sem_post

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
       For an explanation of the terms used in this section, see
       attributes(7).

       ┌───────────┬───────────────┬─────────┐
       │Interface  Attribute     Value   │
       ├───────────┼───────────────┼─────────┤
       │sem_post() │ Thread safety │ MT-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) and shm_open(3).

SEE ALSO
       sem_getvalue(3), sem_wait(3), sem_overview(7), signal-safety(7)

COLOPHON
       This page is part of release 5.06 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
       https://www.kernel.org/doc/man-pages/.



Linux                             2020-04-11                       SEM_POST(3)