Use cond_signal(3C) to unblock one thread that is blocked on the condition variable pointed to by cv . If no threads are blocked on the condition variable, cond_signal() has no effect.
#include <thread.h> int cond_signal(cond_t *cv);
cond_signal() returns 0 if successful. When the following condition is detected, cond_signal() fails and returns the corresponding value.
EFAULT
Description: cv points to an illegal address.