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NAME

       sem_post - unlock a semaphore

SYNOPSIS

       #include <semaphore.h>

       int sem_post(sem_t *sem);

       Link with -lrt or -pthread.

DESCRIPTION

       sem_post()  increments  (unlocks)  the semaphore pointed to by sem.  If
       the semaphore’s value consequently  becomes  greater  than  zero,  then
       another  process  or thread blocked in a sem_wait(3) call will be woken
       up and proceed to lock the semaphore.

RETURN VALUE

       sem_post() returns 0 on success; on error, the value of  the  semaphore
       is  left  unchanged,  -1  is returned, and errno is set to indicate the
       error.

ERRORS

       EINVAL sem is not a valid semaphore.

       EOVERFLOW
              The maximum allowable value for a semaphore would be exceeded.

CONFORMING TO

       POSIX.1-2001.

NOTES

       sem_post() is async-signal-safe: it  may  be  safely  called  within  a
       signal handler.

EXAMPLE

       See sem_wait(3).

SEE ALSO

       sem_getvalue(3), sem_wait(3), sem_overview(7)

COLOPHON

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