class TracePoint

In general, while a TracePoint callback is running, other registered callbacks are not called to avoid confusion by reentrance. This method allows the reentrance in a given block. This method should be used carefully, otherwise the callback can be easily called infinitely.

If this method is called when the reentrance is already allowed, it raises a RuntimeError.

Example:

# Without reentry
# ---------------

line_handler = TracePoint.new(:line) do |tp|
  next if tp.path != __FILE__ # only work in this file
  puts "Line handler"
  binding.eval("class C; end")
end.enable

class_handler = TracePoint.new(:class) do |tp|
  puts "Class handler"
end.enable

class B
end

# This script will print "Class handler" only once: when inside :line
# handler, all other handlers are ignored

# With reentry
# ------------

line_handler = TracePoint.new(:line) do |tp|
  next if tp.path != __FILE__ # only work in this file
  next if (__LINE__..__LINE__+3).cover?(tp.lineno) # don't be invoked from itself
  puts "Line handler"
  TracePoint.allow_reentry { binding.eval("class C; end") }
end.enable

class_handler = TracePoint.new(:class) do |tp|
  puts "Class handler"
end.enable

class B
end

# This wil print "Class handler" twice: inside allow_reentry block in :line
# handler, other handlers are enabled.

Note that the example shows the principal effect of the method, but its practical usage is for debugging libraries that sometimes require other libraries hooks to not be affected by debugger being inside trace point handling. Precautions should be taken against infinite recursion in this case (note that we needed to filter out calls by itself from :line handler, otherwise it will call itself infinitely).

# File trace_point.rb, line 198
def self.allow_reentry
  Primitive.tracepoint_allow_reentry
end

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 an ArgumentError 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.lineno #=> access from outside (RuntimeError)

Access from other threads is also forbidden.

# File trace_point.rb, line 96
def self.new(*events)
  Primitive.tracepoint_new_s(events)
end

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.

# File trace_point.rb, line 118
def self.stat
  Primitive.tracepoint_stat_s
end

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

# File trace_point.rb, line 133
def self.trace(*events)
  Primitive.tracepoint_trace_s(events)
end

Return the generated binding object from event.

Note that for :c_call and :c_return events, the method will return nil, since C methods themselves do not have bindings.

# File trace_point.rb, line 381
def binding
  Primitive.tracepoint_attr_binding
end

Return the called name of the method being called

# File trace_point.rb, line 337
def callee_id
  Primitive.tracepoint_attr_callee_id
end

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

# File trace_point.rb, line 373
def defined_class
  Primitive.tracepoint_attr_defined_class
end

Deactivates the trace

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

trace.enabled?      #=> true
trace.disable       #=> true (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

# File trace_point.rb, line 296
def disable
  Primitive.tracepoint_disable_m
end

Activates the trace.

Returns true if trace was enabled. Returns 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 during the block call. If target and target_line are both nil, then target_thread will default to the current thread if a block is given.

trace.enabled?
#=> false

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

trace.enabled?
#=> false

target, target_line and target_thread parameters are used to limit tracing only to specified code objects. target should be a code object for which RubyVM::InstructionSequence.of will return an instruction sequence.

t = TracePoint.new(:line) { |tp| p tp }

def m1
  p 1
end

def m2
  p 2
end

t.enable(target: method(:m1))

m1
# prints #<TracePoint:line test.rb:4 in `m1'>
m2
# prints nothing

Note: You cannot access event hooks within the enable block.

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

# File trace_point.rb, line 260
def enable(target: nil, target_line: nil, target_thread: :default)
  Primitive.tracepoint_enable_m(target, target_line, target_thread)
end

The current status of the trace

# File trace_point.rb, line 304
def enabled?
  Primitive.tracepoint_enabled_p
end

Compiled source code (String) on *eval methods on the :script_compiled event. If loaded from a file, it will return nil.

# File trace_point.rb, line 407
def eval_script
  Primitive.tracepoint_attr_eval_script
end

Type of event

See Events at TracePoint for more information.

# File trace_point.rb, line 311
def event
  Primitive.tracepoint_attr_event
end

Return a string containing a human-readable TracePoint status.

# File trace_point.rb, line 105
def inspect
  Primitive.tracepoint_inspect
end

Compiled instruction sequence represented by a RubyVM::InstructionSequence instance on the :script_compiled event.

Note that this method is MRI specific.

# File trace_point.rb, line 415
def instruction_sequence
  Primitive.tracepoint_attr_instruction_sequence
end

Line number of the event

# File trace_point.rb, line 316
def lineno
  Primitive.tracepoint_attr_lineno
end

Return the name at the definition of the method being called

# File trace_point.rb, line 332
def method_id
  Primitive.tracepoint_attr_method_id
end

Return the parameters definition of the method or block that the current hook belongs to. Format is the same as for Method#parameters

# File trace_point.rb, line 327
def parameters
  Primitive.tracepoint_attr_parameters
end

Path of the file being run

# File trace_point.rb, line 321
def path
  Primitive.tracepoint_attr_path
end

Value from exception raised on the :raise event, or rescued on the :rescue event.

# File trace_point.rb, line 401
def raised_exception
  Primitive.tracepoint_attr_raised_exception
end

Return value from :return, :c_return, and :b_return event

# File trace_point.rb, line 396
def return_value
  Primitive.tracepoint_attr_return_value
end

Return the trace object during event

Same as the following, except it returns the correct object (the method receiver) for :c_call and :c_return events:

trace.binding.eval('self')

# File trace_point.rb, line 391
def self
  Primitive.tracepoint_attr_self
end