pthread_rwlock_wrlock

       lock object for writing

SYNOPSIS
       #include <pthread.h>

       int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);
       int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);


DESCRIPTION
       The pthread_rwlock_trywrlock() function shall apply a write  lock  like
       the pthread_rwlock_wrlock() function, with the exception that the func-
       tion shall fail if any thread currently holds rwlock  (for  reading  or
       writing).

       The  pthread_rwlock_wrlock()  function  shall apply a write lock to the
       read-write lock referenced by rwlock. The calling thread  acquires  the
       write  lock  if no other thread (reader or writer) holds the read-write
       lock rwlock. Otherwise, the thread shall block until it can acquire the
       lock.  The  calling thread may deadlock if at the time the call is made
       it holds the read-write lock (whether a read or write lock).

       Implementations may favor writers over readers to avoid writer  starva-
       tion.

       Results  are  undefined  if  any  of these functions are called with an
       uninitialized read-write lock.

       If a signal is delivered to a thread waiting for a read-write lock  for
       writing, upon return from the signal handler the thread resumes waiting
       for the read-write lock for writing as if it was not interrupted.

RETURN VALUE
       The pthread_rwlock_trywrlock() function shall return zero if  the  lock
       for  writing  on  the  read-write  lock  object referenced by rwlock is
       acquired. Otherwise, an error number shall be returned to indicate  the
       error.

       If  successful, the pthread_rwlock_wrlock() function shall return zero;
       otherwise, an error number shall be returned to indicate the error.

ERRORS
       The pthread_rwlock_trywrlock() function shall fail if:

       EBUSY  The read-write lock could not be acquired for writing because it
              was already locked for reading or writing.


       The  pthread_rwlock_trywrlock()  and  pthread_rwlock_wrlock() functions
       may fail if:

       EINVAL The value specified by rwlock does not refer to  an  initialized
              read-write lock object.

EXAMPLES
       None.

APPLICATION USAGE
       Applications using these functions may be subject  to  priority  inver-
       sion,    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_destroy()       ,       pthread_rwlock_rdlock()        ,
       pthread_rwlock_timedrdlock()     ,    pthread_rwlock_timedwrlock()    ,
       pthread_rwlock_tryrdlock() , pthread_rwlock_unlock() , the Base Defini-
       tions 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 .



IEEE/The Open Group                  2003          PTHREAD_RWLOCK_TRYWRLOCK(P)