sem_getvalue(3) - Linux manual page (original) (raw)

semgetvalue(3) Library Functions Manual semgetvalue(3)

NAME top

   sem_getvalue - get the value of a semaphore

LIBRARY top

   POSIX threads library (_libpthread_, _-lpthread_)

SYNOPSIS top

   **#include <semaphore.h>**

   **int sem_getvalue(sem_t *restrict** _sem_**, int *restrict** _sval_**);**

DESCRIPTION top

   **sem_getvalue**() places the current value of the semaphore pointed
   to _sem_ into the integer pointed to by _sval_.

   If one or more processes or threads are blocked waiting to lock
   the semaphore with [sem_wait(3)](../man3/sem%5Fwait.3.html), POSIX.1 permits two possibilities
   for the value returned in _sval_: either 0 is returned; or a
   negative number whose absolute value is the count of the number of
   processes and threads currently blocked in [sem_wait(3)](../man3/sem%5Fwait.3.html).  Linux
   adopts the former behavior.

RETURN VALUE top

   **sem_getvalue**() returns 0 on success; on error, -1 is returned and
   _[errno](../man3/errno.3.html)_ is set to indicate the error.

ERRORS top

   **EINVAL** _sem_ is not a valid semaphore.  (The glibc implementation
          currently does not check whether _sem_ is valid.)

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────────┼───────────────┼─────────┤
   │ **sem_getvalue**()                       │ Thread safety │ MT-Safe │
   └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

   POSIX.1-2008.

HISTORY top

   POSIX.1-2001.

NOTES top

   The value of the semaphore may already have changed by the time
   **sem_getvalue**() returns.

SEE ALSO top

   [sem_post(3)](../man3/sem%5Fpost.3.html), [sem_wait(3)](../man3/sem%5Fwait.3.html), [sem_overview(7)](../man7/sem%5Foverview.7.html)

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Linux man-pages 6.10 2024-07-23 semgetvalue(3)

Pages that refer to this page:sem_close(3), sem_open(3), sem_post(3), sem_unlink(3), sem_wait(3), sem_overview(7)