memory.h File Reference

(892c46283a5ea4179500d951c9d4866c0051f27b)

Memory management stuff. More...

#include "ruby/internal/config.h"
#include "ruby/internal/attr/alloc_size.h"
#include "ruby/internal/attr/const.h"
#include "ruby/internal/attr/constexpr.h"
#include "ruby/internal/attr/noalias.h"
#include "ruby/internal/attr/nonnull.h"
#include "ruby/internal/attr/noreturn.h"
#include "ruby/internal/attr/restrict.h"
#include "ruby/internal/attr/returns_nonnull.h"
#include "ruby/internal/cast.h"
#include "ruby/internal/dllexport.h"
#include "ruby/internal/has/builtin.h"
#include "ruby/internal/stdalign.h"
#include "ruby/internal/stdbool.h"
#include "ruby/internal/stdckdint.h"
#include "ruby/internal/xmalloc.h"
#include "ruby/backward/2/limits.h"
#include "ruby/backward/2/long_long.h"
#include "ruby/backward/2/assume.h"
#include "ruby/defines.h"

Include dependency graph for memory.h:

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Macros
#define	RUBY_ALLOCV_LIMIT   1024
	Maximum possible number of bytes that RB_ALLOCV can allocate using alloca. More...
#define	RB_GC_GUARD(v)
	Prevents premature destruction of local objects. More...
#define	RB_ALLOC_N(type, n)   RBIMPL_CAST((type *)ruby_xmalloc2((n), sizeof(type)))
	Convenient macro that allocates an array of n elements. More...
#define	RB_ALLOC(type)   RBIMPL_CAST((type *)ruby_xmalloc(sizeof(type)))
	Shorthand of RB_ALLOC_N with n=1. More...
#define	RB_ZALLOC_N(type, n)   RBIMPL_CAST((type *)ruby_xcalloc((n), sizeof(type)))
	Identical to RB_ALLOC_N() but also nullifies the allocated region before returning. More...
#define	RB_ZALLOC(type)   (RB_ZALLOC_N(type, 1))
	Shorthand of RB_ZALLOC_N with n=1. More...
#define	RB_REALLOC_N(var, type, n)    ((var) = RBIMPL_CAST((type *)ruby_xrealloc2((void *)(var), (n), sizeof(type))))
	Convenient macro that reallocates an array with a new size. More...
#define	ALLOCA_N(type, n)    RBIMPL_CAST((type *)alloca(rbimpl_size_mul_or_raise(sizeof(type), (n))))
#define	RB_ALLOCV(v, n)
	Identical to RB_ALLOCV_N(), except that it allocates a number of bytes and returns a void* . More...
#define	RB_ALLOCV_N(type, v, n)
	Allocates a memory region, possibly on stack. More...
#define	RB_ALLOCV_END(v)   rb_free_tmp_buffer(&(v))
	Polite way to declare that the given array is not used any longer. More...
#define	MEMZERO(p, type, n)   memset((p), 0, rbimpl_size_mul_or_raise(sizeof(type), (n)))
	Handy macro to erase a region of memory. More...
#define	MEMCPY(p1, p2, type, n)   ruby_nonempty_memcpy((p1), (p2), rbimpl_size_mul_or_raise(sizeof(type), (n)))
	Handy macro to call memcpy. More...
#define	MEMMOVE(p1, p2, type, n)   memmove((p1), (p2), rbimpl_size_mul_or_raise(sizeof(type), (n)))
	Handy macro to call memmove. More...
#define	MEMCMP(p1, p2, type, n)   memcmp((p1), (p2), rbimpl_size_mul_or_raise(sizeof(type), (n)))
	Handy macro to call memcmp. More...
#define	ALLOC_N   RB_ALLOC_N
	Old name of RB_ALLOC_N. More...
#define	ALLOC   RB_ALLOC
	Old name of RB_ALLOC. More...
#define	ZALLOC_N   RB_ZALLOC_N
	Old name of RB_ZALLOC_N. More...
#define	ZALLOC   RB_ZALLOC
	Old name of RB_ZALLOC. More...
#define	REALLOC_N   RB_REALLOC_N
	Old name of RB_REALLOC_N. More...
#define	ALLOCV   RB_ALLOCV
	Old name of RB_ALLOCV. More...
#define	ALLOCV_N   RB_ALLOCV_N
	Old name of RB_ALLOCV_N. More...
#define	ALLOCV_END   RB_ALLOCV_END
	Old name of RB_ALLOCV_END. More...

Functions
static int	rb_mul_size_overflow (size_t a, size_t b, size_t max, size_t *c)
static void *	rb_alloc_tmp_buffer2 (volatile VALUE *store, long count, size_t elsize)
	This is an implementation detail of RB_ALLOCV_N(). More...
static void *	ruby_nonempty_memcpy (void *dest, const void *src, size_t n)

Detailed Description

Memory management stuff.

Author

Ruby developers ruby-.nosp@m.core.nosp@m.@ruby.nosp@m.-lan.nosp@m.g.org

Copyright

This file is a part of the programming language Ruby. Permission is hereby granted, to either redistribute and/or modify this file, provided that the conditions mentioned in the file COPYING are met. Consult the file for details.

Warning

Symbols prefixed with either RBIMPL or rbimpl are implementation details. Don't take them as canon. They could rapidly appear then vanish. The name (path) of this header file is also an implementation detail. Do not expect it to persist at the place it is now. Developers are free to move it anywhere anytime at will.

Note

To ruby-core: remember that this header can be possibly recursively included from extension libraries written in C++. Do not expect for instance __VA_ARGS__ is always available. We assume C99 for ruby itself but we don't assume languages of extension libraries. They could be written in C++98.

Definition in file memory.h.

Macro Definition Documentation

ALLOCA_N

#define ALLOCA_N	(		type,
			n
	)		RBIMPL_CAST((type *)alloca(rbimpl_size_mul_or_raise(sizeof(type), (n))))

Deprecated:

This macro is dangerous (does not bother stack overflow at all).

RB_ALLOCV is the modern way to do the same thing.

Parameters

type	Type of array elements.
n	Length of the array.

Returns

A pointer on stack.

Definition at line 287 of file memory.h.

MEMCMP

#define MEMCMP	(		p1,
			p2,
			type,
			n
	)		memcmp((p1), (p2), rbimpl_size_mul_or_raise(sizeof(type), (n)))

Handy macro to call memcmp.

Parameters

p1	Target LHS.
p2	Target RHS.
type	Type of p1[0]
n	Length of p1.

Return values

<0	`p1` is "less" than `p2`.
0	`p1` is equal to `p2`.
>0	p1 is "greater" than p2.

Definition at line 392 of file memory.h.

MEMCPY

#define MEMCPY	(		p1,
			p2,
			type,
			n
	)		ruby_nonempty_memcpy((p1), (p2), rbimpl_size_mul_or_raise(sizeof(type), (n)))

Handy macro to call memcpy.

Parameters

p1	Destination pointer.
p2	Source pointer.
type	Type of p2[0]
n	Length of p2.

Returns

p1.

Postcondition

First n elements of p2 are copied into p1.

Definition at line 367 of file memory.h.

MEMMOVE

#define MEMMOVE	(		p1,
			p2,
			type,
			n
	)		memmove((p1), (p2), rbimpl_size_mul_or_raise(sizeof(type), (n)))

Handy macro to call memmove.

Parameters

p1	Destination pointer.
p2	Source pointer.
type	Type of p2[0]
n	Length of p2.

Returns

p1.

Postcondition

First n elements of p2 are copied into p1.

Definition at line 379 of file memory.h.

MEMZERO

#define MEMZERO	(		p,
			type,
			n
	)		memset((p), 0, rbimpl_size_mul_or_raise(sizeof(type), (n)))

Handy macro to erase a region of memory.

Parameters

p	Target pointer.
type	Type of p[0]
n	Length of p.

Returns

p.

Postcondition

First n elements of p are squashed.

Definition at line 355 of file memory.h.

RB_ALLOC

#define RB_ALLOC

(

type

)

RBIMPL_CAST((type *)ruby_xmalloc(sizeof(type)))

Shorthand of RB_ALLOC_N with n=1.

Parameters

type	Type of allocation.

Exceptions

rb_eNoMemError

No space left for allocation.

Returns

Storage instance that can hold an type object.

Note

It doesn't return NULL.

Warning

The return value shall be invalidated exactly once by either ruby_xfree(), ruby_xrealloc(), or ruby_xrealloc2(). It is a failure to pass it to system free(), because the system and Ruby might or might not share the same malloc() implementation.

Definition at line 208 of file memory.h.

RB_ALLOC_N

#define RB_ALLOC_N	(		type,
			n
	)		RBIMPL_CAST((type *)ruby_xmalloc2((n), sizeof(type)))

Convenient macro that allocates an array of n elements.

Parameters

type	Type of array elements.
n	Length of the array.

Exceptions

rb_eNoMemError	No space left for allocation.
rb_eArgError	Integer overflow trying to calculate the length of continuous memory region of n elements of type.

Returns

Storage instance that is capable of storing at least n elements of type type.

Note

It doesn't return NULL, even when n is zero.

