Re: [Boost-bugs] [Boost C++ Libraries] #7422: condition_variable performance regression

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #7422: condition_variable performance regression
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-09-26 19:05:06

#7422: condition_variable performance regression
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  Reporter:  maxim.yegorushkin@…          |       Owner:  anthonyw          
      Type:  Bugs                         |      Status:  new               
 Milestone:  To Be Determined             |   Component:  thread            
   Version:  Boost 1.51.0                 |    Severity:  Regression        
Resolution:                               |    Keywords:  condition_variable
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Comment (by viboes):

 Replying to [ticket:7422 maxim.yegorushkin@…]:
 > In boost versions prior to 1.45 condition_variable was a zero-overhead
 thin wrapper over pthread_cond_t.
 >
 > In version 1.45 an internal mutex was added to condition_variable to
 improve thread cancellation support as described elsewhere (can't add the
 link to gmane archive because Trac thinks it's spam).
 >
 > Since version 1.45 calling condition_variable::wait*() and
 condition_variable::notify*() lock the internal mutex. Doing so causes
 performance regressions for latency sensitive applications that don't use
 thread cancellation. To put it in other words, condition_variable was
 essentially turned into condition_variable_any.
 >
 > Could the old version of condition_variable be added back please?

 As Anthony explained in the link you mention, we can not do that without
 breaking existing code. I don't know if defining an additional
 basic_condition_variable will respond to you expectations.

 In any case, I don't see as a bug, except if you can find in the
 documentation a reference to the zero-overhead.

 > A good idea seems to be requiring a macro, for example
 BOOST_THREADS_REQUIRE_THREAD_CANCELLATION, to be defined for
 condition_variable to include the internal mutex or be an alias for
 condition_variable_any. A call to thread::interrupt() would fail at
 compile time if BOOST_THREADS_REQUIRE_THREAD_CANCELLATION is not defined.
 Things may get more complicated if any compiled boost libraries use
 condition_variable though.

 Well this is a different feature that should merit a specific ticket.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7422#comment:1>
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