i want write simple multithreaded program making use of conditional variables in c.
i want have main thread (thread a) sleeps 5 sec , wake waiting clients (therads b, possible many) print message. should repeated time.
i have read manual don't understand why not work. let's assume have variables given threads via pointers (properly, have checked that):
pthread_mutex_t* mutex; pthread_cond_t* cond; int* variable; i have following code:
thread (sleeping):
while(1) { lockmutex(mutex); (*variable) = 1; pthread_cond_broadcast(cond); unlockmutex(mutex); sleep(5); lockmutex(mutex); (*variable) = 0; pthread_cond_broadcast(cond); unlockmutex(mutex); } thread b (printing):
while(1) { lockmutex(mutex); while((*variable) == 1) pthread_cond_wait(cond, mutex); unlockmutex(mutex); fprintf("active thread! number: %d\n", id); lockmutex(mutex); while((*(variable))==0) pthread_cond_wait(cond, mutex); unlockmutex(mutex); } i don't have deadlock, unfortunatelly doesn't work expected. can give me explanation should do? grateful help.
the problem thread setting *variable = 1 before of sleeping threads have chance see 0. because condition variable wake waiting threads doesn't mean woken threads scheduled fast enough prevent thread writing *variable again.
