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 an expression or statement 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
:rescue
-
rescue an exception
:b_call
-
event hook at block entry
:b_return
-
event hook at block ending
:a_call
-
event hook at all calls (
call
,b_call
, andc_call
) :a_return
-
event hook at all returns (
return
,b_return
, andc_return
) :thread_begin
-
event hook at thread beginning
:thread_end
-
event hook at thread ending
:fiber_switch
-
event hook at fiber switch
:script_compiled
-
new Ruby code compiled (with
eval
,load
orrequire
)
Public Class Methods
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 ruby_3_3_3/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 ruby_3_3_3/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 ruby_3_3_3/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 ruby_3_3_3/trace_point.rb, line 133 def self.trace(*events) Primitive.tracepoint_trace_s(events) end
Public Instance Methods
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 ruby_3_3_3/trace_point.rb, line 381 def binding Primitive.tracepoint_attr_binding end
Return the called name of the method being called
# File ruby_3_3_3/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 ruby_3_3_3/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 ruby_3_3_3/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 ruby_3_3_3/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 ruby_3_3_3/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 ruby_3_3_3/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 ruby_3_3_3/trace_point.rb, line 311 def event Primitive.tracepoint_attr_event end
Return a string containing a human-readable TracePoint
status.
# File ruby_3_3_3/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 ruby_3_3_3/trace_point.rb, line 415 def instruction_sequence Primitive.tracepoint_attr_instruction_sequence end
Line number of the event
# File ruby_3_3_3/trace_point.rb, line 316 def lineno Primitive.tracepoint_attr_lineno end
Return the name at the definition of the method being called
# File ruby_3_3_3/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 ruby_3_3_3/trace_point.rb, line 327 def parameters Primitive.tracepoint_attr_parameters end
Path of the file being run
# File ruby_3_3_3/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 ruby_3_3_3/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 ruby_3_3_3/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 ruby_3_3_3/trace_point.rb, line 391 def self Primitive.tracepoint_attr_self end