waitsem(2XNX)       (XENIX System Compatibility)       waitsem(2XNX)


       NAME
             waitsem, nbwaitsem - (XENIX) await and check access to a
             resource governed by a semaphore

       SYNOPSIS
             cc [flag . . . ] flag . . . -lx
             int waitsem(int sem_num);
             int nbwaitsem(int sem_num);

       DESCRIPTION
             waitsem gives the calling process access to the resource
             governed by the semaphore sem_num.  If the resource is in use
             by another process, waitsem will put the process to sleep
             until the resource becomes available; nbwaitsem will return
             the error ENAVAIL.  waitsem and nbwaitsem are used in
             conjunction with sigsem to allow synchronization of processes
             waiting to access a resource.  One or more processes may
             waitsem on the given semaphore and will be put to sleep until
             the process which currently has access to the resource issues
             sigsem.  sigsem causes the process which is next in line on
             the semaphore's queue to be rescheduled for execution.  The
             semaphore's queue is organized in First In, First Out (FIFO)
             order.

          Return Values
             waitsem returns the value (int) -1 if an error occurs.  If
             sem_num has not been previously opened by a call to opensem or
             creatsem, errno is set to EBADF.  If sem_num does not refer to
             a semaphore type file, errno is set to ENOTNAM.  All processes
             waiting (or attempting to wait) on the semaphore return with
             errno set to ENAVAIL when the process controlling the
             semaphore exits without relinquishing control (thereby leaving
             the resource in an undeterminate state).  If a process does
             two waitsems in a row without doing a intervening sigsem,
             errno is set to EINVAL.

       REFERENCES
             creatsem(2XNX), opensem(2XNX)










                           Copyright 1994 Novell, Inc.               Page 1