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SEM_WAIT(3) Library Functions Manual SEM_WAIT(3)

sem_wait, sem_trywaitdecrement (lock) a semaphore

library “libpthread”

#include <semaphore.h>

int
sem_wait(sem_t *sem);

int
sem_trywait(sem_t *sem);

The () function decrements (locks) the semaphore pointed to by sem, but blocks if the value of sem is zero, until the value is non-zero and the value can be decremented.

The () function decrements (locks) the semaphore pointed to by sem only if the value is non-zero. Otherwise, the semaphore is not decremented and an error is returned.

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

sem_wait() and sem_trywait() will fail if:

[]
sem points to an invalid semaphore.

Additionally, sem_trywait() will fail if:

[]
The semaphore value was zero, and thus could not be decremented.

sem_post(3)

sem_wait() and sem_trywait() conform to ISO/IEC 9945-1:1996 (“POSIX.1”).

April 15, 2009 DragonFly-5.6.1