SEM_POST(3)                         Linux Programmer's Manual                         SEM_POST(3)



NAME
       sem_post - unlock a semaphore

SYNOPSIS
       #include <semaphore.h>

       int sem_post(sem_t *sem);

       Link with -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.

ATTRIBUTES
   Multithreading (see pthreads(7))
       The sem_post() function is thread-safe.

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
       This page is part of release 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.



Linux                                       2014-02-26                                SEM_POST(3)