Warning

The return value shall be invalidated exactly once by either ruby_xfree(), ruby_xrealloc(), or ruby_xrealloc2(). It is a failure to pass it to system free(), because the system and Ruby might or might not share the same malloc() implementation.

Definition at line 194 of file memory.h.

RB_ALLOCV

#define RB_ALLOCV	(		v,
			n
	)

Value:

    ((n) < RUBY_ALLOCV_LIMIT ? \
     ((v) = 0, alloca(n)) :    \
     rb_alloc_tmp_buffer(&(v), (n)))

Identical to RB_ALLOCV_N(), except that it allocates a number of bytes and returns a void* .

Parameters

v	A variable to hold the just-in-case opaque Ruby object.
n	Size of allocation, in bytes.

Returns

A void pointer to n bytes storage.

Note

n may be evaluated twice.

Definition at line 299 of file memory.h.

RB_ALLOCV_END

#define RB_ALLOCV_END

(

v

)

rb_free_tmp_buffer(&(v))

Polite way to declare that the given array is not used any longer.

Calling this not mandatory. Our GC can baby-sit you. However it is not a very bad idea to use it when possible. Doing so could reduce memory footprint.

Parameters

v	A variable previously passed to either RB_ALLOCV/RB_ALLOCV_N.

Definition at line 344 of file memory.h.

RB_ALLOCV_N

#define RB_ALLOCV_N	(		type,
			v,
			n
	)

Value:

    RBIMPL_CAST((type *)                                     \
        (((size_t)(n) < RUBY_ALLOCV_LIMIT / sizeof(type)) ? \
         ((v) = 0, alloca((n) * sizeof(type))) :            \
         rb_alloc_tmp_buffer2(&(v), (n), sizeof(type))))

Allocates a memory region, possibly on stack.

If the given size exceeds RUBY_ALLOCV_LIMIT, it allocates a dedicated opaque ruby object instead and let our GC sweep that region after use. Either way you can fire-and-forget.

#include <sys/types.h>
 
VALUE
foo(int n)
{
    VALUE v;
    auto ptr = RB_ALLOCV(struct tms, v, n);
    ...
    // no need to free `ptr`.
}

If you want to be super-duper polite you can also explicitly state the end of use of such memory region by calling RB_ALLOCV_END().

Parameters

type	The type of array elements.
v	A variable to hold the just-in-case opaque Ruby object.
n	Number of elements requested to allocate.

Returns

An array of n elements of type.

Note

n may be evaluated twice.

Definition at line 331 of file memory.h.

RB_GC_GUARD

#define RB_GC_GUARD

(

v

)

Value:

    (*__extension__ ({ \
        volatile VALUE *rb_gc_guarded_ptr = &(v); \
        __asm__("" : : "m"(rb_gc_guarded_ptr)); \
        rb_gc_guarded_ptr; \
    }))

Prevents premature destruction of local objects.

Ruby's garbage collector is conservative; it scans the C level machine stack as well. Possible in- use Ruby objects must remain visible on stack, to be properly marked as such. However contemporary C compilers do not interface well with this. Consider the following example:

auto s = rb_str_new_cstr(" world");
auto sptr = RSTRING_PTR(s);
auto t = rb_str_new_cstr("hello,"); // Possible GC invocation
auto u = rb_str_cat_cstr(t, sptr);
 
RB_GC_GUARD(s); // ensure `s` (and thus `sptr`) do not get GC-ed

Here, without the RB_GC_GUARD, the last use of s is before the last use of sptr. Compilers could thus think s and t are allowed to overlap. That would eliminate s from the stack, while sptr is still in use. If our GC ran at that very moment, s gets swept out, which also destroys sptr. Boom! You got a SEGV.

In order to prevent this scenario RB_GC_GUARD must be placed after the last use of sptr. Placing RB_GC_GUARD before dereferencing sptr would be of no use.

RB_GC_GUARD would not be necessary at all in the above example if non- inlined function calls are made on the s variable after sptr is dereferenced. Thus, in the above example, calling any un-inlined function on s such as rb_str_modify(s); will ensure s stays on the stack or register to prevent a GC invocation from prematurely freeing it.

Using the RB_GC_GUARD macro is preferable to using the volatile keyword in C. RB_GC_GUARD has the following advantages:

• the intent of the macro use is clear.
• RB_GC_GUARD only affects its call site. OTOH volatile generates some extra code every time the variable is used, hurting optimisation.
• volatile implementations may be buggy/inconsistent in some compilers and architectures. RB_GC_GUARD is customisable for broken systems/compilers without negatively affecting other systems.
• C++ since C++20 deprecates volatile. If you write your extension library in that language there is no escape but to use this macro.

