NAME

       sem_getvalue - get the value of a semaphore

LIBRARY

       POSIX threads library (libpthread, -lpthread)

SYNOPSIS

       #include <semaphore.h>

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

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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       POSIX.1-2008.

HISTORY

       POSIX.1-2001.

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)