id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
1950	pthread/condition_variable::wait() unlocks associated mutex prematurely and may miss a notification	Stas Maximov <smaximov@…>	Anthony Williams	"pthread implementation of class condition_variable implements wait() is as follows:

template<typename lock_type>
void wait(lock_type& m)
{
    int res=0;
    {
        detail::interruption_checker check_for_interruption(&cond);
        {
            boost::pthread::pthread_mutex_scoped_lock internal_lock(&internal_mutex);
            m.unlock();
            res=pthread_cond_wait(&cond,&internal_mutex);
        }
        m.lock();
    }
    if(res)
    {
        throw condition_error();
    }
}

Each condition variable must have an associated mutex. pthread_cond_wait() must enter with the mutex locked. Having the mutex locked guarantees that no notifications will be missed by the receiving thread.

The above implementation releases mutex before entering pthread_cond_wait(). This creates an opportunity for pre-emption of the thread just after the mutex was unlocked, but before pthread has been entered. If another thread pre-empts at this point and tries to notify this condition variable, this notification will be missed by this thread. 

Substitution of some random, unrelated mutex into pthread_cond_wait() is not a solution. It is the original mutex that is associated with the condition that must be passed to pthread_cond_wait().
"	Bugs	closed	Boost 1.36.0	thread	Boost 1.35.0	Showstopper	invalid	pthread_cond_wait condition variable pthread mutex