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



NAME
       sem_getvalue - get the value of a semaphore

SYNOPSIS
       #include <semaphore.h>

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

       Link with -lrt or -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.1-2001 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.

CONFORMING TO
       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)

COLOPHON
       This  page  is  part of release 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2006-03-25                                            SEM_GETVALUE(3)