Hands-On System Programming with Linux

Using the condition variable

The correct approach is to use a CV. A condition variable is a way for threads to synchronize upon the value of data in an efficient manner. It achieves the same end result as the naive polling approach does, but in a far more efficient and, even more importantly, correct manner.

Check out the following table:

Time	Thread B	Thread A
t0	Initialize: gWorkDone = 0 ; init the {CV, mutex} pair	< common >
t1	Wait upon signal from thread B : lock the associated mutex; pthread_cond_wait()
t2	Perform the work ...	< ... blocking ... >
t3	Work done; lock the associated mutex; signal thread A : pthread_cond_signal() ; unlock the associated mutex	...
t4	Unblocked; check to see that the work is really done, ...