Recall that condition variables are synchronization primitives that enable threads to wait until a particular condition occurs.

Generalizing, the combination of locks and condition variables is sometimes called a monitor, which is sometimes incorporated into data structures in some languages (note that this termi- nology is not always used in a standardized way).

Previously,we discussed howto use condition variables and signals to implement a simple producer- consumer system. Looking at this system again, could we move the signal() call in enqueue() down below the unlock()?

dequeue()
lock(A)
while (queue empty)
wait(A, C)
remove_item()
unlock(A)
enqueue()
lock(A)
insert_item()
// used to signal here, inside lock
unlock(A)
signal(C) // now signal here, outside lock

Will this work? The answer is yes. It might not be as clean conceptually, but nothing bad will happen (verify this for yourself).