This is only implemented for OSes that provide a way to perform a timed join. For all other OSes, we stick to the previous implementation, which as the comment indicates, may run for arbitrarily long time after wait() has returned, running user code (e.g., pthread_setspecific() and thread_local destructors). Instead, if we perform the joining, we are assured by pthread and the OS that the thread has exited and no user code remains running. Unfortunately, this only applies to non-adopted threads, because we can't pthread_join() a thread we didn't start. As of this writing, this code only applies to Linux/glibc. MUSL, Bionic and several BSDs have pthread_timedjoin, but that takes a CLOCK_REALTIME absolute time, which means it's subject to time jumps, while QWaitCondition can sometimes use the monotonic clock in those systems. Change-Id: I692e24d7411742447e10fffd650fe84f6a9cdedd Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>