# frozen_string_literal: false
# Outputs a source level execution trace of a Ruby program.
# It does this by registering an event handler with Kernel#set_trace_func for
# processing incoming events. It also provides methods for filtering unwanted
# trace output (see Tracer.add_filter, Tracer.on, and Tracer.off).
# Consider the following Ruby script
# Running the above script using <code>ruby -r tracer example.rb</code> will
# output the following trace to STDOUT (Note you can also explicitly
# <code>require 'tracer'</code>)
# #0:<internal:lib/rubygems/custom_require>:38:Kernel:<: -
# #0:example.rb:3::-: class A
# #0:example.rb:3::C: class A
# #0:example.rb:4::-: def square(a)
# #0:example.rb:7::E: end
# #0:example.rb:9::-: a = A.new
# #0:example.rb:10::-: a.square(5)
# #0:example.rb:4:A:>: def square(a)
# #0:example.rb:5:A:-: return a*a
# #0:example.rb:6:A:<: end
# | | | | ---------------------+ event
# | | | ------------------------+ class
# | | --------------------------+ line
# | ------------------------------------+ filename
# ---------------------------------------+ thread
# Symbol table used for displaying incoming events:
# +}+:: call a C-language routine
# +{+:: return from a C-language routine
# +>+:: call a Ruby method
# +C+:: start a class or module definition
# +E+:: finish a class or module definition
# +-+:: execute code on a new line
# +^+:: raise an exception
# +<+:: return from a Ruby method
# by Keiju ISHITSUKA(keiju@ishitsuka.com)
# display additional debug information (defaults to false)
# output stream used to output trace (defaults to STDOUT)
# mutex lock used by tracer for displaying trace output
attr_reader :stdout_mutex
# display process id in trace output (defaults to false)
attr_accessor :display_process_id
alias display_process_id? display_process_id
# display thread id in trace output (defaults to true)
attr_accessor :display_thread_id
alias display_thread_id? display_thread_id
# display C-routine calls in trace output (defaults to false)
attr_accessor :display_c_call
alias display_c_call? display_c_call
Tracer::display_process_id = false
Tracer::display_thread_id = true
Tracer::display_c_call = false
@stdout_mutex = Thread::Mutex.new
# Symbol table used for displaying trace information
@threads[Thread.main.object_id] = 0
@threads[Thread.current.object_id] = 0
set_trace_func method(:trace_func).to_proc
stdout.print "Trace on\n" if Tracer.verbose?
stdout.print "Trace off\n" if Tracer.verbose?
def add_filter(p = nil, &b) # :nodoc:
def set_get_line_procs(file, p = nil, &b) # :nodoc:
@get_line_procs[file] = p
def get_line(file, line) # :nodoc:
if p = @get_line_procs[file]
unless list = SCRIPT_LINES__[file]
list = File.readlines(file) rescue []
SCRIPT_LINES__[file] = list
def get_thread_no # :nodoc:
if no = @threads[Thread.current.object_id]
@threads[Thread.current.object_id] = @threads.size
def trace_func(event, file, line, id, binding, klass, *) # :nodoc:
return if file == __FILE__
return unless p.call event, file, line, id, binding, klass
return unless Tracer::display_c_call? or
event != "c-call" && event != "c-return"
Tracer::stdout_mutex.synchronize do
stdout.printf("<%d>", $$) if Tracer::display_process_id?
stdout.printf("#%d:", get_thread_no) if Tracer::display_thread_id?
source = get_line(file, line)
stdout.printf("%s:%d:%s:%s: %s",
# Reference to singleton instance of Tracer
# You can also pass a block:
# # trace everything in this block
# Register an event handler <code>p</code> which is called every time a line
# in +file_name+ is executed.
# Tracer.set_get_line_procs("example.rb", lambda { |line|
# puts "line number executed is #{line}"
def Tracer.set_get_line_procs(file_name, p = nil, &b)
Single.set_get_line_procs(file_name, p)
# Used to filter unwanted trace output
# Example which only outputs lines of code executed within the Kernel class:
# Tracer.add_filter do |event, file, line, id, binding, klass, *rest|
def Tracer.add_filter(p = nil, &b)
SCRIPT_LINES__ = {} unless defined? SCRIPT_LINES__
# call Tracer.on only if required by -r command-line option
count = caller.count {|bt| %r%/rubygems/core_ext/kernel_require\.rb:% !~ bt}
if (defined?(Gem) and count == 0) or
(!defined?(Gem) and count <= 1)