NAME

       sem_getvalue - get the value of a semaphore

SYNOPSIS

       #include <semaphore.h>

       int sem_getvalue(sem_t *sem, int *sval);

       Link with -pthread.

DESCRIPTION

       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),  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).  Linux adopts the former behavior.

RETURN VALUE

       sem_getvalue() returns 0 on success; on error, -1 is returned and errno is set to indicate the error.

ERRORS

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

ATTRIBUTES

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

       ┌───────────────┬───────────────┬─────────┐
       │Interface      │ Attribute     │ Value   │
       ├───────────────┼───────────────┼─────────┤
       │sem_getvalue() │ Thread safety │ MT-Safe │
       └───────────────┴───────────────┴─────────┘

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

NOTES

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

SEE ALSO

       sem_post(3), sem_wait(3), sem_overview(7)

COLOPHON

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