On Wed, Dec 23, 2015 at 7:44 AM, Éric Malenfant <eric.malenfant@gmail.com> wrote:
Unless I'm missing something, the guard in condition_variable::wait does not release the mutex, it is simply there to ensure that it is reacquired on exit. The mutex is released by pthread_cond_wait (atomically with the wait on the condition).
Eric, Thank you for your reply. I believe you are incorrect that the guard only reacquires (and does not release) the mutex. The line "guard.activate(m);" indeed releases the user mutex before pthread_cond_wait (see below). You are correct that pthread_cond_wait atomically releases the mutex -- but it is releasing the internal boost mutex, not the "external" user mutex which has already been released by the guard. I assume that I am missing something, but I cannot figure out what it is. Chris === template<typename MutexType> struct lock_on_exit { MutexType* m; lock_on_exit(): m(0) {} void activate(MutexType& m_) { m_.unlock(); m=&m_; } ~lock_on_exit() { if(m) { m->lock(); } } };