[Boost-bugs] [Boost C++ Libraries] #10163: Boost.Signal2 performs too many locks in a multi-threaded environment where the life cycle of the source and target are the duration of the program

Subject: [Boost-bugs] [Boost C++ Libraries] #10163: Boost.Signal2 performs too many locks in a multi-threaded environment where the life cycle of the source and target are the duration of the program
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-06-30 19:31:50

#10163: Boost.Signal2 performs too many locks in a multi-threaded environment where
the life cycle of the source and target are the duration of the program
-----------------------------------------+--------------------------
 Reporter:  Dave Gotwisner <dgotwisn@…>  |      Owner:  fmhess
     Type:  Bugs                         |     Status:  new
Milestone:  To Be Determined             |  Component:  signals2
  Version:  Boost 1.54.0                 |   Severity:  Optimization
 Keywords:                               |
-----------------------------------------+--------------------------
 Boost.Signal2 requires that the receiver be a shared_ptr, or a weak_ptr.

 If the life cycle of the receiver is the length of the program (ie,
 created rather than new'ed as a global object), there is no need to
 reference count the pointer.  On Linux/X86_64, the act of making it a
 shared pointer (to protect it from going away underneath us) causes an
 atomic increment and decrement of the reference counter, which causes high
 CPU utilization in the atomic lock/unlock when performing lots of signals
 in parallel across multiple threads.

 It would be nice to have a non-shared_ptr interface to eliminate the
 refrence count bottle neck, as the management of the pointer is higher
 overhead than actually doing the signal, in many cases.

 This was found with a program that has multiple threads signalling very
 small objects at a very high rate, and looking at the underlying system
 with both gprof and pprof.  In our test case, 48% of the gprof time was
 spent in the atomic lock/unlock/test code.

 Because of the proprietary nature of our code, I can't attach a sample.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/10163>
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