NAME

       pthread_rwlock_trywrlock, pthread_rwlock_wrlock - lock a read-write 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 function 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 starvation.

       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.

       The pthread_rwlock_wrlock() function may fail if:

       EDEADLK
              The current thread already owns the read-write lock for writing or reading.

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

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       Applications using these 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_destroy()      ,      pthread_rwlock_rdlock()     ,     pthread_rwlock_timedrdlock()     ,
       pthread_rwlock_timedwrlock()  ,  pthread_rwlock_tryrdlock()  ,   pthread_rwlock_unlock()   ,   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 .