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Class: TracePoint

Relationships & Source Files
Inherits: Object
Defined in: vm_trace.c

Overview

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

Class Method Summary

Instance Attribute Summary

Instance Method Summary

Constructor Details

.new(*events) {|obj| ... } ⇒ Object

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 TracePoint@Events 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.

Class Method Details

.stat ⇒ Object

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.

.trace(*events) {|obj| ... } ⇒ Object

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

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

trace.enabled? #=> true

Instance Attribute Details

#enabled? ⇒ Boolean (readonly)

The current status of the trace

Instance Method Details

#binding

Return the generated binding object from event

#defined_class

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

#disable ⇒ Boolean #disable ⇒ Object

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

#enable ⇒ Boolean #enable ⇒ Object

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

#event

Type of event

See TracePoint@Events for more information.

#inspect ⇒ String

Return a string containing a human-readable TracePoint status.

#lineno

Line number of the event

#method_id

Return the name of the method being called

#path

Path of the file being run

#raised_exception

Value from exception raised on the :raise event

#return_value

Return value from :return, c_return, and b_return event

#self

Return the trace object during event

Same as #binding:

trace.binding.eval('self')