NAME

sem_post — increment (unlock) a semaphore

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <semaphore.h>

int
sem_post(sem_t *sem);

DESCRIPTION

The sem_post() function increments (unlocks) the semaphore pointed to by sem. If there are threads blocked on the semaphore when sem_post() is called, then the highest priority thread that has been blocked the longest on the semaphore will be allowed to return from sem_wait().

The sem_post() function is signal-reentrant and may be called within signal handlers.

RETURN VALUES

The sem_post() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

ERRORS

The sem_post() function will fail if:

[EINVAL]

The sem argument points to an invalid semaphore.

[EOVERFLOW]

The semaphore value would exceed SEM_VALUE_MAX.

SEE ALSO

sem_getvalue(3), sem_trywait(3), sem_wait(3)

STANDARDS

The sem_post() function conforms to ISO/IEC 9945-1:1996 (“POSIX.1”).