class TracePoint

Generally, while a TracePoint callback is running, other registered callbacks are not called to avoid confusion from reentrance. This method allows reentrance within a given block. Use this method carefully to avoid infinite callback invocation.

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

Example:

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

line_handler = TracePoint.new(:line) do |tp|
  next if tp.path != __FILE__ # Only works 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 the :line
# handler, all other handlers are ignored.

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

line_handler = TracePoint.new(:line) do |tp|
  next if tp.path != __FILE__ # Only works in this file
  next if (__LINE__..__LINE__+3).cover?(tp.lineno) # Prevent infinite calls
  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 will print "Class handler" twice: inside the allow_reentry block in the :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 the 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 the :line handler, otherwise it would call itself infinitely).

# File trace_point.rb, line 198
def self.allow_reentry
  Primitive.attr! :use_block
  Primitive.tracepoint_allow_reentry
end

Returns a new TracePoint object, not enabled by default.

To activate the TracePoint object, 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]
# ...

To deactivate the trace, 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 a 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 94
def self.new(*events)
  Primitive.attr! :use_block
  Primitive.tracepoint_new_s(events)
end

Returns internal information of TracePoint.

The contents of the returned value are implementation-specific and may change in the future.

This method is only for debugging TracePoint itself.

# File trace_point.rb, line 117
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 132
def self.trace(*events)
  Primitive.attr! :use_block
  Primitive.tracepoint_trace_s(events)
end

Returns the generated binding object from the event.

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

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

Returns the called name of the method being called.

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

Returns the 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 the 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 the singleton class.

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

Returns true if the trace was enabled. Returns false if the 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 disabled 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 295
def disable
  Primitive.attr! :use_block
  Primitive.tracepoint_disable_m
end

Activates the trace.

Returns true if the trace was enabled. Returns false if the 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 execution. 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

The target, target_line, and target_thread parameters are used to limit tracing 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 259
def enable(target: nil, target_line: nil, target_thread: :default)
  Primitive.attr! :use_block
  Primitive.tracepoint_enable_m(target, target_line, target_thread)
end

Returns the current status of the trace.

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

Returns the compiled source code (String) from eval methods on the :script_compiled event. If loaded from a file, it returns nil.

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

Returns the type of event.

See Events at TracePoint for more information.

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

Returns a string containing a human-readable TracePoint status.

# File trace_point.rb, line 104
def inspect
  Primitive.tracepoint_inspect
end

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

Note that this method is CRuby-specific.

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

Returns the line number of the event.

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

Returns 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

Returns the parameter definitions of the method or block that the current hook belongs to. The format is the same as for Method#parameters.

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

Returns the path of the file being executed.

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

Returns the 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

Returns the return value from :return, :c_return, and :b_return events.

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

Returns the trace object during the event.

Similar to the following, but 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