sem_trylock(2) — DG/UX 5.4R2.01



sem_trylock(2)               DG/UX 5.4 Rel. 2.01              sem_trylock(2)


NAME
       sem_trylock - lock an available semaphore

SYNOPSIS
       #include <semaphore.h>

       int semtrylock (*sem)
            semt  *sem;

DESCRIPTION
       Use semtrylock(2) to lock a semaphore, making it unavailable to
       other processes: sem is a valid semaphore descriptor returned by a
       prior seminit(2) call. Once locked, a semaphore stays locked until
       unlocked with semunlock(2). Thus, if your process locks a semaphore
       and then calls semdestroy(2), exit(2), or exec(2), the semaphore
       (provided it still exists) remains locked.

       If the semaphore is unavailable, semtrylock returns immediately with
       an error.  Otherwise, the semaphore is locked.  For a blocking lock
       operation (block until the semaphore is available, then lock it), use
       semlock(2).

       Locking a semaphore decrements its value specified with seminit(2)
       and unlocking it increments the value. This call succeeds when the
       semaphore's value is greater than 0, which defines availability.

   Note
        * This routine is based on POSIX realtime extension document P1003.4
          draft 12. It is therefore subject to change.

        * Compilation of a source file using this routine requires that
          feature macro _POSIX4_DRAFT_SOURCE be defined.  This feature macro
          is not enabled by any other feature macro, nor does it enable any
          other feature macro.

        * The compiled routine must be linked to library librte.a.

RETURN VALUE
       If successful, semlock returns 0. If unsuccessful, it returns -1 and
       sets ERRNO to one of the following:

        EAGAIN The semaphore is already locked.

        EFAULT Unable to access the internal structures.

        EINVAL sem is invalid.

SEE ALSO
       semdestroy(2), seminit(2), semlock(2), semunlink(2),
       semunlock(2).







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