std::condition_variable::notify_one() called several times without context switching

Question

How many waiting threads will wake up in this example:

1st thread:

void wakeUp2Threads()
{
    std::unique_lock lo         


        

Answer 1

The notify_one call atomically unblocks one thread. That means that when called a second time it can't unblock the same thread as it's no longer blocked.

This is specified in the standard at section 30.5/3 and 30.5.1/7.