NAME    [Toc]    [Back]

     pthread_rwlock_wrlock, pthread_rwlock_trywrlock - acquire  a
read/write
     lock for writing

SYNOPSIS    [Toc]    [Back]

     #include <pthread.h>

     int
     pthread_rwlock_wrlock(pthread_rwlock_t *lock);

     int
     pthread_rwlock_trywrlock(pthread_rwlock_t *lock);

DESCRIPTION    [Toc]    [Back]

     The  pthread_rwlock_wrlock()  function  blocks until a write
lock can be acquired
 against lock.  The  pthread_rwlock_trywrlock()  function performs
     the  same  action,  but does not block if the lock cannot be
immediately obtained.


     The results are undefined  if  the  calling  thread  already
holds the lock at
     the time the call is made.

IMPLEMENTATION NOTES    [Toc]    [Back]

     To prevent writer starvation, writers are favored over readers.

RETURN VALUES    [Toc]    [Back]

     If    successful,    the     pthread_rwlock_wrlock()     and
pthread_rwlock_trywrlock()
     functions  will return zero.  Otherwise an error number will
be returned
     to indicate the error.

ERRORS    [Toc]    [Back]

     The pthread_rwlock_trywrlock() function will fail if:

     [EBUSY]       The calling thread is not able to acquire  the
lock without
                   blocking.

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

     [EDEADLK]     The calling thread already owns the read/write
lock (for
                   reading or writing).

     [EINVAL]      The value specified by lock is invalid.

     [ENOMEM]       Insufficient  memory exists to initialize the
lock (applies
                   to statically initialized locks only).

SEE ALSO    [Toc]    [Back]

     pthread_rwlock_unlock(3)

STANDARDS    [Toc]    [Back]

     The pthread_rwlock_wrlock()  and  pthread_rwlock_trywrlock()
functions are
     expected to conform to Version 2 of the Single UNIX Specification.

HISTORY    [Toc]    [Back]

     The  pthread_rwlock_wrlock()  function  first  appeared   in
FreeBSD 3.0 and
     OpenBSD 2.5.

OpenBSD      3.6                          August      4,     1998