[Boost-bugs] [Boost C++ Libraries] #1951: boost::interprocess::named_condition::do_wait() releases mutex prematurely, may miss notification

Subject: [Boost-bugs] [Boost C++ Libraries] #1951: boost::interprocess::named_condition::do_wait() releases mutex prematurely, may miss notification
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2008-05-26 21:27:32

#1951: boost::interprocess::named_condition::do_wait() releases mutex prematurely,
may miss notification
---------------------------------------------------------------------------------+
 Reporter:  Stas Maximov <smaximov_at_[hidden]>                                     |       Owner:  igaztanaga  
     Type:  Bugs                                                                 |      Status:  new         
Milestone:  Boost 1.36.0                                                         |   Component:  interprocess
  Version:  Boost 1.35.0                                                         |    Severity:  Showstopper 
 Keywords:  named_condition_variable interprocess sync mutex condition_variable  |  
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 Implementation of boost::interprocess::named_condition::do_wait() is shown
 below:

 template <class Lock>
 void do_wait(Lock& lock)
 {
    lock_inverter<Lock> inverted_lock(lock);
    //unlock internal first to avoid deadlock with near simultaneous waits
    scoped_lock<lock_inverter<Lock> >   external_unlock(inverted_lock);
    scoped_lock<interprocess_mutex>     internal_lock(*this->mutex());
    this->condition()->wait(internal_lock);
 }

 Lock lock is associated with the condition variable and must be released
 only inside wait(). This implementation releases the lock before it enters
 the wait(). If lock released before wait() is entered, this function may
 be pre-empted by a notifier thread, just after the lock has been released,
 but before wait() has been entered. In such case notification will be
 missed by the wait().

 Having a mutex associated with condition variable is a fundamental
 requirement. Use of another mutex (internal_lock in this case), not known
 to the notifier is not a solution. Both the receiver and the notifier,
 both must use the same CV *and* MX.

 This is like a root cause of hangs in named_condition_test on Fedora9
 running on single-cpu system under vmware-server-1.0.5.

-- 
Ticket URL: <http://svn.boost.org/trac/boost/ticket/1951>
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