To avoid this sequence of events, insert lock and unlock statements in put and get routines so that the number of keys missing is always 0. The relevant pthread calls are (for more see the manual pages, man pthread):

pthread_mutex_t lock; // declare a lock

pthread_mutex_init(&lock, NULL); // initialize the lock

pthread_mutex_lock(&lock); // acquire lock

pthread_mutex_unlock(&lock); // release lock

Test your code first with 1 thread, then test it with 2 threads. Is it correct (i.e. have you eliminated missing keys?)? Is the two-threaded version faster than the single-threaded version?

I just want a general answer.