Prototype: int sem_trywait(sem_t *sem);
#include <semaphore.h> sem_t sem; int ret; ret = sem_trywait(&sem); /* try to wait for semaphore*/
Use sem_trywait(3R) to try to atomically decrement the count in the semaphore pointed to by sem when the count is greater than zero. This function is a nonblocking version of sem_wait(); that is it returns immediately if unsuccessful.
sem_trywait() returns zero after completing successfully. Any other returned value indicates that an error occurred. When any of the following conditions occur, the function fails and returns the corresponding value.