccan/list/list.h"
#include "constant.h"
#include "debug_counter.h"
#include "id.h"
#include "id_table.h"
#include "internal.h"
#include "internal/box.h"
#include "internal/class.h"
#include "internal/compilers.h"
#include "internal/error.h"
#include "internal/eval.h"
#include "eval_intern.h"
#include "internal/hash.h"
#include "internal/object.h"
#include "internal/gc.h"
#include "internal/ractor.h"
#include "internal/re.h"
#include "internal/string.h"
#include "internal/struct.h"
#include "internal/symbol.h"
#include "internal/thread.h"
#include "internal/variable.h"
#include "internal/vm.h"
#include "ruby/encoding.h"
#include "ruby/st.h"
#include "ruby/util.h"
#include "shape.h"
#include "symbol.h"
#include "variable.h"
#include "vm_core.h"
#include "ractor_core.h"
#include "vm_sync.h"
 
RUBY_EXTERN rb_serial_t ruby_vm_global_cvar_state;
#define GET_GLOBAL_CVAR_STATE() (ruby_vm_global_cvar_state)
 
typedef void rb_gvar_compact_t(void *var);
 
static struct rb_id_table *rb_global_tbl;
 
// This hash table maps file paths to loadable features. We use this to track
// autoload state until it's no longer needed.
// feature (file path) => struct autoload_data
static VALUE autoload_features;
 
// This mutex is used to protect autoloading state. We use a global mutex which
// is held until a per-feature mutex can be created. This ensures there are no
// race conditions relating to autoload state.
static VALUE autoload_mutex;
 
static void check_before_mod_set(VALUE, ID, VALUE, const char *);
static void setup_const_entry(rb_const_entry_t *, VALUE, VALUE, rb_const_flag_t);
static VALUE rb_const_search(VALUE klass, ID id, int exclude, int recurse, int visibility, VALUE *found_in);
static st_table *generic_fields_tbl_;
 
/* Mutex guarding the single global generic_fields table (all hosts, every Ractor).  A
 * dedicated mutex (vm->ractor.generic_fields_lock) because a local GC's marking reads
 * the table and must not wait for the VM lock: joining a barrier mid-mark would expose
 * a half-collected heap.  The global GC's weak pass cleans the table under the barrier,
 * lock-free.  Sections that may allocate disable GC first: no self-re-entry. */
 
typedef int rb_ivar_foreach_callback_func(ID key, VALUE val, st_data_t arg);
static void rb_field_foreach(VALUE obj, rb_ivar_foreach_callback_func *func, st_data_t arg, bool ivar_only);
 
void
rb_generic_fields_lock_atfork(void)
{
    /* Another thread may have held it at fork time, so rebuild it in the child. */
    rb_native_mutex_initialize(&GET_VM()->ractor.generic_fields_lock);
}
 
void
Init_var_tables(void)
{
    rb_global_tbl = rb_id_table_create(0);
    generic_fields_tbl_ = st_init_numtable();
 
    autoload_mutex = rb_mutex_new();
    rb_obj_hide(autoload_mutex);
    rb_vm_register_global_object(autoload_mutex);
 
    autoload_features = rb_ident_hash_new();
    rb_obj_hide(autoload_features);
    rb_vm_register_global_object(autoload_features);
}
 
static inline bool
rb_namespace_p(VALUE obj)
{
    if (RB_SPECIAL_CONST_P(obj)) return false;
    switch (RB_BUILTIN_TYPE(obj)) {
      case T_MODULE: case T_CLASS: return true;
      default: break;
    }
    return false;
}
 
static VALUE
classname(VALUE klass, bool *permanent)
{
    *permanent = false;
 
    VALUE classpath = RCLASS_CLASSPATH(klass);
    if (classpath == 0) return Qnil;
 
    *permanent = RCLASS_PERMANENT_CLASSPATH_P(klass);
 
    return classpath;
}
 
VALUE
rb_mod_name0(VALUE klass, bool *permanent)
{
    return classname(klass, permanent);
}
 
/*
 *  call-seq:
 *     mod.name    -> string or nil
 *
 *  Returns the name of the module <i>mod</i>.  Returns +nil+ for anonymous modules.
 */
 
VALUE
rb_mod_name(VALUE mod)
{
    // YJIT needs this function to not allocate.
    bool permanent;
    return classname(mod, &permanent);
}
 
// Similar to logic in rb_mod_const_get().
static bool
is_constant_path(VALUE name)
{
    const char *path = RSTRING_PTR(name);
    const char *pend = RSTRING_END(name);
    rb_encoding *enc = rb_enc_get(name);
 
    const char *p = path;
 
    if (p >= pend || !*p) {
        return false;
    }
 
    while (p < pend) {
        if (p + 2 <= pend && p[0] == ':' && p[1] == ':') {
            p += 2;
        }
 
        const char *pbeg = p;
        while (p < pend && *p != ':') p++;
 
        if (pbeg == p) return false;
 
        if (rb_enc_symname_type(pbeg, p - pbeg, enc, 0) != ID_CONST) {
            return false;
        }
    }
 
    return true;
}
 
struct sub_temporary_name_args {
    VALUE names;
    ID last;
};
 
static VALUE build_const_path(VALUE head, ID tail);
static void set_sub_temporary_name_foreach(VALUE mod, struct sub_temporary_name_args *args, VALUE name);
 
static VALUE
set_sub_temporary_name_recursive(VALUE mod, VALUE data, int recursive)
{
    if (recursive) return Qfalse;
 
    struct sub_temporary_name_args *args = (void *)data;
    VALUE name = 0;
    if (args->names) {
        name = build_const_path(rb_ary_last(0, 0, args->names), args->last);
    }
    set_sub_temporary_name_foreach(mod, args, name);
    return Qtrue;
}
 
static VALUE
set_sub_temporary_name_topmost(VALUE mod, VALUE data, int recursive)
{
    if (recursive) return Qfalse;
 
    struct sub_temporary_name_args *args = (void *)data;
    VALUE name = args->names;
    if (name) {
        args->names = rb_ary_hidden_new(0);
    }
    set_sub_temporary_name_foreach(mod, args, name);
    return Qtrue;
}
 
static enum rb_id_table_iterator_result
set_sub_temporary_name_i(ID id, VALUE val, void *data)
{
    val = ((rb_const_entry_t *)val)->value;
    if (rb_namespace_p(val) && !RCLASS_PERMANENT_CLASSPATH_P(val)) {
        VALUE arg = (VALUE)data;
        struct sub_temporary_name_args *args = data;
        args->last = id;
        rb_exec_recursive_paired(set_sub_temporary_name_recursive, val, arg, arg);
    }
    return ID_TABLE_CONTINUE;
}
 
static void
set_sub_temporary_name_foreach(VALUE mod, struct sub_temporary_name_args *args, VALUE name)
{
    RCLASS_WRITE_CLASSPATH(mod, name, FALSE);
    struct rb_id_table *tbl = RCLASS_CONST_TBL(mod);
    if (!tbl) return;
    if (!name) {
        rb_id_table_foreach(tbl, set_sub_temporary_name_i, args);
    }
    else {
        rb_len_t names_len = RARRAY_LEN(args->names); // paranoiac check?
        rb_ary_push(args->names, name);
        rb_id_table_foreach(tbl, set_sub_temporary_name_i, args);
        rb_ary_set_len(args->names, names_len);
    }
}
 
static void
set_sub_temporary_name(VALUE mod, VALUE name)
{
    struct sub_temporary_name_args args = {name};
    VALUE arg = (VALUE)&args;
    rb_exec_recursive_paired(set_sub_temporary_name_topmost, mod, arg, arg);
}
 
/*
 *  call-seq:
 *     mod.set_temporary_name(string) -> self
 *     mod.set_temporary_name(nil) -> self
 *
 *  Sets the temporary name of the module. This name is reflected in
 *  introspection of the module and the values that are related to it, such
 *  as instances, constants, and methods.
 *
 *  The name should be +nil+ or a non-empty string that is not a valid constant
 *  path (to avoid confusing between permanent and temporary names).
 *
 *  The method can be useful to distinguish dynamically generated classes and
 *  modules without assigning them to constants.
 *
 *  If the module is given a permanent name by assigning it to a constant,
 *  the temporary name is discarded. A temporary name can't be assigned to
 *  modules that have a permanent name.
 *
 *  If the given name is +nil+, the module becomes anonymous again.
 *
 *  Example:
 *
 *    m = Module.new # => #<Module:0x0000000102c68f38>
 *    m.name #=> nil
 *
 *    m.set_temporary_name("fake_name") # => fake_name
 *    m.name #=> "fake_name"
 *
 *    m.set_temporary_name(nil) # => #<Module:0x0000000102c68f38>
 *    m.name #=> nil
 *
 *    c = Class.new
 *    c.set_temporary_name("MyClass(with description)") # => MyClass(with description)
 *
 *    c.new # => #<MyClass(with description):0x0....>
 *
 *    c::M = m
 *    c::M.name #=> "MyClass(with description)::M"
 *
 *    # Assigning to a constant replaces the name with a permanent one
 *    C = c
 *
 *    C.name #=> "C"
 *    C::M.name #=> "C::M"
 *    c.new # => #<C:0x0....>
 */
 
VALUE
rb_mod_set_temporary_name(VALUE mod, VALUE name)
{
    rb_class_owner_check(mod);
 
    // We don't allow setting the name if the classpath is already permanent:
    if (RCLASS_PERMANENT_CLASSPATH_P(mod)) {
        rb_raise(rb_eRuntimeError, "can't change permanent name");
    }
 
    if (NIL_P(name)) {
        // Set the temporary classpath to NULL (anonymous):
        RB_VM_LOCKING() {
            set_sub_temporary_name(mod, 0);
        }
    }
    else {
        // Ensure the name is a string:
        StringValue(name);
 
        if (RSTRING_LEN(name) == 0) {
            rb_raise(rb_eArgError, "empty class/module name");
        }
 
        if (is_constant_path(name)) {
            rb_raise(rb_eArgError, "the temporary name must not be a constant path to avoid confusion");
        }
 
        name = rb_str_new_frozen(name);
        RB_OBJ_SET_SHAREABLE(name);
 
        // Set the temporary classpath to the given name:
        RB_VM_LOCKING() {
            set_sub_temporary_name(mod, name);
        }
    }
 
    return mod;
}
 
static VALUE
make_temporary_path(VALUE obj, VALUE klass)
{
    VALUE path;
    switch (klass) {
      case Qnil:
        path = rb_sprintf("#<Class:%p>", (void*)obj);
        break;
      case Qfalse:
        path = rb_sprintf("#<Module:%p>", (void*)obj);
        break;
      default:
        path = rb_sprintf("#<%"PRIsVALUE":%p>", klass, (void*)obj);
        break;
    }
    OBJ_FREEZE(path);
    return path;
}
 
typedef VALUE (*fallback_func)(VALUE obj, VALUE name);
 
static VALUE
rb_tmp_class_path(VALUE klass, bool *permanent, fallback_func fallback)
{
    VALUE path = classname(klass, permanent);
 
    if (!NIL_P(path)) {
        return path;
    }
 
    if (RB_TYPE_P(klass, T_MODULE)) {
        if (rb_obj_class(klass) == rb_cModule) {
            path = Qfalse;
        }
        else {
            bool perm;
            path = rb_tmp_class_path(RBASIC(klass)->klass, &perm, fallback);
        }
    }
 
    *permanent = false;
    return fallback(klass, path);
}
 
VALUE
rb_class_path(VALUE klass)
{
    bool permanent;
    VALUE path = rb_tmp_class_path(klass, &permanent, make_temporary_path);
    if (!NIL_P(path)) path = rb_str_dup(path);
    return path;
}
 
VALUE
rb_class_path_cached(VALUE klass)
{
    return rb_mod_name(klass);
}
 
static VALUE
no_fallback(VALUE obj, VALUE name)
{
    return name;
}
 
VALUE
rb_search_class_path(VALUE klass)
{
    bool permanent;
    return rb_tmp_class_path(klass, &permanent, no_fallback);
}
 
static VALUE
build_const_pathname(VALUE head, VALUE tail)
{
    VALUE path = rb_str_dup(head);
    rb_str_cat2(path, "::");
    rb_str_append(path, tail);
    return rb_fstring(path);
}
 
static VALUE
build_const_path(VALUE head, ID tail)
{
    return build_const_pathname(head, rb_id2str(tail));
}
 
void
rb_set_class_path_string(VALUE klass, VALUE under, VALUE name)
{
    bool permanent = true;
 
    VALUE str;
    if (under == rb_cObject) {
        str = rb_str_new_frozen(name);
    }
    else {
        str = rb_tmp_class_path(under, &permanent, make_temporary_path);
        str = build_const_pathname(str, name);
    }
 
    RB_OBJ_SET_SHAREABLE(str);
    RCLASS_SET_CLASSPATH(klass, str, permanent);
}
 
void
rb_set_class_path(VALUE klass, VALUE under, const char *name)
{
    VALUE str = rb_str_new2(name);
    OBJ_FREEZE(str);
    rb_set_class_path_string(klass, under, str);
}
 
VALUE
rb_path_to_class(VALUE pathname)
{
    rb_encoding *enc = rb_enc_get(pathname);
    const char *pbeg, *pend, *p, *path = RSTRING_PTR(pathname);
    ID id;
    VALUE c = rb_cObject;
 
    if (!rb_enc_asciicompat(enc)) {
        rb_raise(rb_eArgError, "invalid class path encoding (non ASCII)");
    }
    pbeg = p = path;
    pend = path + RSTRING_LEN(pathname);
    if (path == pend || path[0] == '#') {
        rb_raise(rb_eArgError, "can't retrieve anonymous class %"PRIsVALUE,
                 QUOTE(pathname));
    }
    while (p < pend) {
        while (p < pend && *p != ':') p++;
        id = rb_check_id_cstr(pbeg, p-pbeg, enc);
        if (p < pend && p[0] == ':') {
            if ((size_t)(pend - p) < 2 || p[1] != ':') goto undefined_class;
            p += 2;
            pbeg = p;
        }
        if (!id) {
            goto undefined_class;
        }
        c = rb_const_search(c, id, TRUE, FALSE, FALSE, NULL);
        if (UNDEF_P(c)) goto undefined_class;
        if (!rb_namespace_p(c)) {
            rb_raise(rb_eTypeError, "%"PRIsVALUE" does not refer to class/module",
                     pathname);
        }
    }
    RB_GC_GUARD(pathname);
 
    return c;
 
  undefined_class:
    rb_raise(rb_eArgError, "undefined class/module % "PRIsVALUE,
             rb_str_subseq(pathname, 0, p-path));
    UNREACHABLE_RETURN(Qundef);
}
 
VALUE
rb_path2class(const char *path)
{
    return rb_path_to_class(rb_str_new_cstr(path));
}
 
VALUE
rb_class_name(VALUE klass)
{
    return rb_class_path(rb_class_real(klass));
}
 
const char *
rb_class2name(VALUE klass)
{
    bool permanent;
    VALUE path = rb_tmp_class_path(rb_class_real(klass), &permanent, make_temporary_path);
    if (NIL_P(path)) return NULL;
    return RSTRING_PTR(path);
}
 
const char *
rb_obj_classname(VALUE obj)
{
    return rb_class2name(CLASS_OF(obj));
}
 
struct trace_var {
    int removed;
    void (*func)(VALUE arg, VALUE val);
    VALUE data;
    struct trace_var *next;
};
 
struct rb_global_variable {
    int counter;
    int block_trace;
    VALUE *data;
    rb_gvar_getter_t *getter;
    rb_gvar_setter_t *setter;
    rb_gvar_marker_t *marker;
    rb_gvar_compact_t *compactor;
    struct trace_var *trace;
    ID id;
    bool box_ready;
    bool box_dynamic;
};
 
struct rb_global_entry {
    struct rb_global_variable *var;
    ID id;
    bool ractor_local;
};
 
static void
free_global_variable(struct rb_global_variable *var)
{
    RUBY_ASSERT(var->counter == 0);
 
    struct trace_var *trace = var->trace;
    while (trace) {
        struct trace_var *next = trace->next;
        SIZED_FREE(trace);
        trace = next;
    }
    SIZED_FREE(var);
}
 
static enum rb_id_table_iterator_result
free_global_entry_i(VALUE val, void *arg)
{
    struct rb_global_entry *entry = (struct rb_global_entry *)val;
    entry->var->counter--;
    if (entry->var->counter == 0) {
        free_global_variable(entry->var);
    }
    SIZED_FREE(entry);
    return ID_TABLE_DELETE;
}
 
void
rb_free_rb_global_tbl(void)
{
    rb_id_table_foreach_values(rb_global_tbl, free_global_entry_i, 0);
    rb_id_table_free(rb_global_tbl);
}
 
void
rb_free_generic_fields_tbl_(void)
{
    st_free_table(generic_fields_tbl_);
}
 
static void
rb_gvar_undef_compactor(void *var)
{
}
 
NORETURN(static void global_entry_isolation_error(ID id));
 
static void
global_entry_isolation_error(ID id)
{
    rb_raise(rb_eRactorIsolationError, "can not access global variable %s from non-main Ractor", rb_id2name(id));
}
 
/* Sets *isolation_error when the caller must raise; the caller has to do that
 * once it no longer holds the VM lock. */
static struct rb_global_entry*
global_entry_lookup(ID id, bool create_entry, bool *isolation_error)
{
    struct rb_global_entry *entry;
    VALUE data;
 
    RB_VM_LOCKING() {
        if (rb_id_table_lookup(rb_global_tbl, id, &data)) {
            entry = (struct rb_global_entry *)data;
            RUBY_ASSERT(entry != NULL);
        }
        else {
            entry = NULL;
        }
 
        *isolation_error = UNLIKELY(!rb_ractor_main_p()) && (!entry || !entry->ractor_local);
 
        if (!entry && create_entry && !*isolation_error) {
            struct rb_global_variable *var = ALLOC(struct rb_global_variable);
            entry = ALLOC(struct rb_global_entry);
            entry->id = id;
            entry->var = var;
            entry->ractor_local = false;
            var->id = id;
            var->counter = 1;
            var->data = 0;
            var->getter = rb_gvar_undef_getter;
            var->setter = rb_gvar_undef_setter;
            var->marker = rb_gvar_undef_marker;
            var->compactor = rb_gvar_undef_compactor;
 
            var->block_trace = 0;
            var->trace = 0;
            var->box_ready = false;
            var->box_dynamic = false;
            rb_id_table_insert(rb_global_tbl, id, (VALUE)entry);
        }
    }
 
    return entry;
}
 
static struct rb_global_entry*
rb_find_global_entry(ID id)
{
    bool isolation_error;
    struct rb_global_entry *entry = global_entry_lookup(id, false, &isolation_error);
 
    if (isolation_error) global_entry_isolation_error(id);
 
    return entry;
}
 
void
rb_gvar_ractor_local(const char *name)
{
    struct rb_global_entry *entry = rb_find_global_entry(rb_intern(name));
    entry->ractor_local = true;
}
 
void
rb_gvar_box_ready(const char *name)
{
    struct rb_global_entry *entry = rb_find_global_entry(rb_intern(name));
    entry->var->box_ready = true;
}
 
void
rb_gvar_box_dynamic(const char *name)
{
    struct rb_global_entry *entry = rb_find_global_entry(rb_intern(name));
    entry->var->box_dynamic = true;
}
 
static struct rb_global_entry*
rb_global_entry(ID id)
{
    bool isolation_error;
    struct rb_global_entry *entry = global_entry_lookup(id, true, &isolation_error);
 
    if (isolation_error) global_entry_isolation_error(id);
 
    return entry;
}
 
VALUE
rb_gvar_undef_getter(ID id, VALUE *_)
{
    rb_warning("global variable '%"PRIsVALUE"' not initialized", QUOTE_ID(id));
 
    return Qnil;
}
 
static void
rb_gvar_val_compactor(void *_var)
{
    struct rb_global_variable *var = (struct rb_global_variable *)_var;
 
    if (var->data) {
        rb_gc_update_moved_ptr(&var->data);
    }
}
 
void
rb_gvar_undef_setter(VALUE val, ID id, VALUE *_)
{
    struct rb_global_variable *var = rb_global_entry(id)->var;
    var->getter = rb_gvar_val_getter;
    var->setter = rb_gvar_val_setter;
    var->marker = rb_gvar_val_marker;
    var->compactor = rb_gvar_val_compactor;
 
    var->data = (void*)val;
}
 
void
rb_gvar_undef_marker(VALUE *var)
{
}
 
VALUE
rb_gvar_val_getter(ID id, VALUE *data)
{
    return (VALUE)data;
}
 
void
rb_gvar_val_setter(VALUE val, ID id, VALUE *_)
{
    struct rb_global_variable *var = rb_global_entry(id)->var;
    var->data = (void*)val;
}
 
void
rb_gvar_val_marker(VALUE *var)
{
    VALUE data = (VALUE)var;
    if (data) rb_gc_mark_movable(data);
}
 
