PTHREAD_RWLOCK_TRYWRLOCK(P)				     POSIX Programmer's Manual				       PTHREAD_RWLOCK_TRYWRLOCK(P)

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_tryrd-
       lock() , 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 Technol-
       ogy -- 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)