PTHREAD_RWLOCK_TRYWRLOCK(3P)				     POSIX Programmer's Manual				      PTHREAD_RWLOCK_TRYWRLOCK(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

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 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(3P)