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 (con-
       sult the corresponding 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  refer-
       enced 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, Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                  PTHREAD_RWLOCK_TRYWRLOCK(3P)