rw_wrlock(3synch)                                  rw_wrlock(3synch)


       NAME
             rw_wrlock - acquire a reader-writer lock in write mode

       SYNOPSIS
             cc [options] -Kthread file
             #include <synch.h>
             int rw_wrlock(rwlock_t *lock);

          Parameters
             lock  pointer to the reader-writer lock to be acquired

       DESCRIPTION
             rw_wrlock acquires the reader-writer lock pointed to by lock
             in write mode.

             Only one writer at a time can hold a reader-writer lock,
             although any number of readers can hold the lock at any time.
             Once a writer has requested the lock with rw_wrlock, all
             subsequent requests for the lock in either read or write mode
             are blocked.

             When no other readers or writers hold the lock, rw_wrlock will
             acquire the lock, and the caller will proceed.  Any other
             write and read requests for the lock will block until the
             caller unlocks the lock with rw_unlock(3synch).

             If the lock is held by any readers when rw_wrlock is called,
             and no writer is waiting for the lock, the caller blocks until
             all the current readers have released the lock.  If the lock
             is held by another writer, or if there are any other writers
             already waiting for the lock, the caller blocks to wait for
             the lock.

             lock must previously have been initialized (see rwlock_init).

             From the point of view of the application, this function is
             atomic: even if interrupted by a signal or forkall, rw_wrlock
             will not return until it holds the lock.  As a consequence, if
             rw_wrlock is interrupted, an error indication such as EINTR is
             never returned to the user.

          Return Values
             rw_wrlock returns zero for success and an error number for
             failure, as described below.




                           Copyright 1994 Novell, Inc.               Page 1

      rw_wrlock(3synch)                                  rw_wrlock(3synch)


         Errors
            If any of the following conditions is detected, rw_wrlock
            returns the corresponding value:

            EINVAL   Invalid argument specified.

            ENOMEM   Insufficient memory

      USAGE
            For consistency, locks acquired with rw_rdlock should be
            released with rw_unlock.

         Warnings
            If a thread exits while holding a reader-writer lock, the lock
            will not be unlocked, and other threads waiting for the lock
            will wait forever.  Similarly, if a process exits while
            holding a USYNC_PROCESS reader-writer lock, the lock will not
            be unlocked, and other processes waiting for the reader-writer
            lock will wait forever.

      REFERENCES
            rwlock(3synch), rwlock_destroy(3synch), rwlock_init(3synch),
            rw_rdlock(3synch), rw_tryrdlock(3synch), rw_trywrlock(3synch),
            rw_unlock(3synch), synch(3synch)
























                          Copyright 1994 Novell, Inc.               Page 2