VALUE
rb_gvar_var_getter(ID id, VALUE *var)
{
    if (!var) return Qnil;
    return *var;
}
 
void
rb_gvar_var_setter(VALUE val, ID id, VALUE *data)
{
    *data = val;
}
 
void
rb_gvar_var_marker(VALUE *var)
{
    if (var) rb_gc_mark_maybe(*var);
}
 
void
rb_gvar_readonly_setter(VALUE v, ID id, VALUE *_)
{
    rb_name_error(id, "%"PRIsVALUE" is a read-only variable", QUOTE_ID(id));
}
 
static enum rb_id_table_iterator_result
mark_global_entry(VALUE v, void *ignored)
{
    struct rb_global_entry *entry = (struct rb_global_entry *)v;
    struct trace_var *trace;
    struct rb_global_variable *var = entry->var;
 
    (*var->marker)(var->data);
    trace = var->trace;
    while (trace) {
        if (trace->data) rb_gc_mark_maybe(trace->data);
        trace = trace->next;
    }
    return ID_TABLE_CONTINUE;
}
 
#define gc_mark_table(task) \
    if (rb_global_tbl) { rb_id_table_foreach_values(rb_global_tbl, task##_global_entry, 0); }
 
void
rb_gc_mark_global_tbl(void)
{
    gc_mark_table(mark);
}
 
static enum rb_id_table_iterator_result
update_global_entry(VALUE v, void *ignored)
{
    struct rb_global_entry *entry = (struct rb_global_entry *)v;
    struct rb_global_variable *var = entry->var;
 
    (*var->compactor)(var);
    return ID_TABLE_CONTINUE;
}
 
void
rb_gc_update_global_tbl(void)
{
    gc_mark_table(update);
}
 
static ID
global_id(const char *name)
{
    ID id;
 
    if (name[0] == '$') id = rb_intern(name);
    else {
        size_t len = strlen(name);
        VALUE vbuf = 0;
        char *buf = ALLOCV_N(char, vbuf, len+1);
        buf[0] = '$';
        memcpy(buf+1, name, len);
        id = rb_intern2(buf, len+1);
        ALLOCV_END(vbuf);
    }
    return id;
}
 
static ID
find_global_id(const char *name)
{
    ID id;
    size_t len = strlen(name);
 
    if (name[0] == '$') {
        id = rb_check_id_cstr(name, len, NULL);
    }
    else {
        VALUE vbuf = 0;
        char *buf = ALLOCV_N(char, vbuf, len+1);
        buf[0] = '$';
        memcpy(buf+1, name, len);
        id = rb_check_id_cstr(buf, len+1, NULL);
        ALLOCV_END(vbuf);
    }
 
    return id;
}
 
void
rb_define_hooked_variable(
    const char *name,
    VALUE *var,
    rb_gvar_getter_t *getter,
    rb_gvar_setter_t *setter)
{
    volatile VALUE tmp = var ? *var : Qnil;
    ID id = global_id(name);
    struct rb_global_variable *gvar = rb_global_entry(id)->var;
 
    gvar->data = (void*)var;
    gvar->getter = getter ? (rb_gvar_getter_t *)getter : rb_gvar_var_getter;
    gvar->setter = setter ? (rb_gvar_setter_t *)setter : rb_gvar_var_setter;
    gvar->marker = rb_gvar_var_marker;
 
    RB_GC_GUARD(tmp);
}
 
void
rb_define_variable(const char *name, VALUE *var)
{
    rb_define_hooked_variable(name, var, 0, 0);
}
 
void
rb_define_readonly_variable(const char *name, const VALUE *var)
{
    rb_define_hooked_variable(name, (VALUE *)var, 0, rb_gvar_readonly_setter);
}
 
void
rb_define_virtual_variable(
    const char *name,
    rb_gvar_getter_t *getter,
    rb_gvar_setter_t *setter)
{
    if (!getter) getter = rb_gvar_val_getter;
    if (!setter) setter = rb_gvar_readonly_setter;
    rb_define_hooked_variable(name, 0, getter, setter);
}
 
static void
rb_trace_eval(VALUE cmd, VALUE val)
{
    rb_eval_cmd_call_kw(cmd, 1, &val, RB_NO_KEYWORDS);
}
 
VALUE
rb_f_trace_var(int argc, const VALUE *argv)
{
    VALUE var, cmd;
    struct rb_global_entry *entry;
    struct trace_var *trace;
 
    if (rb_scan_args(argc, argv, "11", &var, &cmd) == 1) {
        cmd = rb_block_proc();
    }
    if (NIL_P(cmd)) {
        return rb_f_untrace_var(argc, argv);
    }
    entry = rb_global_entry(rb_to_id(var));
    trace = ALLOC(struct trace_var);
    trace->next = entry->var->trace;
    trace->func = rb_trace_eval;
    trace->data = cmd;
    trace->removed = 0;
    entry->var->trace = trace;
 
    return Qnil;
}
 
static void
remove_trace(struct rb_global_variable *var)
{
    struct trace_var *trace = var->trace;
    struct trace_var t;
    struct trace_var *next;
 
    t.next = trace;
    trace = &t;
    while (trace->next) {
        next = trace->next;
        if (next->removed) {
            trace->next = next->next;
            SIZED_FREE(next);
        }
        else {
            trace = next;
        }
    }
    var->trace = t.next;
}
 
VALUE
rb_f_untrace_var(int argc, const VALUE *argv)
{
    VALUE var, cmd;
    ID id;
    struct rb_global_entry *entry;
    struct trace_var *trace;
 
    rb_scan_args(argc, argv, "11", &var, &cmd);
    id = rb_check_id(&var);
    if (!id) {
        rb_name_error_str(var, "undefined global variable %"PRIsVALUE"", QUOTE(var));
    }
    if ((entry = rb_find_global_entry(id)) == NULL) {
        rb_name_error(id, "undefined global variable %"PRIsVALUE"", QUOTE_ID(id));
    }
 
    trace = entry->var->trace;
    if (NIL_P(cmd)) {
        VALUE ary = rb_ary_new();
 
        while (trace) {
            struct trace_var *next = trace->next;
            rb_ary_push(ary, (VALUE)trace->data);
            trace->removed = 1;
            trace = next;
        }
 
        if (!entry->var->block_trace) remove_trace(entry->var);
        return ary;
    }
    else {
        while (trace) {
            if (trace->data == cmd) {
                trace->removed = 1;
                if (!entry->var->block_trace) remove_trace(entry->var);
                return rb_ary_new3(1, cmd);
            }
            trace = trace->next;
        }
    }
    return Qnil;
}
 
struct trace_data {
    struct trace_var *trace;
    VALUE val;
};
 
static VALUE
trace_ev(VALUE v)
{
    struct trace_data *data = (void *)v;
    struct trace_var *trace = data->trace;
 
    while (trace) {
        (*trace->func)(trace->data, data->val);
        trace = trace->next;
    }
 
    return Qnil;
}
 
static VALUE
trace_en(VALUE v)
{
    struct rb_global_variable *var = (void *)v;
    var->block_trace = 0;
    remove_trace(var);
    return Qnil;                /* not reached */
}
 
static void
gvar_trace(struct rb_global_variable *var, VALUE val)
{
    struct trace_data trace;
 
    if (var->trace && !var->block_trace) {
        var->block_trace = 1;
        trace.trace = var->trace;
        trace.val = val;
        rb_ensure(trace_ev, (VALUE)&trace, trace_en, (VALUE)var);
    }
}
 
static VALUE
rb_gvar_set_entry(struct rb_global_entry *entry, VALUE val)
{
    struct rb_global_variable *var = entry->var;
 
    (*var->setter)(val, entry->id, var->data);
    gvar_trace(var, val);
    return val;
}
 
static inline bool
gvar_use_box_tbl(const rb_box_t *box, const struct rb_global_entry *entry)
{
    return BOX_USER_P(box) &&
        !entry->var->box_dynamic &&
        (!entry->var->box_ready || entry->var->setter != rb_gvar_readonly_setter);
}
 
VALUE
rb_gvar_set(ID id, VALUE val)
{
    VALUE retval;
    struct rb_global_entry *entry = NULL;
    const rb_box_t *box = rb_current_box();
    bool use_box_tbl = false;
    bool isolation_error = false;
 
    RB_VM_LOCKING() {
        entry = global_entry_lookup(id, true, &isolation_error);
 
        if (!isolation_error && gvar_use_box_tbl(box, entry)) {
            use_box_tbl = true;
            rb_hash_aset(box->gvar_tbl, rb_id2sym(entry->var->id), val);
            retval = val;
        }
    }
 
    if (isolation_error) global_entry_isolation_error(id);
 
    if (use_box_tbl) {
        gvar_trace(entry->var, val);
    }
    else {
        retval = rb_gvar_set_entry(entry, val);
    }
    return retval;
}
 
VALUE
rb_gv_set(const char *name, VALUE val)
{
    return rb_gvar_set(global_id(name), val);
}
 
VALUE
rb_gvar_get(ID id)
{
    VALUE retval, gvars, key;
    const rb_box_t *box = rb_current_box();
    bool use_box_tbl = false;
    bool isolation_error = false;
    struct rb_global_entry *entry = NULL;
    struct rb_global_variable *var = NULL;
 
    RB_VM_LOCKING() {
        // TODO: use lock-free rb_id_table when it's available for use (doesn't yet exist)
        entry = global_entry_lookup(id, true, &isolation_error);
 
        if (!isolation_error) {
            var = entry->var;
 
            if (gvar_use_box_tbl(box, entry)) {
                use_box_tbl = true;
                gvars = box->gvar_tbl;
                key = rb_id2sym(var->id);
                if (RTEST(rb_hash_has_key(gvars, key))) { // this gvar is already cached
                    retval = rb_hash_aref(gvars, key);
                }
                else {
                    // An undefined gvar has no value to snapshot, and caching its nil
                    // would make rb_gvar_defined() report it as defined in this box.
                    bool cache = var->getter != rb_gvar_undef_getter;
                    RB_VM_UNLOCK();
                    {
                        retval = (*var->getter)(entry->id, var->data);
                        if (rb_obj_respond_to(retval, rb_intern("clone"), 1)) {
                            retval = rb_funcall(retval, rb_intern("clone"), 0);
                        }
                    }
                    RB_VM_LOCK();
                    if (cache) rb_hash_aset(gvars, key, retval);
                }
            }
        }
    }
 
    if (isolation_error) global_entry_isolation_error(id);
 
    if (!use_box_tbl) {
        retval = (*var->getter)(entry->id, var->data);
    }
    return retval;
}
 
VALUE
rb_gv_get(const char *name)
{
    ID id = find_global_id(name);
 
    if (!id) {
        rb_warning("global variable '%s' not initialized", name);
        return Qnil;
    }
 
    return rb_gvar_get(id);
}
 
VALUE
rb_gvar_defined(ID id)
{
    const rb_box_t *box = rb_current_box();
    bool defined;
 
    RB_VM_LOCKING() {
        const struct rb_global_entry *entry = rb_global_entry(id);
 
        defined = entry->var->getter != rb_gvar_undef_getter ||
            (gvar_use_box_tbl(box, entry) &&
             RTEST(rb_hash_has_key(box->gvar_tbl, rb_id2sym(entry->var->id))));
    }
    return RBOOL(defined);
}
 
rb_gvar_getter_t *
rb_gvar_getter_function_of(ID id)
{
    const struct rb_global_entry *entry = rb_global_entry(id);
    return entry->var->getter;
}
 
rb_gvar_setter_t *
rb_gvar_setter_function_of(ID id)
{
    const struct rb_global_entry *entry = rb_global_entry(id);
    return entry->var->setter;
}
 
static enum rb_id_table_iterator_result
gvar_i(ID key, VALUE val, void *a)
{
    VALUE ary = (VALUE)a;
    rb_ary_push(ary, ID2SYM(key));
    return ID_TABLE_CONTINUE;
}
 
VALUE
rb_f_global_variables(void)
{
    VALUE ary = rb_ary_new();
    VALUE sym, backref = rb_backref_get();
 
    if (!rb_ractor_main_p()) {
        rb_raise(rb_eRactorIsolationError, "can not access global variables from non-main Ractors");
    }
    /* gvar access (get/set) in boxes creates gvar entries globally */
 
    rb_id_table_foreach(rb_global_tbl, gvar_i, (void *)ary);
    if (!NIL_P(backref)) {
        char buf[2];
        int i, nmatch = rb_match_count(backref);
        buf[0] = '$';
        for (i = 1; i <= nmatch; ++i) {
            if (!RTEST(rb_reg_nth_defined(i, backref))) continue;
            if (i < 10) {
                /* probably reused, make static ID */
                buf[1] = (char)(i + '0');
                sym = ID2SYM(rb_intern2(buf, 2));
            }
            else {
                /* dynamic symbol */
                sym = rb_str_intern(rb_sprintf("$%d", i));
            }
            rb_ary_push(ary, sym);
        }
    }
    return ary;
}
 
void
rb_alias_variable(ID name1, ID name2)
{
    struct rb_global_entry *entry1 = NULL, *entry2;
    VALUE data1;
    struct rb_id_table *gtbl = rb_global_tbl;
    bool tracer_error = false;
 
    if (!rb_ractor_main_p()) {
        rb_raise(rb_eRactorIsolationError, "can not access global variables from non-main Ractors");
    }
 
    RB_VM_LOCKING() {
        bool isolation_error;
        entry2 = global_entry_lookup(name2, true, &isolation_error);
        VM_ASSERT(!isolation_error); /* main Ractor, checked above */
 
        if (!rb_id_table_lookup(gtbl, name1, &data1)) {
            entry1 = ZALLOC(struct rb_global_entry);
            entry1->id = name1;
            rb_id_table_insert(gtbl, name1, (VALUE)entry1);
        }
        else if ((entry1 = (struct rb_global_entry *)data1)->var != entry2->var) {
            struct rb_global_variable *var = entry1->var;
            if (var->block_trace) {
                tracer_error = true;
            }
            else {
                var->counter--;
                if (var->counter == 0) {
                    free_global_variable(var);
                }
            }
        }
        if (!tracer_error && entry1->var != entry2->var) {
            entry2->var->counter++;
            entry1->var = entry2->var;
        }
    }
 
    if (tracer_error) rb_raise(rb_eRuntimeError, "can't alias in tracer");
}
 
static void
class_ivar_set_ractor_check(VALUE klass, ID id)
{
    if (rb_is_instance_id(id) && // check only normal ivars
        UNLIKELY(!rb_class_owned_p(klass))) {
        rb_raise(
            rb_eRactorIsolationError,
            "can not set instance variables of classes/modules "
            "created by another Ractor (%"PRIsVALUE" from %"PRIsVALUE")",
            rb_id2str(id),
            rb_class_path(klass)
        );
    }
}
 
// klass is the class the variable is stored in, not the receiver: which one that
// is can migrate (cvar_overtaken), and it is the one with a single writer.
static void
cvar_set_ractor_check(VALUE klass, ID id)
{
    if (UNLIKELY(!rb_class_owned_p(klass))) {
        rb_raise(rb_eRactorIsolationError,
                 "can not set class variable %"PRIsVALUE" of %"PRIsVALUE", which was created by another Ractor",
                 rb_id2str(id), klass);
    }
}
 
static void
cvar_read_ractor_check(VALUE klass, ID id, VALUE val)
{
    if (UNLIKELY(!rb_class_owned_p(klass)) && !rb_class_field_shareable_p(klass, val)) {
        rb_raise(rb_eRactorIsolationError,
                 "can not read non-shareable class variable %"PRIsVALUE" of %"PRIsVALUE", which was created by another Ractor",
                 rb_id2str(id), klass);
    }
}
 
static inline void
ivar_ractor_assert(VALUE obj, ID id)
{
    RUBY_ASSERT(!rb_is_instance_id(id) /* internal ID */ ||
                SPECIAL_CONST_P(obj) ||
                !rb_ractor_shareable_p(obj) ||
                RB_OBJ_FROZEN_RAW(obj) ||
                RB_TYPE_P(obj, T_CLASS) || RB_TYPE_P(obj, T_MODULE) ||
                RB_TYPE_P(obj, T_ICLASS) || RB_TYPE_P(obj, T_IMEMO) ||
                rb_shape_frozen_p(RBASIC_SHAPE_ID(obj)),
                "shareable object must not have writable instance variables");
}
 
struct st_table *
rb_generic_fields_tbl_get(void)
{
    return generic_fields_tbl_;
}
 
/* generic_fields is one global table.  Leaf lock discipline: under gf_lock, take no
 * other lock, do not allocate, and create no safepoint.  In single-Ractor mode the
 * GVL already serializes everything, so no lock is taken. */
static inline void
gf_lock(void)
{
    if (rb_multi_ractor_p()) {
        rb_native_mutex_lock(&GET_VM()->ractor.generic_fields_lock);
    }
}
 
static inline void
gf_unlock(void)
{
    if (rb_multi_ractor_p()) {
        rb_native_mutex_unlock(&GET_VM()->ractor.generic_fields_lock);
    }
}
 
void
rb_mark_generic_ivar(VALUE obj)
{
    /* Under a multi-objspace global GC (stop-the-world) there is no per-object
     * lookup: after marking, rb_gc_vm_generic_fields_mark_foreach marks the values of
     * the live keys.  A single-objspace impl (mmtk) has no such pass, so mark here. */
    if (rb_gc_during_global_gc_p() && rb_gc_multi_objspace_p()) {
        return;
    }
 
    /* Per-object marking for a local GC or for compaction (single objspace).  gf_lock
     * excludes writers in other Ractors. */
    VALUE data = 0;
    gf_lock();
    st_lookup(generic_fields_tbl_, (st_data_t)obj, (st_data_t *)&data);
    gf_unlock();
    if (data) {
        rb_gc_mark_movable(data);
    }
}
 
