Issue #6895 has been reported by ko1 (Koichi Sasada).

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Feature #6895: TracePoint API
https://bugs.ruby-lang.org/issues/6895

Author: ko1 (Koichi Sasada)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 


=begin
= Abstract

Let's introduce TracePoint API that can be replaced with set_trace_func().

= Background

See discussions on [Feature #6649] <http://bugs.ruby-lang.org/issues/show/6649>.

Problems of set_trace_func:

* Invoke trace funcs on all events (C level API can filter events)
* With this spec, we can't add new trace event (compatibility issue)
* Slow because it generates binding object each trace func

= Porposal

Introduce TracePoint API.
  
  trace = TracePoint.trace(event1, event2, ...) do |tp|
    # tp has methods like:
    #   event: event name represented by Symbol like :line.
    #          "c-call", "c-return" is :c_call, :c_return (sub('-', '_'))
    #   file, line: return filename and line number
    #   klass, id: return class or id (depends on a context. Same as set_trace_func)
    #   binding: return (generated) binding object
    #   self: new method.  same as tp.binding.eval('self')
    ... # trace func
    # tp is TracePoint object.
    # In fact, tp is same object as `trace'.
    # We don't need any object creation on trace func.
  end
  ... # Proc are called
  trace.untrace # stop tracing
  ...
  trace.retrace # restart tracing

`eventN' parameter for TracePoint.trace() is set of symbols.  You can specify events what you want to trace.  If you don't specify any events on it, then all events are activate (similar to set_trace_func).

= Implementation

See <https://github.com/ko1/ruby/compare/tracepoint>.

Try <https://github.com/ko1/ruby/tracepoint>.

= Evaluation

TracePoint API doesn't make temporary object on default.  It is faster than current set_trace_func.

  require 'benchmark'
  MAX = 1_000_000
  $c1 = $c2 = 0
  
  Benchmark.bm{|x|
    x.report{
      set_trace_func(lambda{|*args| $c1+=1})
      MAX.times{
        a = 1
      }
      set_trace_func(nil)
    }
    x.report{
      trace = TracePoint.trace(*%i{line call return c_call c_return}){|tp| $c2+=1}
      MAX.times{
        a = 1
      }
      trace.untrace
    }
    x.report{
      trace = TracePoint.trace(*%i{line call return c_call c_return}){|tp| $c2+=1; tp.event; tp.klass; tp.id}
      MAX.times{
        a = 1
      }
      trace.untrace
    }
    x.report{
      trace = TracePoint.trace(*%i{line call return c_call c_return}){|tp| $c2+=1; tp.event; tp.klass; tp.id; tp.binding}
      MAX.times{
        a = 1
      }
      trace.untrace
    }
  }
  __END__
  #=>
         user     system      total        real
   1.600000   0.000000   1.600000 (  1.601750)
   0.280000   0.000000   0.280000 (  0.287466)
   0.750000   0.000000   0.750000 (  0.741344)
   1.400000   0.020000   1.420000 (  1.420574)

= Problems

* TracePoint.trace(...) is good interface?
* Now, noway to specify Thread specific hooks (like Thread#set_trace_func)

= Next Step

I also want to introduce block enter/leave events on TracePoint.

=end




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