Parameters

v	A variable of VALUE type.

Postcondition

v is still alive.

Definition at line 162 of file memory.h.

RB_REALLOC_N

#define RB_REALLOC_N	(		var,
			type,
			n
	)		((var) = RBIMPL_CAST((type *)ruby_xrealloc2((void *)(var), (n), sizeof(type))))

Convenient macro that reallocates an array with a new size.

Parameters

var	A variable of type, which points to a storage instance that was previously returned from either ruby_xmalloc(), ruby_xmalloc2(), ruby_xcalloc(), ruby_xrealloc(), or ruby_xrealloc2().
type	Type of allocation.
n	Requested new size of each element.

Exceptions

rb_eNoMemError	No space left for allocation.
rb_eArgError	Integer overflow trying to calculate the length of continuous memory region of n elements of type.

Returns

Storage instance that is capable of storing at least n elements of type type.

Precondition

The passed variable must point to a valid live storage instance. It is a failure to pass a variable that holds an already-freed pointer.

Note

It doesn't return NULL, even when n is zero.

Warning

Do not assume anything on the alignment of the return value. There is no guarantee that it inherits the passed argument's one.

The return value shall be invalidated exactly once by either ruby_xfree(), ruby_xrealloc(), or ruby_xrealloc2(). It is a failure to pass it to system free(), because the system and Ruby might or might not share the same malloc() implementation.

Definition at line 277 of file memory.h.

RB_ZALLOC

#define RB_ZALLOC

(

type

)

(RB_ZALLOC_N(type, 1))

Shorthand of RB_ZALLOC_N with n=1.

Parameters

type	Type of allocation.

Exceptions

rb_eNoMemError

No space left for allocation.

Returns

Storage instance that can hold an type object.

Postcondition

Returned object is filled with zeros.

Note

It doesn't return NULL.

Warning

The return value shall be invalidated exactly once by either ruby_xfree(), ruby_xrealloc(), or ruby_xrealloc2(). It is a failure to pass it to system free(), because the system and Ruby might or might not share the same malloc() implementation.

Definition at line 244 of file memory.h.

RB_ZALLOC_N

#define RB_ZALLOC_N	(		type,
			n
	)		RBIMPL_CAST((type *)ruby_xcalloc((n), sizeof(type)))

Identical to RB_ALLOC_N() but also nullifies the allocated region before returning.

Parameters

type	Type of array elements.
n	Length of the array.

Exceptions

rb_eNoMemError	No space left for allocation.
rb_eArgError	Integer overflow trying to calculate the length of continuous memory region of n elements of type.

Returns

Storage instance that is capable of storing at least n elements of type type.

Postcondition

Returned array is filled with zeros.

Note

It doesn't return NULL, even when n is zero.

Warning

The return value shall be invalidated exactly once by either ruby_xfree(), ruby_xrealloc(), or ruby_xrealloc2(). It is a failure to pass it to system free(), because the system and Ruby might or might not share the same malloc() implementation.

Definition at line 229 of file memory.h.

RUBY_ALLOCV_LIMIT

#define RUBY_ALLOCV_LIMIT   1024

Maximum possible number of bytes that RB_ALLOCV can allocate using alloca.

Anything beyond this is allocated using rb_alloc_tmp_buffer(). This selection is transparent to users. People don't have to bother.

Definition at line 108 of file memory.h.

Function Documentation

rb_alloc_tmp_buffer2()

static void* rb_alloc_tmp_buffer2 ( volatile VALUE *  store, long  count, size_t  elsize  )

inlinestatic

This is an implementation detail of RB_ALLOCV_N().

People don't use this directly.

Parameters

[out]	store	Pointer to a variable.
[in]	count	Number of elements in an array.
[in]	elsize	Size of each elements.

Returns

Region of count * elsize bytes.

Postcondition

store holds the corresponding tmp buffer object.

Definition at line 644 of file memory.h.

rb_mul_size_overflow()

static int rb_mul_size_overflow ( size_t  a, size_t  b, size_t  max, size_t *  c  )

inlinestatic

Deprecated:

This function was an implementation detail of old RB_ALLOCV_N().

We no longer use it. @shyouhei suspects that there are no actual usage now. However it was not marked as private before. We cannot delete it any longer.

Parameters

[in]	a	Arbitrary value.
[in]	b	Arbitrary value.
[in]	max	Possible maximum value.
[out]	c	A pointer to return the computation result.

Return values

1	c is insane.
0	c is sane.

Postcondition

c holds a * b, but could be overflowed.

Definition at line 526 of file memory.h.