/* Look up obj's generic fields in the single global table.  A snapshot host being
 * materialized (which lives in the sender's objspace) is in the same table, so the
 * receiving side can look it up directly. */
VALUE
rb_obj_fields_generic_uncached(VALUE obj)
{
    VALUE fields_obj = 0;
    int found = 0;
 
    gf_lock();
    found = st_lookup(generic_fields_tbl_, (st_data_t)obj, (st_data_t *)&fields_obj);
    gf_unlock();
 
    if (!found) {
        rb_bug("Object is missing entry in generic_fields_tbl");
    }
    return fields_obj;
}
 
static bool
obj_use_generic_fields_tbl_p(VALUE obj)
{
    switch (BUILTIN_TYPE(obj)) {
      case T_OBJECT:
      case T_CLASS:
      case T_MODULE:
      case T_STRUCT:
      case T_DATA:
        return false;
      default:
        return true;
    }
}
 
VALUE
rb_obj_fields(VALUE obj, ID field_name)
{
    ivar_ractor_assert(obj, field_name);
 
    switch (BUILTIN_TYPE(obj)) {
      case T_IMEMO:
        RUBY_ASSERT(IMEMO_TYPE_P(obj, imemo_fields));
        return obj;
 
      case T_OBJECT:
        return ROBJECT_FIELDS_OBJ(obj);
 
      case T_CLASS:
      case T_MODULE:
        return RCLASS_WRITABLE_FIELDS_OBJ(obj);
 
      case T_DATA:
        return rbimpl_atomic_value_load(&RTYPEDDATA(obj)->fields_obj, RBIMPL_ATOMIC_ACQUIRE);
 
      case T_STRUCT:
        return RSTRUCT_FIELDS_OBJ(obj);
 
      default:
        {
            VALUE fields_obj = 0;
 
            if (rb_obj_shape_has_fields(obj)) {
                rb_execution_context_t *ec = GET_EC();
                if (ec->gen_fields_cache.obj == obj && !UNDEF_P(ec->gen_fields_cache.fields_obj) && rb_imemo_fields_owner(ec->gen_fields_cache.fields_obj) == obj) {
                    fields_obj = ec->gen_fields_cache.fields_obj;
                    RUBY_ASSERT(fields_obj == rb_obj_fields_generic_uncached(obj));
                }
                else {
                    fields_obj = rb_obj_fields_generic_uncached(obj);
                    ec->gen_fields_cache.fields_obj = fields_obj;
                    ec->gen_fields_cache.obj = obj;
                }
            }
 
            return fields_obj;
        }
    }
}
 
void
rb_free_generic_ivar(VALUE obj)
{
    if (rb_obj_gen_fields_p(obj)) {
        st_data_t key = (st_data_t)obj, value;
        switch (BUILTIN_TYPE(obj)) {
          case T_DATA:
            RB_OBJ_WRITE(obj, &RTYPEDDATA(obj)->fields_obj, 0);
            break;
          case T_STRUCT:
            RSTRUCT_SET_FIELDS_OBJ(obj, 0);
            break;
 
          default:
            {
                // Other EC may have stale caches, so fields_obj should be
                // invalidated and the GC will replace with Qundef
                rb_execution_context_t *ec = GET_EC();
                if (ec->gen_fields_cache.obj == obj) {
                    ec->gen_fields_cache.obj = Qundef;
                    ec->gen_fields_cache.fields_obj = Qundef;
                }
                /* A write from the mutator or from a local GC sweep (the host's
                 * obj_free), taking the table's mutex; never from a global GC sweep
                 * (the during_global_gc guard below). */
                if (rb_gc_during_global_gc_p() || ruby_vm_during_cleanup) {
                    /* Leave dead keys to the weak pass's drain (same reasoning as the
                     * skip in rb_mark_generic_ivar); VM destruct's free-at-exit walk
                     * discards the whole table, needing no per-entry removal either. */
                    break;
                }
                int deleted = 0;
                gf_lock();
                deleted = st_delete(generic_fields_tbl_, &key, &value);
                gf_unlock();
                if (!deleted) {
                    rb_bug("Object is missing entry in generic_fields_tbl");
                }
            }
        }
        RBASIC_SET_SHAPE_ID(obj, ROOT_SHAPE_ID);
    }
}
 
static void
rb_obj_set_fields(VALUE obj, VALUE fields_obj, ID field_name, VALUE original_fields_obj)
{
    ivar_ractor_assert(obj, field_name);
 
    if (!fields_obj) {
        RUBY_ASSERT(original_fields_obj);
        rb_free_generic_ivar(obj);
        rb_imemo_fields_clear(original_fields_obj);
        return;
    }
 
    RUBY_ASSERT(IMEMO_TYPE_P(fields_obj, imemo_fields));
    RUBY_ASSERT(!original_fields_obj || IMEMO_TYPE_P(original_fields_obj, imemo_fields) || RB_TYPE_P(original_fields_obj, T_OBJECT));
 
    int type = BUILTIN_TYPE(obj);
    if (fields_obj != original_fields_obj) {
        switch (type) {
          case T_OBJECT:
            RUBY_ASSERT(obj != fields_obj);
            ROBJECT_SET_EXTENDED(obj, fields_obj);
            break;
          case T_DATA:
            RB_OBJ_ATOMIC_WRITE(obj, &RTYPEDDATA(obj)->fields_obj, fields_obj);
            break;
          case T_STRUCT:
            RSTRUCT_SET_FIELDS_OBJ(obj, fields_obj);
            break;
 
          default:
            {
                /* st_insert may malloc: disable this Ractor's GC first, or our own
                 * local GC's marking takes gf_lock again and self-deadlocks.  Growing
                 * can still raise NoMemoryError, and leaking gf_lock hangs every later
                 * generic-fields access: unwind through a tag. */
                bool gc_disabled = RTEST(rb_gc_local_disable_no_rest());
                rb_execution_context_t *insert_ec = GET_EC();
                enum ruby_tag_type state;
                gf_lock();
                EC_PUSH_TAG(insert_ec);
                if ((state = EC_EXEC_TAG()) == TAG_NONE) {
                    st_insert(generic_fields_tbl_, (st_data_t)obj, (st_data_t)fields_obj);
                }
                EC_POP_TAG();
                gf_unlock();
                if (!gc_disabled) rb_gc_local_enable();
                if (state != TAG_NONE) EC_JUMP_TAG(insert_ec, state);
                RB_OBJ_WRITTEN(obj, original_fields_obj, fields_obj);
 
                rb_execution_context_t *ec = GET_EC();
                if (ec->gen_fields_cache.fields_obj != fields_obj) {
                    ec->gen_fields_cache.obj = obj;
                    ec->gen_fields_cache.fields_obj = fields_obj;
                }
            }
        }
 
        if (original_fields_obj && original_fields_obj != obj) {
            // Clear root shape to avoid triggering cleanup such as free_object_id.
            rb_imemo_fields_clear(original_fields_obj);
        }
    }
 
    if (type == T_OBJECT) {
        RBASIC_SET_SHAPE_ID_WITH_LAYOUT(obj, RBASIC_SHAPE_ID(fields_obj), SHAPE_ID_LAYOUT_EXTENDED);
    }
    else {
        RBASIC_SET_SHAPE_ID(obj, RBASIC_SHAPE_ID(fields_obj));
    }
}
 
void
rb_obj_replace_fields(VALUE obj, VALUE fields_obj)
{
    if (obj_use_generic_fields_tbl_p(obj)) {
        // We'll first lookup the generic fields table and then insert
        // into it, so lock once for both operations.
        RB_VM_LOCKING() {
            VALUE original_fields_obj = rb_obj_fields_no_ractor_check(obj);
            rb_obj_set_fields(obj, fields_obj, 0, original_fields_obj);
        }
    }
    else {
        VALUE original_fields_obj = rb_obj_fields_no_ractor_check(obj);
        rb_obj_set_fields(obj, fields_obj, 0, original_fields_obj);
    }
}
 
VALUE
rb_imemo_fields_field_get(VALUE fields_obj, shape_id_t target_shape_id)
{
    RUBY_ASSERT(RSHAPE_TYPE_P(target_shape_id, SHAPE_IVAR) || RSHAPE_TYPE_P(target_shape_id, SHAPE_OBJ_ID));
 
    if (UNLIKELY(rb_shape_complex_p(target_shape_id))) {
        st_table *fields_hash = rb_imemo_fields_complex_tbl(fields_obj);
        VALUE value = Qundef;
        st_lookup(fields_hash, RSHAPE_EDGE_NAME(target_shape_id), &value);
        RUBY_ASSERT(!UNDEF_P(value));
        return value;
    }
 
    attr_index_t index = RSHAPE_INDEX(target_shape_id);
    return rb_imemo_fields_ptr(fields_obj)[index];
}
 
VALUE
rb_obj_field_get(VALUE obj, shape_id_t target_shape_id)
{
    RUBY_ASSERT(!SPECIAL_CONST_P(obj));
 
    return rb_imemo_fields_field_get(rb_obj_fields(obj, RSHAPE_EDGE_NAME(target_shape_id)), target_shape_id);
}
 
VALUE
rb_ivar_lookup(VALUE obj, ID id, VALUE undef)
{
    if (SPECIAL_CONST_P(obj)) return undef;
 
    int type = BUILTIN_TYPE(obj);
    bool is_class = type == T_CLASS || type == T_MODULE;
    VALUE fields_obj = rb_obj_fields(obj, is_class ? 0 : id);
 
    if (!fields_obj) {
        return undef;
    }
 
    shape_id_t shape_id = RBASIC_SHAPE_ID(fields_obj);
 
    VALUE val = undef;
    if (UNLIKELY(rb_shape_complex_p(shape_id))) {
        st_table *iv_table = rb_imemo_fields_complex_tbl(fields_obj);
        if (!rb_st_lookup(iv_table, (st_data_t)id, (st_data_t *)&val)) {
            return undef;
        }
    }
    else {
        attr_index_t index = 0;
        if (!rb_shape_get_iv_index(shape_id, id, &index)) {
            return undef;
        }
        val = rb_imemo_fields_ptr(fields_obj)[index];
    }
 
    if (is_class && val != undef && rb_is_instance_id(id)) {
        if (UNLIKELY(!rb_class_owned_p(obj)) && !rb_class_field_shareable_p(obj, val)) {
            rb_raise(
                rb_eRactorIsolationError,
                "can not get unshareable values from instance variables of classes/modules "
                "created by another Ractor (%"PRIsVALUE" from %"PRIsVALUE")",
                rb_id2str(id),
                rb_class_path(obj)
            );
        }
    }
 
    return val;
}
 
VALUE
rb_ivar_get(VALUE obj, ID id)
{
    VALUE iv = rb_ivar_lookup(obj, id, Qnil);
    RB_DEBUG_COUNTER_INC(ivar_get_base);
    return iv;
}
 
VALUE
rb_ivar_get_at(VALUE obj, attr_index_t index, ID id)
{
    RUBY_ASSERT(rb_is_instance_id(id));
    // Used by JITs, but never for T_OBJECT.
 
    switch (BUILTIN_TYPE(obj)) {
      case T_OBJECT:
        UNREACHABLE_RETURN(Qundef);
      case T_CLASS:
      case T_MODULE:
        {
            VALUE fields_obj = RCLASS_WRITABLE_FIELDS_OBJ(obj);
            VALUE val = rb_imemo_fields_ptr(fields_obj)[index];
 
            if (UNLIKELY(!rb_class_owned_p(obj)) && !rb_class_field_shareable_p(obj, val)) {
                rb_raise(
                    rb_eRactorIsolationError,
                    "can not get unshareable values from instance variables of classes/modules "
                    "created by another Ractor (%"PRIsVALUE" from %"PRIsVALUE")",
                    rb_id2str(id),
                    rb_class_path(obj)
                );
            }
 
            return val;
        }
      default:
        {
            VALUE fields_obj = rb_obj_fields(obj, id);
            return rb_imemo_fields_ptr(fields_obj)[index];
        }
    }
}
 
VALUE
rb_ivar_get_at_no_ractor_check(VALUE obj, attr_index_t index)
{
    // Used by JITs, but never for T_OBJECT.
 
    VALUE fields_obj = rb_obj_fields_no_ractor_check(obj);
    return rb_imemo_fields_ptr(fields_obj)[index];
}
 
VALUE
rb_attr_get(VALUE obj, ID id)
{
    return rb_ivar_lookup(obj, id, Qnil);
}
 
static VALUE imemo_fields_evacutate_to_complex(VALUE owner, VALUE source_fields_obj, shape_id_t shape_id, int extra_capa);
 
static shape_id_t
rb_obj_convert_too_complex(VALUE obj, VALUE fields_obj, shape_id_t shape_id)
{
    RUBY_ASSERT(RB_TYPE_P(obj, T_OBJECT));
    RUBY_ASSERT(!rb_obj_shape_complex_p(obj));
 
    shape_id = rb_shape_transition_complex(shape_id);
    VALUE new_fields_obj = imemo_fields_evacutate_to_complex(obj, fields_obj, shape_id, 1);
    ROBJECT_SET_EXTENDED(obj, new_fields_obj);
    RBASIC_SET_SHAPE_ID_WITH_LAYOUT(obj, shape_id, SHAPE_ID_LAYOUT_EXTENDED);
    return shape_id;
}
 
static VALUE
rb_ivar_delete(VALUE obj, ID id, VALUE undef)
{
    rb_check_frozen(obj);
 
    VALUE val = undef;
    bool concurrent = false;
    int type = BUILTIN_TYPE(obj);
 
    if (type == T_CLASS || type == T_MODULE) {
        class_ivar_set_ractor_check(obj, id);
 
        if (rb_multi_ractor_p()) {
            concurrent = true;
        }
    }
 
    VALUE fields_obj = rb_obj_fields(obj, id);
    if (!fields_obj) {
        return undef;
    }
 
    const VALUE original_fields_obj = fields_obj;
    if (concurrent) {
        fields_obj = rb_imemo_fields_clone(fields_obj);
    }
 
    shape_id_t old_shape_id = RBASIC_SHAPE_ID(fields_obj);
    shape_id_t removed_shape_id;
    shape_id_t next_shape_id = rb_obj_shape_transition_remove_ivar(fields_obj, id, &removed_shape_id);
 
    if (UNLIKELY(rb_shape_complex_p(next_shape_id))) {
        if (UNLIKELY(!rb_shape_complex_p(old_shape_id))) {
            fields_obj = imemo_fields_evacutate_to_complex(obj, fields_obj, next_shape_id, -1);
        }
        st_data_t key = id;
        if (!st_delete(rb_imemo_fields_complex_tbl(fields_obj), &key, (st_data_t *)&val)) {
            val = undef;
        }
    }
    else {
        if (next_shape_id == old_shape_id) {
            return undef;
        }
 
        RUBY_ASSERT(removed_shape_id != INVALID_SHAPE_ID);
        RUBY_ASSERT(RSHAPE_LEN(next_shape_id) == RSHAPE_LEN(old_shape_id) - 1);
 
        VALUE *fields = rb_imemo_fields_ptr(fields_obj);
        attr_index_t removed_index = RSHAPE_INDEX(removed_shape_id);
        val = fields[removed_index];
 
        attr_index_t new_fields_count = RSHAPE_LEN(next_shape_id);
        if (new_fields_count) {
            size_t trailing_fields = new_fields_count - removed_index;
 
            MEMMOVE(&fields[removed_index], &fields[removed_index + 1], VALUE, trailing_fields);
            RBASIC_SET_SHAPE_ID(fields_obj, next_shape_id);
 
            if (type == T_OBJECT && obj != fields_obj && new_fields_count == rb_shape_embedded_capacity(RBASIC_SHAPE_ID(obj))) {
                // Re-embed objects when instances become small enough
                // This is necessary because YJIT assumes that objects with the same shape
                // have the same embeddedness for efficiency (avoid extra checks)
                // Note: shapes have changed significantly since, we could not do this anymore.
                VALUE *embedded_fields = ROBJECT_EMBEDDED_FIELDS(obj);
                MEMCPY(embedded_fields, fields, VALUE, new_fields_count);
                for (attr_index_t i = 0; i < new_fields_count; i++) {
                    RB_OBJ_WRITTEN(obj, Qundef, embedded_fields[i]);
                }
                fields_obj = 0;
            }
        }
        else {
            fields_obj = 0;
            rb_free_generic_ivar(obj);
        }
    }
 
    if (fields_obj != original_fields_obj) {
        switch (type) {
          case T_OBJECT:
            if (fields_obj && fields_obj != obj) {
                ROBJECT_SET_EXTENDED(obj, fields_obj);
            }
            break;
          case T_CLASS:
          case T_MODULE:
            RCLASS_WRITABLE_SET_FIELDS_OBJ(obj, fields_obj);
            break;
          default:
            rb_obj_set_fields(obj, fields_obj, id, original_fields_obj);
            break;
        }
    }
 
    if (type == T_OBJECT) {
        if (!fields_obj || fields_obj == obj) {
            RBASIC_SET_SHAPE_ID_WITH_LAYOUT(obj, next_shape_id, SHAPE_ID_LAYOUT_ROBJECT);
        }
        else {
            RBASIC_SET_SHAPE_ID_WITH_LAYOUT(obj, next_shape_id, SHAPE_ID_LAYOUT_EXTENDED);
        }
    }
    else {
        RBASIC_SET_SHAPE_ID(obj, next_shape_id);
    }
 
    return val;
}
 
VALUE
rb_attr_delete(VALUE obj, ID id)
{
    return rb_ivar_delete(obj, id, Qnil);
}
 
static int
imemo_fields_complex_from_obj_i(ID key, VALUE val, st_data_t arg)
{
    VALUE fields = (VALUE)arg;
    st_table *table = rb_imemo_fields_complex_tbl(fields);
 
    RUBY_ASSERT(!st_lookup(table, (st_data_t)key, NULL));
    st_add_direct(table, (st_data_t)key, (st_data_t)val);
    RB_OBJ_WRITTEN(fields, Qundef, val);
 
    return ST_CONTINUE;
}
 
static int
imemo_fields_shref_i(ID key, VALUE val, st_data_t arg)
{
    VALUE fields_obj = (VALUE)arg;
    /* The fields_obj became shareable while this field value stayed unshareable (a
     * hidden [path, line] ivar, say, which make_shareable's traversal never reaches):
     * record a shref so the shareable -> unshareable edge is tracked. */
    if (!SPECIAL_CONST_P(val) && !RB_OBJ_SHAREABLE_P(val)) {
        rb_gc_writebarrier(fields_obj, val);
    }
    return ST_CONTINUE;
}
 
/* Record shrefs for the values that are still unshareable in a fields imemo that has
 * just been promoted to shareable. */
void
rb_imemo_fields_record_shrefs(VALUE fields_obj)
{
    rb_field_foreach(fields_obj, imemo_fields_shref_i, (st_data_t)fields_obj, false);
}
 
static VALUE
imemo_fields_complex_from_obj(VALUE owner, VALUE source, shape_id_t shape_id, bool ivar_only, int extra_capa)
{
    attr_index_t len = source ? RSHAPE_LEN(RBASIC_SHAPE_ID(source)) : 0;
    int capa = (len + extra_capa);
    RUBY_ASSERT(capa >= 0);
 
    VALUE fields_obj = rb_imemo_fields_new_complex(owner, shape_id, capa, RB_OBJ_SHAREABLE_P(owner));
 
    rb_field_foreach(source, imemo_fields_complex_from_obj_i, (st_data_t)fields_obj, ivar_only);
 
    return fields_obj;
}
 
static VALUE
imemo_fields_evacutate_to_complex(VALUE owner, VALUE source, shape_id_t shape_id, int extra_capa)
{
    return imemo_fields_complex_from_obj(owner, source, shape_id, false, extra_capa);
}
 
VALUE
rb_obj_complex_fields_build(VALUE obj)
{
    return imemo_fields_complex_from_obj(obj, obj, ROOT_COMPLEX_SHAPE_ID, true, 0);
}
 
static VALUE
imemo_fields_copy_append(VALUE owner, VALUE source_fields_obj, shape_id_t current_shape_id, shape_id_t target_shape_id, VALUE val)
{
    attr_index_t fields_count = RSHAPE_LEN(current_shape_id);
 
    VALUE fields_obj = rb_imemo_fields_new(owner, target_shape_id, RB_OBJ_SHAREABLE_P(owner));
 
    VALUE *fields = rb_imemo_fields_ptr(fields_obj);
 
    if (source_fields_obj) {
        MEMCPY(fields, rb_imemo_fields_ptr(source_fields_obj), VALUE, fields_count);
        for (attr_index_t i = 0; i < fields_count; i++) {
            RB_OBJ_WRITTEN(fields_obj, Qundef, fields[i]);
        }
    }
 
    RB_OBJ_WRITE(fields_obj, &fields[fields_count], val);
 
    return fields_obj;
}
 
static VALUE
imemo_fields_set(VALUE owner, VALUE fields_obj, shape_id_t target_shape_id, ID field_name, VALUE val, bool concurrent)
{
    const VALUE original_fields_obj = fields_obj;
    shape_id_t current_shape_id = fields_obj ? RBASIC_SHAPE_ID(fields_obj) : ROOT_SHAPE_ID;
 
    if (UNLIKELY(rb_shape_complex_p(target_shape_id))) {
        if (rb_shape_complex_p(current_shape_id)) {
            if (concurrent) {
                // In multi-ractor case, we must always work on a copy because
                // even if the field already exist, inserting in a st_table may
                // cause a rebuild.
                fields_obj = rb_imemo_fields_clone(fields_obj);
            }
        }
        else {
            fields_obj = imemo_fields_evacutate_to_complex(owner, original_fields_obj, target_shape_id, 1);
            current_shape_id = target_shape_id;
        }
 
        st_table *table = rb_imemo_fields_complex_tbl(fields_obj);
 
        RUBY_ASSERT(field_name);
        st_insert(table, (st_data_t)field_name, (st_data_t)val);
        RB_OBJ_WRITTEN(fields_obj, Qundef, val);
        RBASIC_SET_SHAPE_ID(fields_obj, target_shape_id);
    }
    else {
        attr_index_t index = RSHAPE_INDEX(target_shape_id);
        if (concurrent || index >= rb_shape_embedded_capacity(current_shape_id)) {
            return imemo_fields_copy_append(owner, original_fields_obj, current_shape_id, target_shape_id, val);
        }
 
        VALUE *table = rb_imemo_fields_ptr(fields_obj);
        RB_OBJ_WRITE(fields_obj, &table[index], val);
 
        if (index >= RSHAPE_LEN(current_shape_id)) {
            RBASIC_SET_SHAPE_ID(fields_obj, target_shape_id);
        }
    }
 
    return fields_obj;
}
 
static attr_index_t
generic_field_set(VALUE obj, shape_id_t target_shape_id, ID field_name, VALUE val)
{
    if (!field_name) {
        field_name = RSHAPE_EDGE_NAME(target_shape_id);
        RUBY_ASSERT(field_name);
    }
 
    const VALUE original_fields_obj = rb_obj_fields(obj, field_name);
    // Readers of a shareable object's fields take no lock, so never mutate a published fields_obj.
    bool concurrent = rb_multi_ractor_p() && RB_OBJ_SHAREABLE_P(obj);
    VALUE fields_obj = imemo_fields_set(obj, original_fields_obj, target_shape_id, field_name, val, concurrent);
 
    rb_obj_set_fields(obj, fields_obj, field_name, original_fields_obj);
    return rb_shape_complex_p(target_shape_id) ? ATTR_INDEX_NOT_SET : RSHAPE_INDEX(target_shape_id);
}
 
static shape_id_t
generic_shape_ivar(VALUE obj, ID id, bool *new_ivar_out)
{
    bool new_ivar = false;
    shape_id_t current_shape_id = RBASIC_SHAPE_ID(obj);
    shape_id_t target_shape_id = current_shape_id;
 
    if (!rb_shape_complex_p(current_shape_id)) {
        if (!rb_shape_find_ivar(current_shape_id, id, &target_shape_id)) {
            new_ivar = true;
            target_shape_id = rb_obj_shape_transition_add_ivar(obj, id);
        }
    }
 
    *new_ivar_out = new_ivar;
    return target_shape_id;
}
 
static attr_index_t
generic_ivar_set(VALUE obj, ID id, VALUE val)
{
    bool dontcare;
    shape_id_t target_shape_id = generic_shape_ivar(obj, id, &dontcare);
    return generic_field_set(obj, target_shape_id, id, val);
}
 
static attr_index_t
obj_field_set(VALUE obj, shape_id_t target_shape_id, ID field_name, VALUE val)
{
    // may be T_OBJECT or imemo_fields
    VALUE fields_obj = ROBJECT_FIELDS_OBJ(obj);
    shape_id_t current_shape_id = RBASIC_SHAPE_ID(obj);
 
    if (UNLIKELY(rb_shape_complex_p(target_shape_id))) {
        if (UNLIKELY(!rb_shape_complex_p(current_shape_id))) {
            current_shape_id = rb_obj_convert_too_complex(obj, fields_obj, current_shape_id);
            fields_obj = ROBJECT_FIELDS_OBJ(obj);
        }
 
        RUBY_ASSERT(rb_obj_shape_complex_p(obj));
        RUBY_ASSERT(rb_obj_shape_complex_p(fields_obj));
 
        if (!field_name) {
            field_name = RSHAPE_EDGE_NAME(target_shape_id);
            RUBY_ASSERT(field_name);
        }
 
        st_insert(rb_imemo_fields_complex_tbl(fields_obj), (st_data_t)field_name, (st_data_t)val);
        RB_OBJ_WRITTEN(fields_obj, Qundef, val);
 
        RBASIC_SET_SHAPE_ID(obj, target_shape_id);
        if (obj != fields_obj) {
            RBASIC_SET_SHAPE_ID(fields_obj, target_shape_id);
        }
 
        return ATTR_INDEX_NOT_SET;
    }
    else {
        attr_index_t index = RSHAPE_INDEX(target_shape_id);
 
        if (index < RSHAPE_LEN(current_shape_id)) {
            // Replace existing value;
            RB_OBJ_WRITE(fields_obj, &rb_imemo_fields_ptr(fields_obj)[index], val);
            return index;
        }
 
        RUBY_ASSERT(index == RSHAPE_LEN(current_shape_id));
 
        if (UNLIKELY(index >= RSHAPE_CAPACITY(current_shape_id))) {
            fields_obj = imemo_fields_copy_append(obj, fields_obj, current_shape_id, target_shape_id, val);
            ROBJECT_SET_EXTENDED(obj, fields_obj);
            RBASIC_SET_FULL_SHAPE_ID(obj, rb_shape_transition_layout(target_shape_id, SHAPE_ID_LAYOUT_EXTENDED));
        }
        else {
            RB_OBJ_WRITE(fields_obj, &rb_imemo_fields_ptr(fields_obj)[index], val);
            RBASIC_SET_SHAPE_ID(obj, target_shape_id);
        }
 
        if (obj != fields_obj) {
            RBASIC_SET_SHAPE_ID(fields_obj, target_shape_id);
        }
 
        return index;
    }
}
 
static attr_index_t
obj_ivar_set(VALUE obj, ID id, VALUE val)
{
    bool dontcare;
    shape_id_t target_shape_id = generic_shape_ivar(obj, id, &dontcare);
    return obj_field_set(obj, target_shape_id, id, val);
}
 
void
rb_check_ivar_modifiable(VALUE obj)
{
    if (UNLIKELY(!RB_FL_ABLE(obj) || rb_shape_frozen_p(RBASIC_SHAPE_ID(obj)))) {
        rb_check_frozen(obj);
 
        RUBY_ASSERT(RB_OBJ_SHAREABLE_P(obj), "unfrozen object with a frozen shape must be shareable");
 
        rb_raise(rb_eRactorIsolationError,
                 "can't modify instance variables of a shareable %"PRIsVALUE,
                 rb_obj_class(obj));
    }
    else if (UNLIKELY(CHILLED_STRING_P(obj))) {
        CHILLED_STRING_MUTATED(obj);
    }
 
    RUBY_ASSERT(!RB_OBJ_FROZEN_RAW(obj), "frozen object with an unfrozen shape");
}
 
/* Set the instance variable +val+ on object +obj+ at ivar name +id+.
 * This function only works with T_OBJECT objects, so make sure
 * +obj+ is of type T_OBJECT before using this function.
 */
VALUE
rb_vm_set_ivar_id(VALUE obj, ID id, VALUE val)
{
    rb_check_ivar_modifiable(obj);
    obj_ivar_set(obj, id, val);
    return val;
}
 
void
rb_obj_freeze_inline(VALUE x)
{
    if (RB_FL_ABLE(x)) {
        RB_FL_SET_RAW(x, RUBY_FL_FREEZE);
        if (TYPE(x) == T_STRING) {
            RB_FL_UNSET_RAW(x, FL_USER2); // STR_CHILLED
        }
 
        // rb_obj_freeze_inline(String)
        shape_id_t shape_id = rb_obj_shape_transition_frozen(x);
        switch (BUILTIN_TYPE(x)) {
          case T_CLASS:
          case T_MODULE:
            {
                VALUE fields_obj = RCLASS_WRITABLE_FIELDS_OBJ(x);
                if (fields_obj) {
                    rb_obj_freeze_inline(fields_obj);
                }
                else {
                    fields_obj = rb_imemo_fields_new(x, ROOT_SHAPE_ID, true);
                    rb_obj_freeze_inline(fields_obj);
                    RCLASS_WRITABLE_SET_FIELDS_OBJ(x, fields_obj);
                }
            }
            // FIXME: How to do multi-shape?
            RBASIC_SET_SHAPE_ID(x, shape_id);
            break;
          default:
            RBASIC_SET_SHAPE_ID(x, shape_id);
            break;
        }
 
        if (RBASIC_CLASS(x) && RCLASS_SINGLETON_P(RBASIC_CLASS(x))) {
            rb_freeze_singleton_class(x);
        }
    }
}
 
static attr_index_t class_ivar_set(VALUE obj, ID id, VALUE val, bool *new_ivar);
 
static attr_index_t
ivar_set(VALUE obj, ID id, VALUE val)
{
    RB_DEBUG_COUNTER_INC(ivar_set_base);
 
    switch (BUILTIN_TYPE(obj)) {
      case T_OBJECT:
        return obj_ivar_set(obj, id, val);
      case T_CLASS:
      case T_MODULE:
        {
            class_ivar_set_ractor_check(obj, id);
            bool dontcare;
            return class_ivar_set(obj, id, val, &dontcare);
        }
      default:
        return generic_ivar_set(obj, id, val);
    }
}
 
VALUE
rb_ivar_set(VALUE obj, ID id, VALUE val)
{
    rb_check_ivar_modifiable(obj);
    ivar_set(obj, id, val);
    return val;
}
 
attr_index_t
rb_ivar_set_index(VALUE obj, ID id, VALUE val)
{
    return ivar_set(obj, id, val);
}
 
void
rb_ivar_set_internal(VALUE obj, ID id, VALUE val)
{
    // should be internal instance variable name (no @ prefix)
    VM_ASSERT(!rb_is_instance_id(id));
 
    ivar_set(obj, id, val);
}
 
attr_index_t
rb_obj_field_set(VALUE obj, shape_id_t target_shape_id, ID field_name, VALUE val)
{
    switch (BUILTIN_TYPE(obj)) {
      case T_OBJECT:
        return obj_field_set(obj, target_shape_id, field_name, val);
      case T_CLASS:
      case T_MODULE:
        // The only field is object_id and T_CLASS handle it differently.
        rb_bug("Unreachable");
        break;
      default:
        return generic_field_set(obj, target_shape_id, field_name, val);
    }
}
 
static VALUE
ivar_defined0(VALUE obj, ID id)
{
    if (rb_obj_shape_complex_p(obj)) {
        // defined? doesn't require ractor checks
        VALUE fields_obj = rb_obj_fields_no_ractor_check(obj);
        st_table *table = rb_imemo_fields_complex_tbl(fields_obj);
 
        VALUE idx;
        if (!table || !rb_st_lookup(table, id, &idx)) {
            return Qfalse;
        }
 
        return Qtrue;
    }
    else {
        attr_index_t index;
        return RBOOL(rb_shape_get_iv_index(RBASIC_SHAPE_ID(obj), id, &index));
    }
}
 
VALUE
rb_ivar_defined(VALUE obj, ID id)
{
    if (SPECIAL_CONST_P(obj)) return Qfalse;
 
    VALUE defined = Qfalse;
    switch (BUILTIN_TYPE(obj)) {
      case T_CLASS:
      case T_MODULE:
        {
            VALUE fields_obj = RCLASS_WRITABLE_FIELDS_OBJ(obj);
            if (fields_obj) {
                defined = ivar_defined0(fields_obj, id);
            }
        }
        break;
      default:
        defined = ivar_defined0(obj, id);
        break;
    }
    return defined;
}
 
struct iv_itr_data {
    VALUE obj;
    struct gen_fields_tbl *fields_tbl;
    st_data_t arg;
    rb_ivar_foreach_callback_func *func;
    VALUE *fields;
    shape_id_t shape_id;
    bool ivar_only;
};
 
static int
iterate_over_shapes_callback(shape_id_t shape_id, void *data)
{
    struct iv_itr_data *itr_data = data;
 
    if (itr_data->ivar_only && !RSHAPE_TYPE_P(shape_id, SHAPE_IVAR)) {
        return ST_CONTINUE;
    }
 
    VALUE *fields;
    switch (BUILTIN_TYPE(itr_data->obj)) {
      case T_OBJECT:
        RUBY_ASSERT(!rb_obj_shape_complex_p(itr_data->obj));
        fields = ROBJECT_FIELDS(itr_data->obj);
        break;
      case T_IMEMO:
        RUBY_ASSERT(IMEMO_TYPE_P(itr_data->obj, imemo_fields));
        RUBY_ASSERT(!rb_obj_shape_complex_p(itr_data->obj));
 
        fields = rb_imemo_fields_ptr(itr_data->obj);
        break;
      default:
        rb_bug("Unreachable");
    }
 
    RUBY_ASSERT(itr_data->shape_id == RBASIC_SHAPE_ID(itr_data->obj));
 
    VALUE val = fields[RSHAPE_INDEX(shape_id)];
    int ret = itr_data->func(RSHAPE_EDGE_NAME(shape_id), val, itr_data->arg);
 
    RUBY_ASSERT(itr_data->shape_id == RBASIC_SHAPE_ID(itr_data->obj));
 
    return ret;
}
 
/*
 * Returns a flag to stop iterating depending on the result of +callback+.
 */
static void
iterate_over_shapes(shape_id_t shape_id, rb_ivar_foreach_callback_func *callback, struct iv_itr_data *itr_data)
{
    rb_shape_foreach_field(shape_id, iterate_over_shapes_callback, itr_data);
}
 
static int
each_hash_iv(st_data_t id, st_data_t val, st_data_t data)
{
    struct iv_itr_data * itr_data = (struct iv_itr_data *)data;
    rb_ivar_foreach_callback_func *callback = itr_data->func;
    if ((ID)id == rb_shape_tree.id_object_id) {
        return ST_CONTINUE;
    }
    return callback((ID)id, (VALUE)val, itr_data->arg);
}
 
static void
obj_fields_each(VALUE obj, rb_ivar_foreach_callback_func *func, st_data_t arg, bool ivar_only)
{
    struct iv_itr_data itr_data = {
        .obj = obj,
        .arg = arg,
        .func = func,
        .ivar_only = ivar_only,
    };
 
    VALUE fields_obj = ROBJECT_FIELDS_OBJ(obj);
    shape_id_t shape_id = RBASIC_SHAPE_ID(obj);
 
    if (rb_shape_complex_p(shape_id)) {
        st_foreach_safe(rb_imemo_fields_complex_tbl(fields_obj), each_hash_iv, (st_data_t)&itr_data);
    }
    else {
        itr_data.fields = rb_imemo_fields_ptr(fields_obj);
        itr_data.shape_id = shape_id;
        iterate_over_shapes(shape_id, func, &itr_data);
    }
}
 
static void
imemo_fields_each(VALUE fields_obj, rb_ivar_foreach_callback_func *func, st_data_t arg, bool ivar_only)
{
    IMEMO_TYPE_P(fields_obj, imemo_fields);
 
    struct iv_itr_data itr_data = {
        .obj = fields_obj,
        .arg = arg,
        .func = func,
        .ivar_only = ivar_only,
    };
 
    shape_id_t shape_id = RBASIC_SHAPE_ID(fields_obj);
    if (rb_shape_complex_p(shape_id)) {
        rb_st_foreach(rb_imemo_fields_complex_tbl(fields_obj), each_hash_iv, (st_data_t)&itr_data);
    }
    else {
        itr_data.fields = rb_imemo_fields_ptr(fields_obj);
        itr_data.shape_id = shape_id;
        iterate_over_shapes(shape_id, func, &itr_data);
    }
}
 
void
rb_copy_generic_ivar(VALUE dest, VALUE obj)
{
    VALUE new_fields_obj;
 
    rb_check_frozen(dest);
 
    if (!rb_obj_gen_fields_p(obj)) {
        return;
    }
 
    shape_id_t src_shape_id = rb_obj_shape_id(obj);
 
    VALUE fields_obj = rb_obj_fields_no_ractor_check(obj);
    if (fields_obj) {
        unsigned long src_num_ivs = rb_ivar_count(fields_obj);
        if (!src_num_ivs) {
            rb_free_generic_ivar(dest);
            return;
        }
 
        shape_id_t initial_shape_id = rb_obj_shape_id(dest);
        shape_id_t dest_shape_id = rb_shape_rebuild(initial_shape_id, src_shape_id);
 
        if (UNLIKELY(rb_shape_complex_p(dest_shape_id))) {
            rb_obj_replace_fields(dest, rb_obj_complex_fields_build(obj));
            return;
        }
 
        if (!RSHAPE_LEN(dest_shape_id)) {
            RBASIC_SET_SHAPE_ID(dest, dest_shape_id);
            return;
        }
 
        new_fields_obj = rb_imemo_fields_new(dest, dest_shape_id, RB_OBJ_SHAREABLE_P(dest));
        VALUE *src_buf = rb_imemo_fields_ptr(fields_obj);
        VALUE *dest_buf = rb_imemo_fields_ptr(new_fields_obj);
        rb_shape_copy_fields(new_fields_obj, dest_buf, dest_shape_id, src_buf, src_shape_id);
 
        rb_obj_replace_fields(dest, new_fields_obj);
    }
}
 
/* Reference updating for compaction: walk the generic_fields table under the lock,
 * from a local GC's update phase, because moving a host in our own objspace leaves the
 * table's keys and values stale.  This only updates; it never decides liveness. */
void
rb_generic_fields_shared_table_foreach(void (*cb)(struct st_table *tbl, void *arg), void *arg)
{
    rb_native_mutex_lock(&GET_VM()->ractor.generic_fields_lock);
    if (generic_fields_tbl_ != NULL) {
        cb(generic_fields_tbl_, arg);
    }
    rb_native_mutex_unlock(&GET_VM()->ractor.generic_fields_lock);
}
 
/* Call cb(tbl, arg) for the single global generic_fields table.  Used by the global
 * GC's weak pass and by compaction's reference update; both run under the barrier, so
 * the walk needs no lock. */
void
rb_generic_fields_tables_foreach(void (*cb)(struct st_table *tbl, void *arg), void *arg)
{
    if (generic_fields_tbl_ != NULL) {
        cb(generic_fields_tbl_, arg);
    }
}
 
void
rb_field_foreach(VALUE obj, rb_ivar_foreach_callback_func *func, st_data_t arg, bool ivar_only)
{
    if (SPECIAL_CONST_P(obj)) return;
    switch (BUILTIN_TYPE(obj)) {
      case T_IMEMO:
        if (IMEMO_TYPE_P(obj, imemo_fields)) {
            imemo_fields_each(obj, func, arg, ivar_only);
        }
        break;
      case T_OBJECT:
        obj_fields_each(obj, func, arg, ivar_only);
        break;
      case T_CLASS:
      case T_MODULE:
        {
            // No owner check: every caller of this walk uses the names only for a
            // class/module.  Values are checked where they are read (rb_ivar_lookup).
            VALUE fields_obj = RCLASS_WRITABLE_FIELDS_OBJ(obj);
            if (fields_obj) {
                imemo_fields_each(fields_obj, func, arg, ivar_only);
            }
        }
        break;
      default:
        {
            VALUE fields_obj = rb_obj_fields_no_ractor_check(obj);
            if (fields_obj) {
                imemo_fields_each(fields_obj, func, arg, ivar_only);
            }
        }
        break;
    }
}
 
struct ivar_buf_entry {
    ID name;
    VALUE val;
};
 
static int
collect_ivar_i(ID id, VALUE val, st_data_t arg)
{
    struct ivar_buf_entry **pos = (struct ivar_buf_entry **)arg;
    (*pos)->name = id;
    (*pos)->val = val;
    (*pos)++;
    return ST_CONTINUE;
}
 
void
rb_ivar_foreach(VALUE obj, rb_ivar_foreach_callback_func *func, st_data_t arg)
{
    rb_field_foreach(obj, func, arg, true);
}
 
void
rb_ivar_foreach_buffered(VALUE obj, rb_ivar_foreach_callback_func *func, st_data_t arg)
{
    st_index_t count = rb_ivar_count(obj);
    if (count == 0) return;
 
    VALUE tmpbuf;
    struct ivar_buf_entry *buf = ALLOCV_N(struct ivar_buf_entry, tmpbuf, count);
    struct ivar_buf_entry *pos = buf;
 
    rb_field_foreach(obj, collect_ivar_i, (st_data_t)&pos, true);
    RUBY_ASSERT((st_index_t)(pos - buf) == count);
 
    for (st_index_t i = 0; i < count; i++) {
        if (func(buf[i].name, buf[i].val, arg) == ST_STOP) break;
    }
 
    ALLOCV_END(tmpbuf);
}
 
st_index_t
rb_ivar_count(VALUE obj)
{
    if (SPECIAL_CONST_P(obj)) return 0;
 
    st_index_t iv_count = 0;
    VALUE fields_obj = rb_obj_fields_no_ractor_check(obj);
 
    if (fields_obj) {
        if (rb_obj_shape_complex_p(fields_obj)) {
            iv_count = rb_st_table_size(rb_imemo_fields_complex_tbl(fields_obj));
        }
        else {
            iv_count = RBASIC_FIELDS_COUNT(obj);
        }
    }
 
    if (rb_obj_shape_has_id(obj)) {
        iv_count--;
    }
 
    return iv_count;
}
 
static int
ivar_i(ID key, VALUE v, st_data_t a)
{
    VALUE ary = (VALUE)a;
 
    if (rb_is_instance_id(key)) {
        rb_ary_push(ary, ID2SYM(key));
    }
    return ST_CONTINUE;
}
 
/*
 *  call-seq:
 *     obj.instance_variables    -> array
 *
 *  Returns an array of instance variable names for the receiver. Note
 *  that simply defining an accessor does not create the corresponding
 *  instance variable.
 *
 *     class Fred
 *       attr_accessor :a1
 *       def initialize
 *         @iv = 3
 *       end
 *     end
 *     Fred.new.instance_variables   #=> [:@iv]
 */
 
VALUE
rb_obj_instance_variables(VALUE obj)
{
    VALUE ary = rb_ary_new_capa(rb_ivar_count(obj));
    rb_ivar_foreach(obj, ivar_i, ary);
    return ary;
}
 
#define rb_is_constant_id rb_is_const_id
#define rb_is_constant_name rb_is_const_name
#define id_for_var(obj, name, part, type) \
    id_for_var_message(obj, name, type, "'%1$s' is not allowed as "#part" "#type" variable name")
#define id_for_var_message(obj, name, type, message) \
    check_id_type(obj, &(name), rb_is_##type##_id, rb_is_##type##_name, message, strlen(message))
static ID
check_id_type(VALUE obj, VALUE *pname,
              int (*valid_id_p)(ID), int (*valid_name_p)(VALUE),
              const char *message, size_t message_len)
{
    ID id = rb_check_id(pname);
    VALUE name = *pname;
 
    if (id ? !valid_id_p(id) : !valid_name_p(name)) {
        rb_name_err_raise_str(rb_fstring_new(message, message_len),
                              obj, name);
    }
    return id;
}
 
/*
 *  call-seq:
 *     obj.remove_instance_variable(symbol)    -> obj
 *     obj.remove_instance_variable(string)    -> obj
 *
 *  Removes the named instance variable from <i>obj</i>, returning that
 *  variable's value. The name can be passed as a symbol or as a string.
 *
 *     class Dummy
 *       attr_reader :var
 *       def initialize
 *         @var = 99
 *       end
 *       def remove
 *         remove_instance_variable(:@var)
 *       end
 *     end
 *     d = Dummy.new
 *     d.var      #=> 99
 *     d.remove   #=> 99
 *     d.var      #=> nil
 */
 
VALUE
rb_obj_remove_instance_variable(VALUE obj, VALUE name)
{
    const ID id = id_for_var(obj, name, an, instance);
 
    // Frozen check comes here because it's expected that we raise a
    // NameError (from the id_for_var check) before we raise a FrozenError
    rb_check_frozen(obj);
 
    if (id) {
        VALUE val = rb_ivar_delete(obj, id, Qundef);
 
        if (!UNDEF_P(val)) return val;
    }
 
    rb_name_err_raise("instance variable %1$s not defined",
                      obj, name);
    UNREACHABLE_RETURN(Qnil);
}
 
NORETURN(static void uninitialized_constant(VALUE, VALUE));
static void
uninitialized_constant(VALUE klass, VALUE name)
{
    if (klass && rb_class_real(klass) != rb_cObject)
        rb_name_err_raise("uninitialized constant %2$s::%1$s",
                          klass, name);
    else
        rb_name_err_raise("uninitialized constant %1$s",
                          klass, name);
}
 
VALUE
rb_const_missing(VALUE klass, VALUE name)
{
    VALUE value = rb_funcallv(klass, idConst_missing, 1, &name);
    rb_vm_inc_const_missing_count();
    return value;
}
 
 
/*
 * call-seq:
 *    mod.const_missing(sym)    -> obj
 *
 * Invoked when a reference is made to an undefined constant in
 * <i>mod</i>. It is passed a symbol for the undefined constant, and
 * returns a value to be used for that constant. For example, consider:
 *
 *   def Foo.const_missing(name)
 *     name # return the constant name as Symbol
 *   end
 *
 *   Foo::UNDEFINED_CONST    #=> :UNDEFINED_CONST: symbol returned
 *
 * As the example above shows, +const_missing+ is not required to create the
 * missing constant in <i>mod</i>, though that is often a side-effect. The
 * caller gets its return value when triggered. If the constant is also defined,
 * further lookups won't hit +const_missing+ and will return the value stored in
 * the constant as usual. Otherwise, +const_missing+ will be invoked again.
 *
 * In the next example, when a reference is made to an undefined constant,
 * +const_missing+ attempts to load a file whose path is the lowercase version
 * of the constant name (thus class <code>Fred</code> is assumed to be in file
 * <code>fred.rb</code>). If defined as a side-effect of loading the file, the
 * method returns the value stored in the constant. This implements an autoload
 * feature similar to Kernel#autoload and Module#autoload, though it differs in
 * important ways.
 *
 *   def Object.const_missing(name)
 *     @looked_for ||= {}
 *     str_name = name.to_s
 *     raise "Constant not found: #{name}" if @looked_for[str_name]
 *     @looked_for[str_name] = 1
 *     file = str_name.downcase
 *     require file
 *     const_get(name, false)
 *   end
 *
 */
 
VALUE
rb_mod_const_missing(VALUE klass, VALUE name)
{
    rb_execution_context_t *ec = GET_EC();
    VALUE ref = ec->private_const_reference;
    rb_vm_pop_cfunc_frame();
    if (ref) {
        ec->private_const_reference = 0;
        rb_name_err_raise("private constant %2$s::%1$s referenced", ref, name);
    }
    uninitialized_constant(klass, name);
 
    UNREACHABLE_RETURN(Qnil);
}
 
// Every autoload constant has exactly one instance of autoload_const, stored in `autoload_features`. Since multiple autoload constants can refer to the same file, every `autoload_const` refers to a de-duplicated `autoload_data`.
struct autoload_const {
    // The linked list node of all constants which are loaded by the related autoload feature.
    struct ccan_list_node cnode; /* <=> autoload_data.constants */
 
    // The shared "autoload_data" if multiple constants are defined from the same feature.
    VALUE autoload_data_value;
 
    // The box object when the autoload is called in a user box
    // Otherwise, Qnil means the root box
    VALUE box_value;
 
    // The module we are loading a constant into.
    VALUE module;
 
    // The file that called autoload
    VALUE autoload_call_file;
 
    // The name of the constant we are loading.
    ID name;
 
    // The value of the constant (after it's loaded).
    VALUE value;
 
    // The constant entry flags which need to be re-applied after autoloading the feature.
    rb_const_flag_t flag;
 
    // The source file and line number that defined this constant (different from feature path).
    VALUE file;
    int line;
};
 
// Each `autoload_data` uniquely represents a specific feature which can be loaded, and a list of constants which it is able to define. We use a mutex to coordinate multiple threads trying to load the same feature.
struct autoload_data {
    // The feature path to require to load this constant.
    VALUE feature;
 
    // The mutex which is protecting autoloading this feature.
    VALUE mutex;
 
    // The process fork serial number since the autoload mutex will become invalid on fork.
    rb_serial_t fork_gen;
 
    // The linked list of all constants that are going to be loaded by this autoload.
    struct ccan_list_head constants; /* <=> autoload_const.cnode */
};
 
static void
autoload_data_mark_and_move(void *ptr)
{
    struct autoload_data *p = ptr;
 
    rb_gc_mark_and_move(&p->feature);
    rb_gc_mark_and_move(&p->mutex);
}
 
static void
autoload_data_free(void *ptr)
{
    struct autoload_data *p = ptr;
 
    struct autoload_const *autoload_const, *next;
    ccan_list_for_each_safe(&p->constants, autoload_const, next, cnode) {
        ccan_list_del_init(&autoload_const->cnode);
    }
 
    SIZED_FREE(p);
}
 
static size_t
autoload_data_memsize(const void *ptr)
{
    return sizeof(struct autoload_data);
}
 
static const rb_data_type_t autoload_data_type = {
    "autoload_data",
    {autoload_data_mark_and_move, autoload_data_free, autoload_data_memsize, autoload_data_mark_and_move},
    0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED
};
 
static void
autoload_const_mark_and_move(void *ptr)
{
    struct autoload_const *ac = ptr;
 
    rb_gc_mark_and_move(&ac->module);
    rb_gc_mark_and_move(&ac->autoload_call_file);
    rb_gc_mark_and_move(&ac->autoload_data_value);
    rb_gc_mark_and_move(&ac->value);
    rb_gc_mark_and_move(&ac->file);
    rb_gc_mark_and_move(&ac->box_value);
}
 
static size_t
autoload_const_memsize(const void *ptr)
{
    return sizeof(struct autoload_const);
}
 
static void
autoload_const_free(void *ptr)
{
    struct autoload_const *autoload_const = ptr;
 
    ccan_list_del(&autoload_const->cnode);
    SIZED_FREE(autoload_const);
}
 
static const rb_data_type_t autoload_const_type = {
    "autoload_const",
    {autoload_const_mark_and_move, autoload_const_free, autoload_const_memsize, autoload_const_mark_and_move,},
    0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED
};
 
static struct autoload_data *
get_autoload_data(VALUE autoload_const_value, struct autoload_const **autoload_const_pointer)
{
    struct autoload_const *autoload_const = rb_check_typeddata(autoload_const_value, &autoload_const_type);
 
    VALUE autoload_data_value = autoload_const->autoload_data_value;
    struct autoload_data *autoload_data = rb_check_typeddata(autoload_data_value, &autoload_data_type);
 
    /* do not reach across stack for ->state after forking: */
    if (autoload_data && autoload_data->fork_gen != GET_VM()->fork_gen) {
        RB_OBJ_WRITE(autoload_data_value, &autoload_data->mutex, Qnil);
        autoload_data->fork_gen = 0;
    }
 
    if (autoload_const_pointer) *autoload_const_pointer = autoload_const;
 
    return autoload_data;
}
 
// The autoload entry of the constant `id` of `mod`, or 0.
static VALUE
autoload_entry(VALUE mod, ID id)
{
    rb_const_entry_t *ce = rb_const_lookup(mod, id);
    if (!ce || !UNDEF_P(ce->value)) return 0;
    VM_ASSERT(rb_typeddata_is_kind_of(ce->u.autoload_const, &autoload_const_type));
    return ce->u.autoload_const;
}
 
 
static void const_set(VALUE klass, ID id, VALUE val);
static void const_added(VALUE klass, ID const_name);
 
struct autoload_arguments {
    VALUE module;
    ID name;
    VALUE feature;
    VALUE box_value;
};
 
static VALUE
autoload_feature_lookup_or_create(VALUE feature, struct autoload_data **autoload_data_pointer)
{
    RUBY_ASSERT_MUTEX_OWNED(autoload_mutex);
    RUBY_ASSERT_CRITICAL_SECTION_ENTER();
 
    VALUE autoload_data_value = rb_hash_aref(autoload_features, feature);
    struct autoload_data *autoload_data;
 
    if (NIL_P(autoload_data_value)) {
        autoload_data_value = TypedData_Make_Struct(0, struct autoload_data, &autoload_data_type, autoload_data);
        RB_OBJ_WRITE(autoload_data_value, &autoload_data->feature, feature);
        RB_OBJ_WRITE(autoload_data_value, &autoload_data->mutex, Qnil);
        ccan_list_head_init(&autoload_data->constants);
 
        if (autoload_data_pointer) *autoload_data_pointer = autoload_data;
 
        rb_hash_aset(autoload_features, feature, autoload_data_value);
    }
    else if (autoload_data_pointer) {
        *autoload_data_pointer = rb_check_typeddata(autoload_data_value, &autoload_data_type);
    }
 
    RUBY_ASSERT_CRITICAL_SECTION_LEAVE();
    return autoload_data_value;
}
 
static VALUE
autoload_synchronized(VALUE _arguments)
{
    struct autoload_arguments *arguments = (struct autoload_arguments *)_arguments;
 
    rb_const_entry_t *constant_entry = rb_const_lookup(arguments->module, arguments->name);
    if (constant_entry && !UNDEF_P(constant_entry->value)) {
        return Qfalse;
    }
 
    // Reset any state associated with any previous constant:
    const_set(arguments->module, arguments->name, Qundef);
    constant_entry = rb_const_lookup(arguments->module, arguments->name);
 
    // Ensure the string is uniqued since we use an identity lookup:
    VALUE feature = rb_fstring(arguments->feature);
 
    struct autoload_data *autoload_data;
    VALUE autoload_data_value = autoload_feature_lookup_or_create(feature, &autoload_data);
 
    {
        struct autoload_const *autoload_const;
        VALUE autoload_const_value = TypedData_Make_Struct(0, struct autoload_const, &autoload_const_type, autoload_const);
        RB_OBJ_WRITE(autoload_const_value, &autoload_const->box_value, arguments->box_value);
        RB_OBJ_WRITE(autoload_const_value, &autoload_const->module, arguments->module);
        RB_OBJ_WRITE(autoload_const_value, &autoload_const->autoload_call_file, constant_entry->u.file);
        autoload_const->name = arguments->name;
        autoload_const->value = Qundef;
        autoload_const->flag = CONST_PUBLIC;
        RB_OBJ_WRITE(autoload_const_value, &autoload_const->autoload_data_value, autoload_data_value);
        ccan_list_add_tail(&autoload_data->constants, &autoload_const->cnode);
        RB_OBJ_WRITE(arguments->module, &constant_entry->u.autoload_const, autoload_const_value);
    }
 
    return Qtrue;
}
 
void
rb_autoload_str(VALUE module, ID name, VALUE feature)
{
    const rb_box_t *box = rb_current_box();
    VALUE current_box_value = rb_get_box_object((rb_box_t *)box);
 
    if (!rb_is_const_id(name)) {
        rb_raise(rb_eNameError, "autoload must be constant name: %"PRIsVALUE"", QUOTE_ID(name));
    }
 
    rb_class_owner_check(module);
 
    Check_Type(feature, T_STRING);
    if (!RSTRING_LEN(feature)) {
        rb_raise(rb_eArgError, "empty feature name");
    }
 
    struct autoload_arguments arguments = {
        .module = module,
        .name = name,
        .feature = feature,
        .box_value = current_box_value,
    };
 
    VALUE result = rb_mutex_synchronize(autoload_mutex, autoload_synchronized, (VALUE)&arguments);
 
    if (result == Qtrue) {
        const_added(module, name);
    }
}
 
static void
autoload_delete(VALUE autoload_const_value)
{
    RUBY_ASSERT_CRITICAL_SECTION_ENTER();
 
    VM_ASSERT(rb_typeddata_is_kind_of(autoload_const_value, &autoload_const_type));
 
    struct autoload_const *autoload_const;
    struct autoload_data *autoload_data = get_autoload_data(autoload_const_value, &autoload_const);
 
    VM_ASSERT(autoload_data);
 
    /*
     * we must delete here to avoid "already initialized" warnings
     * with parallel autoload.  Using list_del_init here so list_del
     * works in autoload_const_free
     */
    ccan_list_del_init(&autoload_const->cnode);
 
    if (ccan_list_empty(&autoload_data->constants)) {
        rb_hash_delete(autoload_features, autoload_data->feature);
    }
 
    RUBY_ASSERT_CRITICAL_SECTION_LEAVE();
}
 
static int
autoload_by_someone_else(struct autoload_data *ele)
{
    return ele->mutex != Qnil && RTEST(rb_mutex_locked_p(ele->mutex)) && !rb_mutex_owned_p(ele->mutex);
}
 
static VALUE
check_autoload_required(VALUE mod, ID id, const char **loadingpath)
{
    VALUE autoload_const_value = autoload_entry(mod, id);
    struct autoload_data *autoload_data;
    const char *loading;
 
    if (!autoload_const_value || !(autoload_data = get_autoload_data(autoload_const_value, 0))) {
        return 0;
    }
 
    VALUE feature = autoload_data->feature;
 
    /*
     * if somebody else is autoloading, we MUST wait for them, since
     * rb_provide_feature can provide a feature before autoload_const_set
     * completes.  We must wait until autoload_const_set finishes in
     * the other thread.
     */
    if (autoload_by_someone_else(autoload_data)) {
        return autoload_const_value;
    }
 
    loading = RSTRING_PTR(feature);
 
    if (!rb_feature_provided(loading, &loading)) {
        return autoload_const_value;
    }
 
    if (loadingpath && loading) {
        *loadingpath = loading;
        return autoload_const_value;
    }
 
    return 0;
}
 
static struct autoload_const *autoloading_const_entry(VALUE mod, ID id);
 
int
rb_autoloading_value(VALUE mod, ID id, VALUE* value, rb_const_flag_t *flag)
{
    struct autoload_const *ac = autoloading_const_entry(mod, id);
    if (!ac) return FALSE;
 
    if (value) {
        *value = ac->value;
    }
 
    if (flag) {
        *flag = ac->flag;
    }
 
    return TRUE;
}
 
static int
autoload_by_current(struct autoload_data *ele)
{
    return ele->mutex != Qnil && rb_mutex_owned_p(ele->mutex);
}
 
// If there is an autoloading constant and it has been set by the current
// execution context, return it. This allows threads which are loading code to
// refer to their own autoloaded constants.
struct autoload_const *
autoloading_const_entry(VALUE mod, ID id)
{
    VALUE load = autoload_entry(mod, id);
    struct autoload_data *ele;
    struct autoload_const *ac;
 
    // Find the autoloading state:
    if (!load || !(ele = get_autoload_data(load, &ac))) {
        // Couldn't be found:
        return 0;
    }
 
    // Check if it's being loaded by the current thread/fiber:
    if (autoload_by_current(ele)) {
        if (!UNDEF_P(ac->value)) {
            return ac;
        }
    }
 
    return 0;
}
 
static int
autoload_defined_p(VALUE mod, ID id)
{
    rb_const_entry_t *ce = rb_const_lookup(mod, id);
 
    // If there is no constant or the constant is not undefined (special marker for autoloading):
    if (!ce || !UNDEF_P(ce->value)) {
        // We are not autoloading:
        return 0;
    }
 
    // Otherwise check if there is an autoload in flight right now:
    return !rb_autoloading_value(mod, id, NULL, NULL);
}
 
/* const_tbl_update() runs under the VM lock, where it can neither warn nor
 * build the message: rb_warn() dispatches Warning.warn and writes to $stderr,
 * and formatting a "%"PRIsVALUE" calls #to_s.  It records what to warn about
 * instead, and the caller warns once the lock is released. */
struct const_warning {
    ID id; /* 0 when there is nothing to warn about */
    VALUE module;
    VALUE file;
    int line;
};
 
static void const_tbl_update(struct autoload_const *, int, struct const_warning *);
 
static void
const_warning_emit(const struct const_warning *warning)
{
    if (!warning->id) return;
 
    VALUE name = QUOTE_ID(warning->id);
    VALUE previous = Qnil;
 
    if (!NIL_P(warning->file) && warning->line) {
        previous = rb_sprintf("\n%"PRIsVALUE":%d: warning: previous definition of %"PRIsVALUE" was here",
                              warning->file, warning->line, name);
    }
 
    if (warning->module == rb_cObject) {
        rb_warn("already initialized constant %"PRIsVALUE"%"PRIsVALUE"", name, previous);
    }
    else {
        rb_warn("already initialized constant %"PRIsVALUE"::%"PRIsVALUE"%"PRIsVALUE"",
                rb_class_name(warning->module), name, previous);
    }
}
 
struct autoload_load_arguments {
    VALUE module;
    ID name;
    int flag;
 
    VALUE mutex;
 
    // The specific constant which triggered the autoload code to fire:
    struct autoload_const *autoload_const;
 
    // The parent autoload data which is shared between multiple constants:
    struct autoload_data *autoload_data;
};
 
static VALUE
autoload_const_set(struct autoload_const *ac)
{
    check_before_mod_set(ac->module, ac->name, ac->value, "constant");
 
    struct const_warning warning = {0};
    RB_VM_LOCKING() {
        const_tbl_update(ac, true, &warning);
    }
    const_warning_emit(&warning);
 
    return 0; /* ignored */
}
 
static VALUE
autoload_load_needed(VALUE _arguments)
{
    struct autoload_load_arguments *arguments = (struct autoload_load_arguments*)_arguments;
 
    const char *loading = 0, *src;
 
    if (!autoload_defined_p(arguments->module, arguments->name)) {
        return Qfalse;
    }
 
    VALUE autoload_const_value = check_autoload_required(arguments->module, arguments->name, &loading);
    if (!autoload_const_value) {
        return Qfalse;
    }
 
    src = rb_sourcefile();
    if (src && loading && strcmp(src, loading) == 0) {
        return Qfalse;
    }
 
    struct autoload_const *autoload_const;
    struct autoload_data *autoload_data;
    if (!(autoload_data = get_autoload_data(autoload_const_value, &autoload_const))) {
        return Qfalse;
    }
 
    if (NIL_P(autoload_data->mutex)) {
        RB_OBJ_WRITE(autoload_const->autoload_data_value, &autoload_data->mutex, rb_mutex_new());
        autoload_data->fork_gen = GET_VM()->fork_gen;
    }
    else if (rb_mutex_owned_p(autoload_data->mutex)) {
        return Qfalse;
    }
 
    arguments->mutex = autoload_data->mutex;
    arguments->autoload_const = autoload_const;
 
    return autoload_const_value;
}
 
static VALUE
autoload_apply_constants(VALUE _arguments)
{
    RUBY_ASSERT_CRITICAL_SECTION_ENTER();
 
    struct autoload_load_arguments *arguments = (struct autoload_load_arguments*)_arguments;
 
    struct autoload_const *autoload_const = 0; // for ccan_container_off_var()
    struct autoload_const *next;
 
    // We use safe iteration here because `autoload_const_set` will eventually invoke
    // `autoload_delete` which will remove the constant from the linked list. In theory, once
    // the `autoload_data->constants` linked list is empty, we can remove it.
 
    // Iterate over all constants and assign them:
    ccan_list_for_each_safe(&arguments->autoload_data->constants, autoload_const, next, cnode) {
        if (!UNDEF_P(autoload_const->value)) {
            autoload_const_set(autoload_const);
        }
    }
 
    RUBY_ASSERT_CRITICAL_SECTION_LEAVE();
 
    return Qtrue;
}
 
// Require the feature and set the constants of the autoload.
static VALUE
autoload_require_and_apply(VALUE receiver, VALUE _arguments)
{
    struct autoload_load_arguments *arguments = (struct autoload_load_arguments*)_arguments;
 
    VALUE result = rb_funcall(receiver, rb_intern("require"), 1, arguments->autoload_data->feature);
    if (RTEST(result)) {
        return rb_mutex_synchronize(autoload_mutex, autoload_apply_constants, _arguments);
    }
    return result;
}
 
static VALUE
autoload_feature_require_in_box(VALUE receiver, VALUE _arguments)
{
    rb_vm_frame_flag_set_box_require(GET_EC());
 
    return autoload_require_and_apply(receiver, _arguments);
}
 
static VALUE
autoload_feature_require(VALUE _arguments)
{
    struct autoload_load_arguments *arguments = (struct autoload_load_arguments*)_arguments;
 
    struct autoload_const *autoload_const = arguments->autoload_const;
    VALUE autoload_box_value = autoload_const->box_value;
 
    // We save this for later use in autoload_apply_constants:
    arguments->autoload_data = rb_check_typeddata(autoload_const->autoload_data_value, &autoload_data_type);
 
    /*
     * Clear the global cc cache table because the require method can be different from the current
     * box's one and it may cause inconsistent cc-cme states.
     * For example, the assertion below may fail in gccct_method_search();
     * VM_ASSERT(vm_cc_check_cme(cc, rb_callable_method_entry(klass, mid)))
     */
    rb_gccct_clear_table();
 
    VALUE feature = arguments->autoload_data->feature;
    rb_box_t *box = NULL;
    if (rb_box_available() && BOX_OBJ_P(autoload_box_value)) {
        box = rb_get_box_t(autoload_box_value);
    }
 
    if (box && box->top_self) {
        /*
         * Call `require` on the top self of the box that registered the autoload, in a frame
         * running in that box, so that `Kernel#require` decorations in the box (RubyGems,
         * Zeitwerk, etc.) are dispatched and the feature is loaded into that box.
         */
        return rb_vm_call_cfunc_in_box(box->top_self, autoload_feature_require_in_box,
                                       box->top_self, _arguments, feature, box);
    }
    return autoload_require_and_apply(rb_vm_top_self(), _arguments);
}
 
static rb_const_entry_t *const_lookup(struct rb_id_table *tbl, ID id);
 
// The box in which the feature of the autoload is required.
static const rb_box_t *
autoload_box(const struct autoload_const *ac)
{
    if (rb_box_available() && BOX_OBJ_P(ac->box_value)) {
        const rb_box_t *box = rb_get_box_t(ac->box_value);
        if (box->top_self) return box;
    }
    return rb_current_box();
}
 
// The constant entry `id` of `mod` in the view of `box`.
static rb_const_entry_t *
const_lookup_in_box(VALUE mod, ID id, const rb_box_t *box)
{
    return const_lookup(RCLASSEXT_CONST_TBL(RCLASS_EXT_READABLE_IN_BOX(mod, box)), id);
}
 
static VALUE
autoload_try_load(VALUE _arguments)
{
    struct autoload_load_arguments *arguments = (struct autoload_load_arguments*)_arguments;
 
    // Load the feature and set the constants in the box that registered the autoload:
    VALUE result = autoload_feature_require(_arguments);
 
    // After we loaded the feature, if the constant is not defined, we remove it completely:
    rb_const_entry_t *ce = rb_const_lookup(arguments->module, arguments->name);
 
    // Copy the constant from the box that registered the autoload into the current box.
    // E.g., after a box B1 triggers the autoload, another box B2 with its own copy of the
    // module still has it; referring to it in B2 comes here too, as the require does nothing.
    if (ce && UNDEF_P(ce->value)) {
        rb_const_entry_t *loaded = const_lookup_in_box(arguments->module, arguments->name,
                                                       autoload_box(arguments->autoload_const));
        if (loaded && !UNDEF_P(loaded->value)) {
            RB_VM_LOCKING() {
                ce->flag = loaded->flag;
                RB_OBJ_WRITE(arguments->module, &ce->value, loaded->value);
                RB_OBJ_WRITE(arguments->module, &ce->u.file, loaded->u.file);
                ce->line = loaded->line;
                rb_clear_constant_cache_for_id(arguments->name);
            }
            result = Qtrue;
        }
    }
 
    if (!ce || UNDEF_P(ce->value)) {
        result = Qfalse;
 
        rb_const_remove(arguments->module, arguments->name);
 
        if (arguments->module == rb_cObject) {
            rb_warning(
                "Expected %"PRIsVALUE" to define %"PRIsVALUE" but it didn't",
                arguments->autoload_data->feature,
                ID2SYM(arguments->name)
            );
        }
        else {
            rb_warning(
                "Expected %"PRIsVALUE" to define %"PRIsVALUE"::%"PRIsVALUE" but it didn't",
                arguments->autoload_data->feature,
                arguments->module,
                ID2SYM(arguments->name)
            );
        }
    }
    else {
        // Otherwise, it was loaded, copy the flags from the autoload constant:
        ce->flag |= arguments->flag;
    }
 
    return result;
}
 
VALUE
rb_autoload_load(VALUE module, ID name)
{
    rb_const_entry_t *ce = rb_const_lookup(module, name);
 
    // We bail out as early as possible without any synchronisation:
    if (!ce || !UNDEF_P(ce->value)) {
        return Qfalse;
    }
 
    // At this point, we assume there might be autoloading, so fail if it's ractor:
    if (UNLIKELY(!rb_ractor_main_p())) {
        return rb_ractor_autoload_load(module, name);
    }
 
    // This state is stored on the stack and is used during the autoload process.
    struct autoload_load_arguments arguments = {.module = module, .name = name, .mutex = Qnil};
 
    // Figure out whether we can autoload the named constant:
    VALUE autoload_const_value = rb_mutex_synchronize(autoload_mutex, autoload_load_needed, (VALUE)&arguments);
 
    // This confirms whether autoloading is required or not:
    if (autoload_const_value == Qfalse) return autoload_const_value;
 
    arguments.flag = ce->flag & (CONST_DEPRECATED | CONST_VISIBILITY_MASK);
 
    // Only one thread will enter here at a time:
    VALUE result = rb_mutex_synchronize(arguments.mutex, autoload_try_load, (VALUE)&arguments);
 
    // If you don't guard this value, it's possible for the autoload constant to
    // be freed by another thread which loads multiple constants, one of which
    // resolves to the constant this thread is trying to load, so proteect this
    // so that it is not freed until we are done with it in `autoload_try_load`:
    RB_GC_GUARD(autoload_const_value);
 
    return result;
}
 
VALUE
rb_autoload_p(VALUE mod, ID id)
{
    return rb_autoload_at_p(mod, id, TRUE);
}
 
VALUE
rb_autoload_at_p(VALUE mod, ID id, int recur)
{
    VALUE load;
    struct autoload_data *ele;
 
    while (!autoload_defined_p(mod, id)) {
        if (!recur) return Qnil;
        mod = RCLASS_SUPER(mod);
        if (!mod) return Qnil;
    }
    load = check_autoload_required(mod, id, 0);
    if (!load) return Qnil;
    return (ele = get_autoload_data(load, 0)) ? ele->feature : Qnil;
}
 
void
rb_const_warn_if_deprecated(const rb_const_entry_t *ce, VALUE klass, ID id)
{
    if (RB_CONST_DEPRECATED_P(ce) &&
        rb_warning_category_enabled_p(RB_WARN_CATEGORY_DEPRECATED)) {
        if (klass == rb_cObject) {
            rb_category_warn(RB_WARN_CATEGORY_DEPRECATED, "constant ::%"PRIsVALUE" is deprecated", QUOTE_ID(id));
        }
        else {
            rb_category_warn(RB_WARN_CATEGORY_DEPRECATED, "constant %"PRIsVALUE"::%"PRIsVALUE" is deprecated",
                    rb_class_name(klass), QUOTE_ID(id));
        }
    }
}
 
void
rb_const_unshareable_error(VALUE klass, ID id)
{
    rb_raise(rb_eRactorIsolationError, "can not access non-shareable objects in constant %"PRIsVALUE"::%"PRIsVALUE" of a class/module created by another Ractor.", rb_class_path(klass), rb_id2str(id));
}
 
static VALUE
rb_const_get_0(VALUE klass, ID id, int exclude, int recurse, int visibility)
{
    VALUE found_in;
    VALUE c = rb_const_search(klass, id, exclude, recurse, visibility, &found_in);
    if (!UNDEF_P(c)) {
        return c; // rb_const_search_from checked a foreign class's value
    }
    return rb_const_missing(klass, ID2SYM(id));
}
 
static VALUE
rb_const_search_from(VALUE klass, ID id, int exclude, int recurse, int visibility, VALUE *found_in)
{
    VALUE value, current;
    bool first_iteration = true;
 
    for (current = klass;
            RTEST(current);
            current = RCLASS_SUPER(current), first_iteration = false) {
        VALUE tmp;
        VALUE am = 0;
        rb_const_entry_t entry, *ce = &entry;
 
        if (!first_iteration && RCLASS_ORIGIN(current) != current) {
            // This item in the super chain has an origin iclass
            // that comes later in the chain. Skip this item so
            // prepended modules take precedence.
            continue;
        }
 
        // Do lookup in original class or module in case we are at an origin
        // iclass in the chain.
        tmp = current;
        if (BUILTIN_TYPE(tmp) == T_ICLASS) tmp = RBASIC(tmp)->klass;
 
        // Do the lookup. Loop in case of autoload.
        while (rb_const_lookup_copy(tmp, id, ce)) {
            if (visibility && RB_CONST_PRIVATE_P(ce)) {
                GET_EC()->private_const_reference = tmp;
                return Qundef;
            }
            value = ce->value;
            // before the warning, which may run Ruby: only this stack holds value until the owner has it
            if (!UNDEF_P(value) && UNLIKELY(!rb_class_owned_p(tmp)) && !rb_class_field_shareable_p(tmp, value)) {
                rb_const_warn_if_deprecated(ce, tmp, id);
                rb_const_unshareable_error(tmp, id);
            }
            rb_const_warn_if_deprecated(ce, tmp, id);
            if (UNDEF_P(value)) {
                struct autoload_const *ac;
                if (am == tmp) break;
                am = tmp;
                ac = autoloading_const_entry(tmp, id);
                if (ac) {
                    if (found_in) { *found_in = tmp; }
                    if (UNLIKELY(!rb_class_owned_p(tmp)) && !rb_class_field_shareable_p(tmp, ac->value)) {
                        rb_const_unshareable_error(tmp, id);
                    }
                    return ac->value;
                }
                rb_autoload_load(tmp, id);
                continue;
            }
            if (exclude && tmp == rb_cObject) {
                goto not_found;
            }
            if (found_in) { *found_in = tmp; }
            return value;
        }
        if (!recurse) break;
    }
 
  not_found:
    GET_EC()->private_const_reference = 0;
    return Qundef;
}
 
static VALUE
rb_const_search(VALUE klass, ID id, int exclude, int recurse, int visibility, VALUE *found_in)
{
    VALUE value;
 
    if (klass == rb_cObject) exclude = FALSE;
    value = rb_const_search_from(klass, id, exclude, recurse, visibility, found_in);
    if (!UNDEF_P(value)) return value;
    if (exclude) return value;
    if (BUILTIN_TYPE(klass) != T_MODULE) return value;
    /* search global const too, if klass is a module */
    return rb_const_search_from(rb_cObject, id, FALSE, recurse, visibility, found_in);
}
 
VALUE
rb_const_get_from(VALUE klass, ID id)
{
    return rb_const_get_0(klass, id, TRUE, TRUE, FALSE);
}
 
VALUE
rb_const_get(VALUE klass, ID id)
{
    return rb_const_get_0(klass, id, FALSE, TRUE, FALSE);
}
 
VALUE
rb_const_get_at(VALUE klass, ID id)
{
    return rb_const_get_0(klass, id, TRUE, FALSE, FALSE);
}
 
VALUE
rb_public_const_get_from(VALUE klass, ID id)
{
    return rb_const_get_0(klass, id, TRUE, TRUE, TRUE);
}
 
VALUE
rb_public_const_get_at(VALUE klass, ID id)
{
    return rb_const_get_0(klass, id, TRUE, FALSE, TRUE);
}
 
