sem_trywait(2) — DG/UX 5.4R3.00



sem_trywait(2)                 DG/UX 5.4R3.00                 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.




Licensed material--property of copyright holder(s)                         1



sem_trywait(2)                 DG/UX 5.4R3.00                 sem_trywait(2)


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






















































Licensed material--property of copyright holder(s)                         2

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