NAME

       pthread_rwlock_destroy,  pthread_rwlock_init  -  destroy  and initialize a read-write lock
       object

SYNOPSIS

       #include <pthread.h>

       int pthread_rwlock_destroy(pthread_rwlock_t *rwlock);
       int pthread_rwlock_init(pthread_rwlock_t *restrict rwlock,
              const pthread_rwlockattr_t *restrict attr);

DESCRIPTION

       The pthread_rwlock_destroy() function shall destroy the read-write lock object  referenced
       by  rwlock and release any resources used by the lock. The effect of subsequent use of the
       lock   is   undefined   until   the   lock   is   reinitialized   by   another   call   to
       pthread_rwlock_init().  An  implementation  may  cause pthread_rwlock_destroy() to set the
       object  referenced  by  rwlock  to  an   invalid   value.   Results   are   undefined   if
       pthread_rwlock_destroy()  is called when any thread holds rwlock. Attempting to destroy an
       uninitialized read-write lock results in undefined behavior.

       The pthread_rwlock_init() function shall allocate any resources required to use the  read-
       write  lock  referenced  by  rwlock  and  initializes  the  lock to an unlocked state with
       attributes referenced by attr. If attr is NULL, the  default  read-write  lock  attributes
       shall  be used; the effect is the same as passing the address of a default read-write lock
       attributes object. Once initialized, the lock can be used  any  number  of  times  without
       being  reinitialized.  Results are undefined if pthread_rwlock_init() is called specifying
       an already initialized read-write lock. Results are undefined if a read-write lock is used
       without first being initialized.

       If  the  pthread_rwlock_init()  function  fails,  rwlock  shall not be initialized and the
       contents of rwlock are undefined.

       Only the object referenced by rwlock may  be  used  for  performing  synchronization.  The
       result  of  referring  to  copies  of  that  object  in calls to pthread_rwlock_destroy(),
       pthread_rwlock_rdlock(),    pthread_rwlock_timedrdlock(),    pthread_rwlock_timedwrlock(),
       pthread_rwlock_tryrdlock(),    pthread_rwlock_trywrlock(),   pthread_rwlock_unlock(),   or
       pthread_rwlock_wrlock() is undefined.

RETURN VALUE

       If successful, the  pthread_rwlock_destroy()  and  pthread_rwlock_init()  functions  shall
       return zero; otherwise, an error number shall be returned to indicate the error.

       The  [EBUSY]  and  [EINVAL]  error  checks,  if implemented, act as if they were performed
       immediately at the beginning of processing for the function and  caused  an  error  return
       prior to modifying the state of the read-write lock specified by rwlock.

ERRORS

       The pthread_rwlock_destroy() function may fail if:

       EBUSY  The  implementation  has  detected  an  attempt to destroy the object referenced by
              rwlock while it is locked.

       EINVAL The value specified by rwlock is invalid.

       The pthread_rwlock_init() function shall fail if:

       EAGAIN The system lacked the necessary resources (other than memory) to initialize another
              read-write lock.

       ENOMEM Insufficient memory exists to initialize the read-write lock.

       EPERM  The caller does not have the privilege to perform the operation.

       The pthread_rwlock_init() function may fail if:

       EBUSY  The implementation has detected an attempt to reinitialize the object referenced by
              rwlock, a previously initialized but not yet destroyed read-write lock.

       EINVAL The value specified by attr is invalid.

       These functions shall not return an error code of [EINTR].

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       Applications using these and related read-write lock functions may be subject to  priority
       inversion,  as  discussed  in the Base Definitions volume of IEEE Std 1003.1-2001, Section
       3.285, Priority Inversion.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       pthread_rwlock_rdlock() , pthread_rwlock_timedrdlock()  ,  pthread_rwlock_timedwrlock()  ,
       pthread_rwlock_tryrdlock()   ,   pthread_rwlock_trywrlock()  ,  pthread_rwlock_unlock()  ,
       pthread_rwlock_wrlock() , the Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2003  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .