class TracePoint

A class that provides the functionality of Kernel#set_trace_func in a nice Object-Oriented API.

Example¶ ↑

We can use TracePoint to gather information specifically for exceptions:

trace = TracePoint.new(:raise) do |tp|
    p [tp.lineno, tp.event, tp.raised_exception]
end
#=> #<TracePoint:disabled>

trace.enable
#=> false

0 / 0
#=> [5, :raise, #<ZeroDivisionError: divided by 0>]

Events¶ ↑

If you don't specify the type of events you want to listen for, TracePoint will include all available events.

Note do not depend on current event set, as this list is subject to change. Instead, it is recommended you specify the type of events you want to use.

To filter what is traced, you can pass any of the following as events:

:line: execute code on a new line
:class: start a class or module definition
:end: finish a class or module definition
:call: call a Ruby method
:return: return from a Ruby method
:c_call: call a C-language routine
:c_return: return from a C-language routine
:raise: raise an exception
:b_call: event hook at block entry
:b_return: event hook at block ending
:thread_begin: event hook at thread beginning
:thread_end: event hook at thread ending

Public Class Methods

new(*events) { |obj| block } → obj click to toggle source

Returns a new TracePoint object, not enabled by default.

Next, in order to activate the trace, you must use #enable

trace = TracePoint.new(:call) do |tp|
    p [tp.lineno, tp.defined_class, tp.method_id, tp.event]
end
#=> #<TracePoint:disabled>

trace.enable
#=> false

puts "Hello, TracePoint!"
# ...
# [48, IRB::Notifier::AbstractNotifier, :printf, :call]
# ...

When you want to deactivate the trace, you must use #disable

trace.disable

See Events at TracePoint for possible events and more information.

A block must be given, otherwise a ThreadError is raised.

If the trace method isn't included in the given events filter, a RuntimeError is raised.

TracePoint.trace(:line) do |tp|
    p tp.raised_exception
end
#=> RuntimeError: 'raised_exception' not supported by this event

If the trace method is called outside block, a RuntimeError is raised.

TracePoint.trace(:line) do |tp|
  $tp = tp
end
$tp.line #=> access from outside (RuntimeError)

Access from other threads is also forbidden.

static VALUE
tracepoint_new_s(int argc, VALUE *argv, VALUE self)
{
    rb_event_flag_t events = 0;
    int i;

    if (argc > 0) {
        for (i=0; i<argc; i++) {
            events |= symbol2event_flag(argv[i]);
        }
    }
    else {
        events = RUBY_EVENT_TRACEPOINT_ALL;
    }

    if (!rb_block_given_p()) {
        rb_raise(rb_eThreadError, "must be called with a block");
    }

    return tracepoint_new(self, 0, events, 0, 0, rb_block_proc());
}

trace(*events) { |obj| block } → obj click to toggle source

A convenience method for ::new, that activates the trace automatically.

trace = TracePoint.trace(:call) { |tp| [tp.lineno, tp.event] }
#=> #<TracePoint:enabled>

trace.enabled? #=> true

static VALUE
tracepoint_trace_s(int argc, VALUE *argv, VALUE self)
{
    VALUE trace = tracepoint_new_s(argc, argv, self);
    rb_tracepoint_enable(trace);
    return trace;
}

Public Instance Methods

binding() click to toggle source

Return the generated binding object from event

static VALUE
tracepoint_attr_binding(VALUE tpval)
{
    return rb_tracearg_binding(get_trace_arg());
}

defined_class() click to toggle source

Return class or module of the method being called.

class C; def foo; end; end
trace = TracePoint.new(:call) do |tp|
  p tp.defined_class #=> C
end.enable do
  C.new.foo
end

If method is defined by a module, then that module is returned.

module M; def foo; end; end
class C; include M; end;
trace = TracePoint.new(:call) do |tp|
  p tp.defined_class #=> M
end.enable do
  C.new.foo
end

Note: defined_class returns singleton class.

6th block parameter of Kernel#set_trace_func passes original class of attached by singleton class.

This is a difference between Kernel#set_trace_func and TracePoint.

class C; def self.foo; end; end
trace = TracePoint.new(:call) do |tp|
  p tp.defined_class #=> #<Class:C>
end.enable do
  C.foo
end

static VALUE
tracepoint_attr_defined_class(VALUE tpval)
{
    return rb_tracearg_defined_class(get_trace_arg());
}

disable → true or false click to toggle source

disable { block } → obj

Deactivates the trace

Return true if trace was enabled. Return false if trace was disabled.

trace.enabled?       #=> true
trace.disable        #=> false (previous status)
trace.enabled?       #=> false
trace.disable        #=> false

If a block is given, the trace will only be disable within the scope of the block.

trace.enabled?
#=> true

trace.disable do
    trace.enabled?
    # only disabled for this block
end

trace.enabled?
#=> true

Note: You cannot access event hooks within the block.

trace.disable { p tp.lineno }
#=> RuntimeError: access from outside

static VALUE
tracepoint_disable_m(VALUE tpval)
{
    rb_tp_t *tp = tpptr(tpval);
    int previous_tracing = tp->tracing;
    rb_tracepoint_disable(tpval);

    if (rb_block_given_p()) {
        return rb_ensure(rb_yield, Qnil,
                         previous_tracing ? rb_tracepoint_enable : rb_tracepoint_disable,
                         tpval);
    }
    else {
        return previous_tracing ? Qtrue : Qfalse;
    }
}

enable → true or false click to toggle source

enable { block } → obj

Activates the trace

Return true if trace was enabled. Return false if trace was disabled.

