sem_trywait(2) — DG/UX R4.11



sem_trywait(2)                    SDK R4.11                   sem_trywait(2)


NAME
       sem_trywait - lock an available semaphore

SYNOPSIS
       #include <semaphore.h>

       int semtrywait (*sem)
            semt  *sem;

DESCRIPTION
       Use semtrywait(2) to lock a semaphore which is currently available
       (unlocked):

        sem         is a valid semaphore address returned by a prior
                    seminit(2) or semopen(2) call.

       Locking a semaphore decrements its value, which is initially
       specified with the seminit(2) or semopen(2) call.  Unlocking a
       semaphore increments the value.

       This call locks the semaphore referenced by sem only if the semaphore
       is currently not locked; that is, if the semaphore value is currently
       positive.  Otherwise, this call does not lock the semaphore.  Once
       locked, a semaphore stays locked until it is unlocked with
       sempost(2). Thus, if your process locks a semaphore and then calls
       semclose(2), exit(2), or exec(2), the semaphore (provided it still
       exists) remains locked.

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

   Note
        * This routine is based on POSIX realtime extension document P1003.4
          draft 14. 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, semtrywait returns 0. If unsuccessful, it returns -1
       and sets ERRNO to one of the following:

        EAGAIN The semaphore is already locked, so it cannot be immediately
               locked.

        EINVAL sem is an invalid address.

        EINVAL sem is invalid.

SEE ALSO
       semdestroy(2), seminit(2), semclose(2), semopen(2),
       semunlink(2), semwait(2), sempost(2), semgetvalue(2).


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