Pthreads on Linux encourage holding the lock during a signal or broadcast (http://linux.die.net/man/3/pthread_cond_signal http://linux.die.net/man/3/pthread_con

Pthreads on Linux encourage holding the lock during a signal or broadcast (http://linux.die.net/man/3/pthread_cond_signal http://linux.die.net/man/3/pthread_cond_signal): The pthread_cond_broadcast() or pthread_cond_signal() functions may be called by a thread whether or not it currently owns the mutex that threads calling pthread_cond_wait() or pthread_cond_timedwait() have associated with the condition variable during their waits; however, if predictable scheduling behavior is required, then that mutex shall be locked by the thread calling pthread_cond_broadcast() or pthread_cond_signal(). They don't define what exactly "predictable scheduling is", but the message that most programmers will probably come away with is, grabbing the lock is probably the better thing to do.