NORETURN(static void undefined_constant(VALUE mod, VALUE name));
static void
undefined_constant(VALUE mod, VALUE name)
{
    rb_name_err_raise("constant %2$s::%1$s not defined",
                      mod, name);
}
 
static VALUE
rb_const_location_from(VALUE klass, ID id, int exclude, int recurse, int visibility)
{
    while (RTEST(klass)) {
        rb_const_entry_t entry, *ce = &entry;
 
        while (rb_const_lookup_copy(klass, id, ce)) {
            if (visibility && RB_CONST_PRIVATE_P(ce)) {
                return Qnil;
            }
            if (exclude && klass == rb_cObject) {
                goto not_found;
            }
 
            VALUE file = ce->u.file;
            VALUE autoload_const_value = autoload_entry(klass, id);
            if (autoload_const_value) {
                struct autoload_const *autoload_const;
                struct autoload_data *autoload_data = get_autoload_data(autoload_const_value, &autoload_const);
 
                if (!UNDEF_P(autoload_const->value) && RTEST(rb_mutex_owned_p(autoload_data->mutex))) {
                    return rb_assoc_new(autoload_const->file, INT2NUM(autoload_const->line));
                }
                file = autoload_const->autoload_call_file;
            }
 
            if (NIL_P(file)) return rb_ary_new();
            return rb_assoc_new(file, INT2NUM(ce->line));
        }
        if (!recurse) break;
        klass = RCLASS_SUPER(klass);
    }
 
  not_found:
    return Qnil;
}
 
static VALUE
rb_const_location(VALUE klass, ID id, int exclude, int recurse, int visibility)
{
    VALUE loc;
 
    if (klass == rb_cObject) exclude = FALSE;
    loc = rb_const_location_from(klass, id, exclude, recurse, visibility);
    if (!NIL_P(loc)) return loc;
    if (exclude) return loc;
    if (BUILTIN_TYPE(klass) != T_MODULE) return loc;
    /* search global const too, if klass is a module */
    return rb_const_location_from(rb_cObject, id, FALSE, recurse, visibility);
}
 
VALUE
rb_const_source_location(VALUE klass, ID id)
{
    return rb_const_location(klass, id, FALSE, TRUE, FALSE);
}
 
VALUE
rb_const_source_location_at(VALUE klass, ID id)
{
    return rb_const_location(klass, id, TRUE, FALSE, FALSE);
}
 
/*
 *  call-seq:
 *     remove_const(sym)   -> obj
 *
 *  Removes the definition of the given constant, returning that
 *  constant's previous value.  If that constant referred to
 *  a module, this will not change that module's name and can lead
 *  to confusion.
 */
 
VALUE
rb_mod_remove_const(VALUE mod, VALUE name)
{
    const ID id = id_for_var(mod, name, a, constant);
 
    if (!id) {
        undefined_constant(mod, name);
    }
    return rb_const_remove(mod, id);
}
 
static rb_const_entry_t * const_lookup(struct rb_id_table *tbl, ID id);
 
VALUE
rb_const_remove(VALUE mod, ID id)
{
    VALUE val;
    rb_const_entry_t *ce;
 
    rb_check_frozen(mod);
    rb_class_owner_check(mod);
 
    ce = rb_const_lookup(mod, id);
 
    if (!ce) {
        if (rb_const_defined_at(mod, id)) {
            rb_name_err_raise("cannot remove %2$s::%1$s", mod, ID2SYM(id));
        }
 
        undefined_constant(mod, ID2SYM(id));
    }
 
    VALUE writable_ce = 0;
    bool found;
    RB_VM_LOCKING() { // see rb_const_lookup_copy
        found = rb_id_table_lookup(RCLASS_WRITABLE_CONST_TBL(mod), id, &writable_ce);
        if (found) rb_id_table_delete(RCLASS_WRITABLE_CONST_TBL(mod), id);
    }
    if (found && (rb_const_entry_t *)writable_ce != ce) {
        SIZED_FREE((rb_const_entry_t *)writable_ce);
    }
 
    rb_const_warn_if_deprecated(ce, mod, id);
    rb_clear_constant_cache_for_id(id);
 
    val = ce->value;
 
    if (UNDEF_P(val)) {
        autoload_delete(ce->u.autoload_const);
        val = Qnil;
    }
 
    if (ce != const_lookup(RCLASS_PRIME_CONST_TBL(mod), id)) {
        SIZED_FREE(ce);
    }
    // else - skip free'ing the ce because it still exists in the prime classext
 
    return val;
}
 
static int
cv_i_update(st_data_t *k, st_data_t *v, st_data_t a, int existing)
{
    if (existing) return ST_STOP;
    *v = a;
    return ST_CONTINUE;
}
 
static enum rb_id_table_iterator_result
sv_i(ID key, VALUE v, void *a)
{
    rb_const_entry_t *ce = (rb_const_entry_t *)v;
    st_table *tbl = a;
 
    if (rb_is_const_id(key)) {
        st_update(tbl, (st_data_t)key, cv_i_update, (st_data_t)ce);
    }
    return ID_TABLE_CONTINUE;
}
 
static enum rb_id_table_iterator_result
rb_local_constants_i(ID const_name, VALUE const_value, void *ary)
{
    if (rb_is_const_id(const_name) && !RB_CONST_PRIVATE_P((rb_const_entry_t *)const_value)) {
        rb_ary_push((VALUE)ary, ID2SYM(const_name));
    }
    return ID_TABLE_CONTINUE;
}
 
static VALUE
rb_local_constants(VALUE mod)
{
    struct rb_id_table *tbl = RCLASS_CONST_TBL(mod);
    VALUE ary;
 
    if (!tbl) return rb_ary_new2(0);
 
    RB_VM_LOCKING() {
        ary = rb_ary_new2(rb_id_table_size(tbl));
        rb_id_table_foreach(tbl, rb_local_constants_i, (void *)ary);
    }
 
    return ary;
}
 
void*
rb_mod_const_at(VALUE mod, void *data)
{
    st_table *tbl = data;
    if (!tbl) {
        tbl = st_init_numtable();
    }
    if (RCLASS_CONST_TBL(mod)) {
        RB_VM_LOCKING() {
            rb_id_table_foreach(RCLASS_CONST_TBL(mod), sv_i, tbl);
        }
    }
    return tbl;
}
 
void*
rb_mod_const_of(VALUE mod, void *data)
{
    VALUE tmp = mod;
    for (;;) {
        data = rb_mod_const_at(tmp, data);
        tmp = RCLASS_SUPER(tmp);
        if (!tmp) break;
        if (tmp == rb_cObject && mod != rb_cObject) break;
    }
    return data;
}
 
static int
list_i(st_data_t key, st_data_t value, VALUE ary)
{
    ID sym = (ID)key;
    rb_const_entry_t *ce = (rb_const_entry_t *)value;
    if (RB_CONST_PUBLIC_P(ce)) rb_ary_push(ary, ID2SYM(sym));
    return ST_CONTINUE;
}
 
VALUE
rb_const_list(void *data)
{
    st_table *tbl = data;
    VALUE ary;
 
    if (!tbl) return rb_ary_new2(0);
    ary = rb_ary_new2(tbl->num_entries);
    st_foreach_safe(tbl, list_i, ary);
    st_free_table(tbl);
 
    return ary;
}
 
/*
 *  call-seq:
 *     mod.constants(inherit=true)    -> array
 *
 *  Returns an array of the names of the constants accessible in
 *  <i>mod</i>. This includes the names of constants in any included
 *  modules (example at start of section), unless the <i>inherit</i>
 *  parameter is set to <code>false</code>.
 *
 *  The implementation makes no guarantees about the order in which the
 *  constants are yielded.
 *
 *    IO.constants.include?(:SYNC)        #=> true
 *    IO.constants(false).include?(:SYNC) #=> false
 *
 *  Also see Module#const_defined?.
 */
 
VALUE
rb_mod_constants(int argc, const VALUE *argv, VALUE mod)
{
    bool inherit = true;
 
    if (rb_check_arity(argc, 0, 1)) inherit = RTEST(argv[0]);
 
    if (inherit) {
        return rb_const_list(rb_mod_const_of(mod, 0));
    }
    else {
        return rb_local_constants(mod);
    }
}
 
static int
rb_const_defined_0(VALUE klass, ID id, int exclude, int recurse, int visibility)
{
    VALUE tmp;
    int mod_retry = 0;
    rb_const_entry_t entry, *ce = &entry;
 
    tmp = klass;
  retry:
    while (tmp) {
        if (rb_const_lookup_copy(tmp, id, ce)) {
            if (visibility && RB_CONST_PRIVATE_P(ce)) {
                return (int)Qfalse;
            }
            if (UNDEF_P(ce->value) && !check_autoload_required(tmp, id, 0) &&
                !rb_autoloading_value(tmp, id, NULL, NULL))
                return (int)Qfalse;
 
            if (exclude && tmp == rb_cObject && klass != rb_cObject) {
                return (int)Qfalse;
            }
 
            return (int)Qtrue;
        }
        if (!recurse) break;
        tmp = RCLASS_SUPER(tmp);
    }
    if (!exclude && !mod_retry && BUILTIN_TYPE(klass) == T_MODULE) {
        mod_retry = 1;
        tmp = rb_cObject;
        goto retry;
    }
    return (int)Qfalse;
}
 
int
rb_const_defined_from(VALUE klass, ID id)
{
    return rb_const_defined_0(klass, id, TRUE, TRUE, FALSE);
}
 
int
rb_const_defined(VALUE klass, ID id)
{
    return rb_const_defined_0(klass, id, FALSE, TRUE, FALSE);
}
 
int
rb_const_defined_at(VALUE klass, ID id)
{
    return rb_const_defined_0(klass, id, TRUE, FALSE, FALSE);
}
 
int
rb_public_const_defined_from(VALUE klass, ID id)
{
    return rb_const_defined_0(klass, id, TRUE, TRUE, TRUE);
}
 
static void
check_before_mod_set(VALUE klass, ID id, VALUE val, const char *dest)
{
    rb_check_frozen(klass);
}
 
static void set_namespace_path(VALUE named_namespace, VALUE name);
 
static enum rb_id_table_iterator_result
set_namespace_path_i(ID id, VALUE v, void *payload)
{
    rb_const_entry_t *ce = (rb_const_entry_t *)v;
    VALUE value = ce->value;
    VALUE parental_path = *((VALUE *) payload);
    if (!rb_is_const_id(id) || !rb_namespace_p(value)) {
        return ID_TABLE_CONTINUE;
    }
 
    bool has_permanent_classpath;
    classname(value, &has_permanent_classpath);
    if (has_permanent_classpath) {
        return ID_TABLE_CONTINUE;
    }
    set_namespace_path(value, build_const_path(parental_path, id));
 
    if (!RCLASS_PERMANENT_CLASSPATH_P(value)) {
        RCLASS_WRITE_CLASSPATH(value, 0, false);
    }
 
    return ID_TABLE_CONTINUE;
}
 
/*
 * Assign permanent classpaths to all namespaces that are directly or indirectly
 * nested under +named_namespace+. +named_namespace+ must have a permanent
 * classpath.
 */
static void
set_namespace_path(VALUE named_namespace, VALUE namespace_path)
{
    struct rb_id_table *const_table = RCLASS_CONST_TBL(named_namespace);
    RB_OBJ_SET_SHAREABLE(namespace_path);
 
    RB_VM_LOCKING() {
        RCLASS_WRITE_CLASSPATH(named_namespace, namespace_path, true);
 
        if (const_table) {
            rb_id_table_foreach(const_table, set_namespace_path_i, &namespace_path);
        }
    }
}
 
static void
const_added(VALUE klass, ID const_name)
{
    if (GET_VM()->running) {
        VALUE arg = ID2SYM(const_name);
        rb_funcallv_uncached(klass, idConst_added, 1, &arg);
    }
}
 
static void
const_set(VALUE klass, ID id, VALUE val)
{
    rb_const_entry_t *ce;
 
    if (NIL_P(klass)) {
        rb_raise(rb_eTypeError, "no class/module to define constant %"PRIsVALUE"",
                 QUOTE_ID(id));
    }
 
    if (UNLIKELY(!rb_class_owned_p(klass))) {
        rb_raise(rb_eRactorIsolationError, "can not set constants of classes/modules created by another Ractor");
    }
 
    check_before_mod_set(klass, id, val, "constant");
 
    struct const_warning warning = {0};
    RB_VM_LOCKING() {
        struct rb_id_table *tbl = RCLASS_WRITABLE_CONST_TBL(klass);
        if (!tbl) {
            tbl = rb_id_table_create(0);
            RCLASS_WRITE_CONST_TBL(klass, tbl, false);
            rb_clear_constant_cache_for_id(id);
            ce = ZALLOC(rb_const_entry_t);
            rb_id_table_insert(tbl, id, (VALUE)ce);
            setup_const_entry(ce, klass, val, CONST_PUBLIC);
        }
        else {
            struct autoload_const ac = {
                .module = klass, .name = id,
                .value = val, .flag = CONST_PUBLIC,
                /* fill the rest with 0 */
            };
            ac.file = rb_source_location(&ac.line);
            const_tbl_update(&ac, false, &warning);
        }
    }
    const_warning_emit(&warning);
 
    /*
     * Resolve and cache class name immediately to resolve ambiguity
     * and avoid order-dependency on const_tbl
     */
    if (rb_cObject && rb_namespace_p(val)) {
        bool val_path_permanent;
        VALUE val_path = classname(val, &val_path_permanent);
        if (NIL_P(val_path) || !val_path_permanent) {
            if (klass == rb_cObject) {
                set_namespace_path(val, rb_id2str(id));
            }
            else {
                bool parental_path_permanent;
                VALUE parental_path = classname(klass, &parental_path_permanent);
                if (NIL_P(parental_path)) {
                    bool throwaway;
                    parental_path = rb_tmp_class_path(klass, &throwaway, make_temporary_path);
                }
                if (parental_path_permanent && !val_path_permanent) {
                    set_namespace_path(val, build_const_path(parental_path, id));
                }
                else if (!parental_path_permanent && NIL_P(val_path)) {
                    VALUE path = build_const_path(parental_path, id);
                    RCLASS_SET_CLASSPATH(val, path, false);
                }
            }
        }
    }
}
 
void
rb_const_set(VALUE klass, ID id, VALUE val)
{
    const_set(klass, id, val);
    const_added(klass, id);
}
 
static VALUE
autoload_const_value_for_named_constant(VALUE module, ID name, struct autoload_const **autoload_const_pointer)
{
    VALUE autoload_const_value = autoload_entry(module, name);
    if (!autoload_const_value) return Qfalse;
 
    struct autoload_data *autoload_data = get_autoload_data(autoload_const_value, autoload_const_pointer);
    if (!autoload_data) return Qfalse;
 
    /* for autoloading thread, keep the defined value to autoloading storage */
    if (autoload_by_current(autoload_data)) {
        return autoload_const_value;
    }
 
    return Qfalse;
}
 
/* Records into *warning rather than warning itself; see struct const_warning. */
static void
const_tbl_update(struct autoload_const *ac, int autoload_force, struct const_warning *warning)
{
    ASSERT_vm_locking();
    VALUE value;
    VALUE klass = ac->module;
    VALUE val = ac->value;
    ID id = ac->name;
    struct rb_id_table *tbl = RCLASS_CONST_TBL(klass);
    rb_const_flag_t visibility = ac->flag;
    rb_const_entry_t *ce;
 
    if (rb_id_table_lookup(tbl, id, &value)) {
        ce = (rb_const_entry_t *)value;
        if (UNDEF_P(ce->value)) {
            RUBY_ASSERT_CRITICAL_SECTION_ENTER();
            VALUE file = ac->file;
            int line = ac->line;
            VALUE autoload_const_value = autoload_const_value_for_named_constant(klass, id, &ac);
 
            if (!autoload_force && autoload_const_value) {
                rb_clear_constant_cache_for_id(id);
 
                RB_OBJ_WRITE(autoload_const_value, &ac->value, val);
                RB_OBJ_WRITE(autoload_const_value, &ac->file, rb_source_location(&ac->line));
            }
            else {
                /* otherwise autoloaded constant, allow to override */
                autoload_delete(ce->u.autoload_const);
                ce->flag = visibility;
                RB_OBJ_WRITE(klass, &ce->value, val);
                RB_OBJ_WRITE(klass, &ce->u.file, file);
                ce->line = line;
            }
            RUBY_ASSERT_CRITICAL_SECTION_LEAVE();
            return;
        }
        else {
            visibility = ce->flag;
 
            warning->id = id;
            warning->module = klass;
            warning->file = ce->u.file;
            warning->line = ce->line;
        }
        rb_clear_constant_cache_for_id(id);
        setup_const_entry(ce, klass, val, visibility);
    }
    else {
        tbl = RCLASS_WRITABLE_CONST_TBL(klass);
        rb_clear_constant_cache_for_id(id);
 
        ce = ZALLOC(rb_const_entry_t);
        rb_id_table_insert(tbl, id, (VALUE)ce);
        setup_const_entry(ce, klass, val, visibility);
    }
}
 
static void
setup_const_entry(rb_const_entry_t *ce, VALUE klass, VALUE val,
                  rb_const_flag_t visibility)
{
    ce->flag = visibility;
    RB_OBJ_WRITE(klass, &ce->value, val);
    RB_OBJ_WRITE(klass, &ce->u.file, rb_source_location(&ce->line));
}
 
void
rb_define_const(VALUE klass, const char *name, VALUE val)
{
    ID id = rb_intern(name);
 
    if (!rb_is_const_id(id)) {
        rb_warn("rb_define_const: invalid name '%s' for constant", name);
    }
    if (!RB_SPECIAL_CONST_P(val)) {
        rb_vm_register_global_object(val);
    }
    rb_const_set(klass, id, val);
}
 
void
rb_define_global_const(const char *name, VALUE val)
{
    rb_define_const(rb_cObject, name, val);
}
 
static void
set_const_visibility(VALUE mod, int argc, const VALUE *argv,
                     rb_const_flag_t flag, rb_const_flag_t mask)
{
    int i;
    rb_const_entry_t *ce;
    ID id;
 
    rb_class_modify_check(mod);
    if (argc == 0) {
        rb_warning("%"PRIsVALUE" with no argument is just ignored",
                   QUOTE_ID(rb_frame_callee()));
        return;
    }
 
    for (i = 0; i < argc; i++) {
        struct autoload_const *ac;
        VALUE val = argv[i];
        id = rb_check_id(&val);
        if (!id) {
            undefined_constant(mod, val);
        }
        if ((ce = rb_const_lookup(mod, id))) {
            ce->flag &= ~mask;
            ce->flag |= flag;
            if (UNDEF_P(ce->value)) {
                if (autoload_const_value_for_named_constant(mod, id, &ac)) {
                    ac->flag &= ~mask;
                    ac->flag |= flag;
                }
            }
            rb_clear_constant_cache_for_id(id);
        }
        else {
            undefined_constant(mod, ID2SYM(id));
        }
    }
}
 
void
rb_deprecate_constant(VALUE mod, const char *name)
{
    rb_const_entry_t *ce;
    ID id;
    long len = strlen(name);
 
    rb_class_modify_check(mod);
    if (!(id = rb_check_id_cstr(name, len, NULL))) {
        undefined_constant(mod, rb_fstring_new(name, len));
    }
    if (!(ce = rb_const_lookup(mod, id))) {
        undefined_constant(mod, ID2SYM(id));
    }
    ce->flag |= CONST_DEPRECATED;
}
 
