rbtrace: like strace, but for ruby code

rbtrace shows you method calls happening inside another ruby process in real time.

rbtrace works on ruby 1.8 and 1.9, running on linux or mac osx.

rbtrace is designed to have minimal overhead, and should be safe to run in production.

usage

% gem install rbtrace
% rbtrace --help

tracer types

rbtrace has several different tracing modes.

firehose: show everything

% rbtrace -p <PID> --firehose

slow: show any method calls that take longer than <N> milliseconds

% rbtrace -p <PID> --slow=<N>

methods: trace calls to specific methods

% rbtrace -p <PID> --methods "Kernel#sleep" "Proc#call"

gc: trace garbage collections

% rbtrace -p <PID> --gc

notes

--firehose is not reliable on osx.

--slow, --gc and --methods can be combined.

predefined tracers

rbtrace also includes a set of predefined tracers for popular ruby libraries and functions.

trace calls to activerecord adapters and any i/o functions

% rbtrace -p <PID> -c activerecord io

detailed example

require rbtrace into a process

% cat server.rb
require 'rbtrace'

class String
  def multiply_vowels(num)
    @test = 123
    gsub(/[aeiou]/){ |m| m*num }
  end
end

while true
  proc {
    Dir.chdir("/tmp") do
      Dir.pwd
      Process.pid
      'hello'.multiply_vowels(3)
      sleep rand*0.5
    end
  }.call
end

run the process

% ruby server.rb &
[1] 87854

trace a function using the process's pid

% rbtrace -p 87854 -m sleep
*** attached to process 87854

Kernel#sleep <0.138615>
Kernel#sleep <0.147726>
Kernel#sleep <0.318728>
Kernel#sleep <0.338173>
Kernel#sleep <0.373004>
Kernel#sleep
*** detached from process 87854

trace everything

% rbtrace -p 87854 --firehose
*** attached to process 87938

Kernel#proc <0.000082>
Proc#call
   Dir.chdir
      Dir.pwd <0.000060>
      Process.pid <0.000021>
      String#multiply_vowels
         String#gsub
            String#* <0.000023>
            String#* <0.000022>
         String#gsub <0.000127>
      String#multiply_vowels <0.000175>
      Kernel#rand <0.000018>
      Float#* <0.000022>
      Kernel#sleep <0.344281>
   Dir.chdir <0.344858>
Proc#call <0.344908>
*** detached from process 87938

trace specific functions

% rbtrace -p 87854 -m sleep Dir.chdir Dir.pwd Process.pid "String#gsub" "String#*"
*** attached to process 87854

Dir.chdir
   Dir.pwd <0.000023>
   Process.pid <0.000008>
   String#gsub
      String#* <0.000008>
      String#* <0.000007>
   String#gsub <0.000050>
   Kernel#sleep <0.498809>
Dir.chdir <0.499025>

Dir.chdir
   Dir.pwd <0.000024>
   Process.pid <0.000008>
   String#gsub
      String#* <0.000008>
      String#* <0.000007>
   String#gsub <0.000050>
   Kernel#sleep
*** detached from process 87854

trace all functions in a class/module

% rbtrace -p 87854 -m "Kernel#"
*** attached to process 87854

Kernel#proc <0.000062>
Kernel#rand <0.000010>
Kernel#sleep <0.218677>
Kernel#proc <0.000016>
Kernel#rand <0.000010>
Kernel#sleep <0.195914>
Kernel#proc <0.000016>
Kernel#rand <0.000009>
Kernel#sleep
*** detached from process 87854

get values of variables and other expressions

% rbtrace -p 87854 -m "String#gsub(self, @test)" "String#*(self, __source__)" "String#multiply_vowels(self, self.length, num)"
*** attached to process 87854

String#multiply_vowels(self="hello", self.length=5, num=3)
   String#gsub(self="hello", @test=123)
      String#*(self="e", __source__="server.rb:6") <0.000020>
      String#*(self="o", __source__="server.rb:6") <0.000018>
   String#gsub <0.000085>
String#multiply_vowels <0.000198>

String#multiply_vowels(self="hello", self.length=5, num=3)
   String#gsub(self="hello", @test=123)
      String#*(self="e", __source__="server.rb:6") <0.000020>
      String#*(self="o", __source__="server.rb:6") <0.000020>
   String#gsub <0.000102>
String#multiply_vowels <0.000218>

*** detached from process 87854

watch for method calls slower than 250ms

% rbtrace -p 87854 --slow=250
*** attached to process 87854
      Kernel#sleep <0.459628>
   Dir.chdir <0.459828>
Proc#call <0.459849>

      Kernel#sleep <0.484666>
   Dir.chdir <0.484804>
Proc#call <0.484818>

*** detached from process 87854

todo

• add triggers to start tracing slow methods only inside another method
• add watch expressions to fire tracers only when an expression is true
• add special expressions for method args (arg0, arguments)
• optimize local variable lookup to avoid instance_eval
• investigate mach_msg on osx since msgget(2) has hard kernel limits