Re: [Boost-bugs] [Boost C++ Libraries] #5331: usage of deprecated swp instruction on arm

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #5331: usage of deprecated swp instruction on arm
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-01-19 10:12:53

#5331: usage of deprecated swp instruction on arm
----------------------------------------------------------+-----------------
  Reporter:  Boaz Ben-David <boaz.bd@…>                   |       Owner:  pdimov        
      Type:  Bugs                                         |      Status:  new           
 Milestone:  To Be Determined                             |   Component:  smart_ptr     
   Version:  Boost 1.46.0                                 |    Severity:  Problem       
Resolution:                                               |    Keywords:  arm deprecated
----------------------------------------------------------+-----------------

Comment (by abel@…):

 Hi,

 I'm not sure if this is still on the agenda or not. However, I had to fix
 this specific problem earlier this year. I followed the outline given at
 http://www.boost.org/support/bugs.html to produce the attached patch
 against the latest trunk.

 The patch should take care of deprecation warnings.

 The latest trunk introduced a memory barrier after the swp instructiopn.
 However, I think using a memory barrier is only ever necessary when the
 lock was actually acquired. Yet, the trunk codebase sets one up on each
 call of try_lock()... This might have some performance implications.

 As of right now, try_lock() is called in lock() inside a loop which
 explicitly yields the thread if try_lock() failed. It might be better to
 have that loop in try_lock() instead and only do a dmb if the lock was
 acquired. However, this might change the API in more ways than most people
 would be comfortable with, I guess...

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5331#comment:2>
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