/*
 *  call-seq:
 *     mod.private_constant(symbol, ...)    => mod
 *
 *  Makes a list of existing constants private.
 */
 
VALUE
rb_mod_private_constant(int argc, const VALUE *argv, VALUE obj)
{
    set_const_visibility(obj, argc, argv, CONST_PRIVATE, CONST_VISIBILITY_MASK);
    return obj;
}
 
/*
 *  call-seq:
 *     mod.public_constant(symbol, ...)    => mod
 *
 *  Makes a list of existing constants public.
 */
 
VALUE
rb_mod_public_constant(int argc, const VALUE *argv, VALUE obj)
{
    set_const_visibility(obj, argc, argv, CONST_PUBLIC, CONST_VISIBILITY_MASK);
    return obj;
}
 
/*
 *  call-seq:
 *     mod.deprecate_constant(symbol, ...)    => mod
 *
 *  Makes a list of existing constants deprecated. Attempt
 *  to refer to them will produce a warning.
 *
 *     module HTTP
 *       NotFound = Exception.new
 *       NOT_FOUND = NotFound # previous version of the library used this name
 *
 *       deprecate_constant :NOT_FOUND
 *     end
 *
 *     HTTP::NOT_FOUND
 *     # warning: constant HTTP::NOT_FOUND is deprecated
 *
 */
 
VALUE
rb_mod_deprecate_constant(int argc, const VALUE *argv, VALUE obj)
{
    set_const_visibility(obj, argc, argv, CONST_DEPRECATED, CONST_DEPRECATED);
    return obj;
}
 
static VALUE
original_module(VALUE c)
{
    if (RB_TYPE_P(c, T_ICLASS))
        return RBASIC(c)->klass;
    return c;
}
 
static int
cvar_lookup_at(VALUE klass, ID id, st_data_t *v)
{
    if (RB_TYPE_P(klass, T_ICLASS)) {
        if (RICLASS_IS_ORIGIN_P(klass)) {
            return 0;
        }
        else {
            // check the original module
            klass = RBASIC(klass)->klass;
        }
    }
 
    VALUE n = rb_ivar_lookup(klass, id, Qundef);
    if (UNDEF_P(n)) return 0;
 
    if (v) *v = n;
    return 1;
}
 
static VALUE
cvar_front_klass(VALUE klass)
{
    if (RCLASS_SINGLETON_P(klass)) {
        VALUE obj = RCLASS_ATTACHED_OBJECT(klass);
        if (rb_namespace_p(obj)) {
            return obj;
        }
    }
    return RCLASS_SUPER(klass);
}
 
static void
cvar_overtaken_check(VALUE front, VALUE target, ID id)
{
    if (front && target != front && original_module(front) != original_module(target)) {
        rb_raise(rb_eRuntimeError,
                 "class variable % "PRIsVALUE" of %"PRIsVALUE" is overtaken by %"PRIsVALUE"",
                   ID2SYM(id), rb_class_name(original_module(front)),
                   rb_class_name(original_module(target)));
    }
}
 
// the clean-up after cvar_overtaken_check
static void
cvar_overtaken(VALUE front, VALUE target, ID id)
{
    if (front && target != front) {
        if (BUILTIN_TYPE(front) == T_CLASS && rb_class_owned_p(front)) {
            // only clean-up, and reachable from reads: never write a foreign class
            rb_ivar_delete(front, id, Qundef);
        }
    }
}
 
#define CVAR_FOREACH_ANCESTORS(klass, v, r) \
    for (klass = cvar_front_klass(klass); klass; klass = RCLASS_SUPER(klass)) { \
        if (cvar_lookup_at(klass, id, (v))) { \
            r; \
        } \
    }
 
#define CVAR_LOOKUP(v,r) do {\
    if (cvar_lookup_at(klass, id, (v))) {r;}\
    CVAR_FOREACH_ANCESTORS(klass, v, r);\
} while(0)
 
static VALUE
find_cvar(VALUE klass, VALUE * front, VALUE * target, ID id)
{
    VALUE v = Qundef;
    CVAR_LOOKUP(&v, {
        if (!*front) {
            *front = klass;
        }
        *target = klass;
    });
 
    return v;
}
 
void
rb_cvar_set(VALUE klass, ID id, VALUE val)
{
    VALUE tmp, front = 0, target = 0;
 
    tmp = klass;
    CVAR_LOOKUP(0, {if (!front) front = klass; target = klass;});
    if (target) {
        cvar_overtaken_check(front, target, id);
        cvar_overtaken(front, target, id);
    }
    else {
        target = tmp;
    }
 
    if (RB_TYPE_P(target, T_ICLASS)) {
        target = RBASIC(target)->klass;
    }
    cvar_set_ractor_check(target, id);
    check_before_mod_set(target, id, val, "class variable");
 
    bool new_cvar = rb_class_ivar_set(target, id, val);
 
    VALUE cvc_tbl = RCLASS_WRITABLE_CVC_TBL(target);
 
    struct rb_cvar_class_tbl_entry *ent;
    VALUE ent_data;
 
    if (!cvc_tbl || !rb_marked_id_table_lookup(cvc_tbl, id, &ent_data)) {
        ent = (struct rb_cvar_class_tbl_entry *)SHAREABLE_IMEMO_NEW(struct rb_cvar_class_tbl_entry, imemo_cvar_entry, 0);
        RB_OBJ_WRITE((VALUE)ent, &ent->class_value, target);
        RB_OBJ_WRITE((VALUE)ent, &ent->cref, 0);
        ent->global_cvar_state = GET_GLOBAL_CVAR_STATE();
 
        VALUE new_cvc_tbl = cvc_tbl;
        if (!new_cvc_tbl) {
            new_cvc_tbl = rb_marked_id_table_new(2);
        }
        else if (rb_multi_ractor_p()) {
            new_cvc_tbl = rb_marked_id_table_dup(cvc_tbl);
        }
 
        rb_marked_id_table_insert(new_cvc_tbl, id, (VALUE)ent);
        if (new_cvc_tbl != cvc_tbl) {
            RCLASS_WRITE_CVC_TBL(target, new_cvc_tbl);
        }
        RB_DEBUG_COUNTER_INC(cvar_inline_miss);
    }
    else {
        ent = (void *)ent_data;
        ent->global_cvar_state = GET_GLOBAL_CVAR_STATE();
    }
 
    // Break the cvar cache if this is a new class variable.
    // Existing caches may have resolved this name to a different
    // location in the hierarchy, so we must invalidate globally.
    if (new_cvar) {
        ruby_vm_global_cvar_state++;
    }
}
 
VALUE
rb_cvar_find(VALUE klass, ID id, VALUE *front)
{
    VALUE target = 0;
    VALUE value;
 
    value = find_cvar(klass, front, &target, id);
    if (!target) {
        rb_name_err_raise("uninitialized class variable %1$s in %2$s",
                          klass, ID2SYM(id));
    }
    cvar_overtaken_check(*front, target, id);
    // before the clean-up in cvar_overtaken, which may GC: only this stack holds value until the owner has it
    cvar_read_ractor_check(RB_TYPE_P(target, T_ICLASS) ? RBASIC(target)->klass : target, id, value);
    cvar_overtaken(*front, target, id);
    return value;
}
 
VALUE
rb_cvar_get(VALUE klass, ID id)
{
    VALUE front = 0;
    return rb_cvar_find(klass, id, &front);
}
 
VALUE
rb_cvar_defined(VALUE klass, ID id)
{
    if (!klass) return Qfalse;
    CVAR_LOOKUP(0,return Qtrue);
    return Qfalse;
}
 
static ID
cv_intern(VALUE klass, const char *name)
{
    ID id = rb_intern(name);
    if (!rb_is_class_id(id)) {
        rb_name_err_raise("wrong class variable name %1$s",
                          klass, rb_str_new_cstr(name));
    }
    return id;
}
 
void
rb_cv_set(VALUE klass, const char *name, VALUE val)
{
    ID id = cv_intern(klass, name);
    rb_cvar_set(klass, id, val);
}
 
VALUE
rb_cv_get(VALUE klass, const char *name)
{
    ID id = cv_intern(klass, name);
    return rb_cvar_get(klass, id);
}
 
void
rb_define_class_variable(VALUE klass, const char *name, VALUE val)
{
    rb_cv_set(klass, name, val);
}
 
static int
cv_i(ID key, VALUE v, st_data_t a)
{
    st_table *tbl = (st_table *)a;
 
    if (rb_is_class_id(key)) {
        st_update(tbl, (st_data_t)key, cv_i_update, 0);
    }
    return ST_CONTINUE;
}
 
static void*
mod_cvar_at(VALUE mod, void *data)
{
    st_table *tbl = data;
    if (!tbl) {
        tbl = st_init_numtable();
    }
    mod = original_module(mod);
 
    rb_ivar_foreach(mod, cv_i, (st_data_t)tbl);
    return tbl;
}
 
static void*
mod_cvar_of(VALUE mod, void *data)
{
    VALUE tmp = mod;
    if (RCLASS_SINGLETON_P(mod)) {
        if (rb_namespace_p(RCLASS_ATTACHED_OBJECT(mod))) {
            data = mod_cvar_at(tmp, data);
            tmp = cvar_front_klass(tmp);
        }
    }
    for (;;) {
        data = mod_cvar_at(tmp, data);
        tmp = RCLASS_SUPER(tmp);
        if (!tmp) break;
    }
    return data;
}
 
static int
cv_list_i(st_data_t key, st_data_t value, VALUE ary)
{
    ID sym = (ID)key;
    rb_ary_push(ary, ID2SYM(sym));
    return ST_CONTINUE;
}
 
static VALUE
cvar_list(void *data)
{
    st_table *tbl = data;
    VALUE ary;
 
    if (!tbl) return rb_ary_new2(0);
    ary = rb_ary_new2(tbl->num_entries);
    st_foreach_safe(tbl, cv_list_i, ary);
    st_free_table(tbl);
 
    return ary;
}
 
/*
 *  call-seq:
 *     mod.class_variables(inherit=true)    -> array
 *
 *  Returns an array of the names of class variables in <i>mod</i>.
 *  This includes the names of class variables in any included
 *  modules, unless the <i>inherit</i> parameter is set to
 *  <code>false</code>.
 *
 *     class One
 *       @@var1 = 1
 *     end
 *     class Two < One
 *       @@var2 = 2
 *     end
 *     One.class_variables          #=> [:@@var1]
 *     Two.class_variables          #=> [:@@var2, :@@var1]
 *     Two.class_variables(false)   #=> [:@@var2]
 */
 
VALUE
rb_mod_class_variables(int argc, const VALUE *argv, VALUE mod)
{
    bool inherit = true;
    st_table *tbl;
 
    if (rb_check_arity(argc, 0, 1)) inherit = RTEST(argv[0]);
    if (inherit) {
        tbl = mod_cvar_of(mod, 0);
    }
    else {
        tbl = mod_cvar_at(mod, 0);
    }
    return cvar_list(tbl);
}
 
/*
 *  call-seq:
 *     remove_class_variable(sym)    -> obj
 *
 *  Removes the named class variable from the receiver, returning that
 *  variable's value.
 *
 *     class Example
 *       @@var = 99
 *       puts remove_class_variable(:@@var)
 *       p(defined? @@var)
 *     end
 *
 *  <em>produces:</em>
 *
 *     99
 *     nil
 */
 
VALUE
rb_mod_remove_cvar(VALUE mod, VALUE name)
{
    const ID id = id_for_var_message(mod, name, class, "wrong class variable name %1$s");
    st_data_t val;
 
    if (!id) {
        goto not_defined;
    }
    rb_check_frozen(mod);
    cvar_set_ractor_check(mod, id);
    val = rb_ivar_delete(mod, id, Qundef);
    if (!UNDEF_P(val)) {
        return (VALUE)val;
    }
    if (rb_cvar_defined(mod, id)) {
        rb_name_err_raise("cannot remove %1$s for %2$s", mod, ID2SYM(id));
    }
  not_defined:
    rb_name_err_raise("class variable %1$s not defined for %2$s",
                      mod, name);
    UNREACHABLE_RETURN(Qundef);
}
 
VALUE
rb_iv_get(VALUE obj, const char *name)
{
    ID id = rb_check_id_cstr(name, strlen(name), rb_usascii_encoding());
 
    if (!id) {
        return Qnil;
    }
    return rb_ivar_get(obj, id);
}
 
VALUE
rb_iv_set(VALUE obj, const char *name, VALUE val)
{
    ID id = rb_intern(name);
 
    return rb_ivar_set(obj, id, val);
}
 
static attr_index_t
class_fields_ivar_set(VALUE klass, VALUE fields_obj, ID id, VALUE val, bool concurrent, VALUE *new_fields_obj, bool *new_ivar_out)
{
    const VALUE original_fields_obj = fields_obj;
    fields_obj = original_fields_obj ? original_fields_obj : rb_imemo_fields_new(klass, ROOT_SHAPE_ID, true);
 
    shape_id_t current_shape_id = RBASIC_SHAPE_ID(fields_obj);
    shape_id_t next_shape_id = current_shape_id; // for complex
    if (UNLIKELY(rb_shape_complex_p(current_shape_id))) {
        goto complex;
    }
 
    bool new_ivar;
    next_shape_id = generic_shape_ivar(fields_obj, id, &new_ivar);
 
    if (UNLIKELY(rb_shape_complex_p(next_shape_id))) {
        fields_obj = imemo_fields_evacutate_to_complex(klass, fields_obj, next_shape_id, 1);
        goto complex;
    }
 
    attr_index_t index = RSHAPE_INDEX(next_shape_id);
    if (new_ivar && index >= RSHAPE_CAPACITY(current_shape_id)) {
        // We allocate a new fields_obj even when concurrency isn't a concern
        // so that we're embedded as long as possible.
        fields_obj = imemo_fields_copy_append(klass, fields_obj, current_shape_id, next_shape_id, val);
    }
    else {
        VALUE *fields = rb_imemo_fields_ptr(fields_obj);
 
        if (concurrent && original_fields_obj == fields_obj) {
            // In the concurrent case, if we're mutating the existing
            // fields_obj, we must use an atomic write, because if we're
            // adding a new field, the shape_id must be written after the field
            // and if we're updating an existing field, we at least need a relaxed
            // write to avoid reaping.
            RB_OBJ_ATOMIC_WRITE(fields_obj, &fields[index], val);
        }
        else {
            RB_OBJ_WRITE(fields_obj, &fields[index], val);
        }
 
        if (new_ivar) {
            RUBY_ASSERT(rb_shape_layout(next_shape_id) == SHAPE_ID_LAYOUT_ROBJECT);
            RBASIC_SET_SHAPE_ID(fields_obj, next_shape_id);
        }
    }
 
    *new_fields_obj = fields_obj;
    *new_ivar_out = new_ivar;
    return index;
 
complex:
    {
        if (concurrent && fields_obj == original_fields_obj) {
            // In multi-ractor case, we must always work on a copy because
            // even if the field already exist, inserting in a st_table may
            // cause a rebuild.
            fields_obj = rb_imemo_fields_clone(fields_obj);
        }
 
        st_table *table = rb_imemo_fields_complex_tbl(fields_obj);
        new_ivar = !st_insert(table, (st_data_t)id, (st_data_t)val);
        RB_OBJ_WRITTEN(fields_obj, Qundef, val);
 
        if (fields_obj != original_fields_obj) {
            RUBY_ASSERT(rb_shape_layout(next_shape_id) == SHAPE_ID_LAYOUT_ROBJECT);
            RBASIC_SET_SHAPE_ID(fields_obj, next_shape_id);
        }
    }
 
    *new_fields_obj = fields_obj;
    *new_ivar_out = new_ivar;
    return ATTR_INDEX_NOT_SET;
}
 
static attr_index_t
class_ivar_set(VALUE obj, ID id, VALUE val, bool *new_ivar)
{
    rb_class_ensure_writable(obj);
 
    const VALUE original_fields_obj = RCLASS_WRITABLE_FIELDS_OBJ(obj);
    VALUE new_fields_obj = 0;
 
    attr_index_t index = class_fields_ivar_set(obj, original_fields_obj, id, val, rb_multi_ractor_p(), &new_fields_obj, new_ivar);
 
    if (new_fields_obj != original_fields_obj) {
        RCLASS_WRITABLE_SET_FIELDS_OBJ(obj, new_fields_obj);
    }
 
    // TODO: What should we set as the T_CLASS shape_id?
    // In most case we can replicate the single `fields_obj` shape
    // but in namespaced case? Perhaps INVALID_SHAPE_ID?
    RBASIC_SET_SHAPE_ID(obj, RBASIC_SHAPE_ID(new_fields_obj));
    return index;
}
 
bool
rb_class_ivar_set(VALUE obj, ID id, VALUE val)
{
    RUBY_ASSERT(RB_TYPE_P(obj, T_CLASS) || RB_TYPE_P(obj, T_MODULE));
    rb_check_frozen(obj);
 
    bool new_ivar;
    class_ivar_set(obj, id, val, &new_ivar);
    return new_ivar;
}
 
void
rb_fields_tbl_copy(VALUE dst, VALUE src)
{
    RUBY_ASSERT(rb_type(dst) == rb_type(src));
    RUBY_ASSERT(RB_TYPE_P(dst, T_CLASS) || RB_TYPE_P(dst, T_MODULE));
    RUBY_ASSERT(RSHAPE_TYPE_P(RBASIC_SHAPE_ID(dst), SHAPE_ROOT));
 
    VALUE fields_obj = RCLASS_WRITABLE_FIELDS_OBJ(src);
    if (fields_obj) {
        VALUE dst_fields_obj = rb_imemo_fields_clone(fields_obj);
        // `dst` is a freshly allocated object, so it must not inherit `src`'s
        // frozen status. Callers that need it re-freeze `dst` themselves.
        shape_id_t shape_id = RBASIC_SHAPE_ID(dst_fields_obj) & ~SHAPE_ID_FL_FROZEN;
        RBASIC_SET_SHAPE_ID(dst_fields_obj, shape_id);
        RCLASS_WRITABLE_SET_FIELDS_OBJ(dst, dst_fields_obj);
        RBASIC_SET_SHAPE_ID(dst, shape_id);
    }
}
 
static rb_const_entry_t *
const_lookup(struct rb_id_table *tbl, ID id)
{
    if (tbl) {
        VALUE val;
        bool r;
        RB_VM_LOCKING() {
            r = rb_id_table_lookup(tbl, id, &val);
        }
 
        if (r) return (rb_const_entry_t *)val;
    }
    return NULL;
}
 
rb_const_entry_t *
rb_const_lookup(VALUE klass, ID id)
{
    return const_lookup(RCLASS_CONST_TBL(klass), id);
}
 
// For readers that may not own klass: rb_const_remove frees the entry once it is out of
// the table, so copy it while the VM lock keeps it in.
bool
rb_const_lookup_copy(VALUE klass, ID id, rb_const_entry_t *ce)
{
    bool found = false;
    RB_VM_LOCKING() {
        struct rb_id_table *tbl = RCLASS_CONST_TBL(klass);
        VALUE entry;
        if (tbl && rb_id_table_lookup(tbl, id, &entry)) {
            *ce = *(rb_const_entry_t *)entry;
            found = true;
        }
    }
    return found;
}