TracePoint

Class

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
:fiber_switch: event hook at fiber switch

Class Methods

TracePoint.new(*events) { |obj| block } → obj

vm_trace.c View on GitHub

          
            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());
}

Returns a new TracePoint object, not enabled by default.

Next, in order to activate the trace, you must use TracePoint.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 TracePoint.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.

TracePoint.stat → obj

vm_trace.c View on GitHub

          
            static VALUE
tracepoint_stat_s(VALUE self)
{
    rb_vm_t *vm = GET_VM();
    VALUE stat = rb_hash_new();

    tracepoint_stat_event_hooks(stat, vm->self, vm->event_hooks.hooks);
    /* TODO: thread local hooks */

    return stat;
}

Returns internal information of TracePoint.

The contents of the returned value are implementation specific. It may be changed in future.

This method is only for debugging TracePoint itself.

TracePoint.trace(*events) { |obj| block } → obj

vm_trace.c View on GitHub

          
            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;
}

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

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

trace.enabled? #=> true

Instance Methods

binding

vm_trace.c View on GitHub

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

Return the generated binding object from event

defined_class

vm_trace.c View on GitHub

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

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

trace.disable → true or false

trace.disable { block } → obj

vm_trace.c View on GitHub

          
            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, Qundef,
                         previous_tracing ? rb_tracepoint_enable : rb_tracepoint_disable,
                         tpval);
    }
    else {
        return previous_tracing ? Qtrue : Qfalse;
    }
}

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

trace.enable → true or false

trace.enable { block } → obj

vm_trace.c View on GitHub

          
            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, Qundef,
                         previous_tracing ? rb_tracepoint_enable : rb_tracepoint_disable,
                         tpval);
    }
    else {
        return previous_tracing ? Qtrue : Qfalse;
    }
}

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

trace.enabled? → true or false

vm_trace.c View on GitHub

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

The current status of the trace

event

vm_trace.c View on GitHub

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

Type of event

See Events at TracePoint for more information.

trace.inspect → string

vm_trace.c View on GitHub

          
            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");
    }
}

Return a string containing a human-readable TracePoint status.

lineno

vm_trace.c View on GitHub

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

Line number of the event

method_id

vm_trace.c View on GitHub

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

Return the name of the method being called

path

vm_trace.c View on GitHub

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

Path of the file being run

raised_exception

vm_trace.c View on GitHub

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

Value from exception raised on the :raise event

return_value

vm_trace.c View on GitHub

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

Return value from :return, c_return, and b_return event

self

vm_trace.c View on GitHub

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

Return the trace object during event

Same as TracePoint#binding:

trace.binding.eval('self')