trace.enabled?  #=> false
trace.enable    #=> false (previous state)
                #   trace is enabled
trace.enabled?  #=> true
trace.enable    #=> true (previous state)
                #   trace is still enabled

If a block is given, the trace will only be enabled within the scope of the block.

trace.enabled?
#=> false

trace.enable do
    trace.enabled?
    # only enabled for this block
end

trace.enabled?
#=> false

Note: You cannot access event hooks within the block.

trace.enable { p tp.lineno }
#=> RuntimeError: access from outside

static VALUE
tracepoint_enable_m(VALUE tpval)
{
    rb_tp_t *tp = tpptr(tpval);
    int previous_tracing = tp->tracing;
    rb_tracepoint_enable(tpval);

    if (rb_block_given_p()) {
        return rb_ensure(rb_yield, Qnil,
                         previous_tracing ? rb_tracepoint_enable : rb_tracepoint_disable,
                         tpval);
    }
    else {
        return previous_tracing ? Qtrue : Qfalse;
    }
}

enabled? → true or false click to toggle source

The current status of the trace

VALUE
rb_tracepoint_enabled_p(VALUE tpval)
{
    rb_tp_t *tp = tpptr(tpval);
    return tp->tracing ? Qtrue : Qfalse;
}

event() click to toggle source

Type of event

See Events at TracePoint for more information.

static VALUE
tracepoint_attr_event(VALUE tpval)
{
    return rb_tracearg_event(get_trace_arg());
}

inspect → string click to toggle source

Return a string containing a human-readable TracePoint status.

static VALUE
tracepoint_inspect(VALUE self)
{
    rb_tp_t *tp = tpptr(self);
    rb_trace_arg_t *trace_arg = GET_THREAD()->trace_arg;

    if (trace_arg) {
        switch (trace_arg->event) {
          case RUBY_EVENT_LINE:
          case RUBY_EVENT_SPECIFIED_LINE:
            {
                VALUE sym = rb_tracearg_method_id(trace_arg);
                if (NIL_P(sym))
                  goto default_inspect;
                return rb_sprintf("#<TracePoint:%"PRIsVALUE"@%"PRIsVALUE":%d in `%"PRIsVALUE"'>",
                                  rb_tracearg_event(trace_arg),
                                  rb_tracearg_path(trace_arg),
                                  FIX2INT(rb_tracearg_lineno(trace_arg)),
                                  sym);
            }
          case RUBY_EVENT_CALL:
          case RUBY_EVENT_C_CALL:
          case RUBY_EVENT_RETURN:
          case RUBY_EVENT_C_RETURN:
            return rb_sprintf("#<TracePoint:%"PRIsVALUE" `%"PRIsVALUE"'@%"PRIsVALUE":%d>",
                              rb_tracearg_event(trace_arg),
                              rb_tracearg_method_id(trace_arg),
                              rb_tracearg_path(trace_arg),
                              FIX2INT(rb_tracearg_lineno(trace_arg)));
          case RUBY_EVENT_THREAD_BEGIN:
          case RUBY_EVENT_THREAD_END:
            return rb_sprintf("#<TracePoint:%"PRIsVALUE" %"PRIsVALUE">",
                              rb_tracearg_event(trace_arg),
                              rb_tracearg_self(trace_arg));
          default:
          default_inspect:
            return rb_sprintf("#<TracePoint:%"PRIsVALUE"@%"PRIsVALUE":%d>",
                              rb_tracearg_event(trace_arg),
                              rb_tracearg_path(trace_arg),
                              FIX2INT(rb_tracearg_lineno(trace_arg)));
        }
    }
    else {
        return rb_sprintf("#<TracePoint:%s>", tp->tracing ? "enabled" : "disabled");
    }
}

lineno() click to toggle source

Line number of the event

static VALUE
tracepoint_attr_lineno(VALUE tpval)
{
    return rb_tracearg_lineno(get_trace_arg());
}

method_id() click to toggle source

Return the name of the method being called

static VALUE
tracepoint_attr_method_id(VALUE tpval)
{
    return rb_tracearg_method_id(get_trace_arg());
}

path() click to toggle source

Path of the file being run

static VALUE
tracepoint_attr_path(VALUE tpval)
{
    return rb_tracearg_path(get_trace_arg());
}

raised_exception() click to toggle source

Value from exception raised on the :raise event

static VALUE
tracepoint_attr_raised_exception(VALUE tpval)
{
    return rb_tracearg_raised_exception(get_trace_arg());
}

return_value() click to toggle source

Return value from :return, c_return, and b_return event

static VALUE
tracepoint_attr_return_value(VALUE tpval)
{
    return rb_tracearg_return_value(get_trace_arg());
}

self() click to toggle source

Return the trace object during event

Same as #binding:

trace.binding.eval('self')

static VALUE
tracepoint_attr_self(VALUE tpval)
{
    return rb_tracearg_self(get_trace_arg());
}