rwlock_init(3synch)                              rwlock_init(3synch)


       NAME
             rwlock_init - initialize a reader-writer lock

       SYNOPSIS
             cc [options] -Kthread file
             #include <synch.h>
             int rwlock_init(rwlock_t *rwlock, int type, void *arg);

          Parameters
             rwlock  pointer to reader-writer lock to be initialized

             type    USYNC_THREAD or USYNC_PROCESS

             arg     NULL (reserved for future use)

       DESCRIPTION
             rwlock_init initializes the reader-writer lock pointed to by
             rwlock to be of type type and in the unlocked state.  Once
             initialized, the lock can be used any number of times without
             being re-initialized.

          rwlock Parameter
             rwlock points to the reader-writer lock to be initialized.

          type Parameter
             type can be set to one of the following values:

             USYNC_THREAD    Initialize the reader-writer lock for threads
                             within the current process.

             USYNC_PROCESS   Initialize the reader-writer lock for threads
                             across processes.

          arg Parameter
             arg should be set to NULL.  It is not currently used, but is
             reserved for future use.

          Static Reader-Writer Initialization
             In this implementation, a reader-writer lock can be
             initialized statically if its storage is zero-filled.  In this
             case, the reader-writer lock is of type USYNC_THREAD, and
             rwlock_init need not be called.

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


                           Copyright 1994 Novell, Inc.               Page 1

      rwlock_init(3synch)                              rwlock_init(3synch)


         Errors
            If any of the following conditions is detected, the contents
            of rwlock are not changed, and rwlock_init returns the
            corresponding value:

            EINVAL   Invalid type argument specified.

      USAGE
         Warnings
            rwlock_init does not examine the rwlock argument before
            initializing it.  If rwlock_init is called more than once for
            the same reader-writer lock, it will overwrite its state.  It
            is the user's responsibility to ensure that rwlock_init is
            only called once for each reader-writer lock.

            Operations on locks initialized with rwlock_init are not
            recursive-a thread can deadlock if it attempts to reacquire a
            reader-writer lock that it already has acquired.

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

























                          Copyright 1994 Novell, Inc.               Page 2