1.\" Copyright (c) 1998 Alex Nash 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.Dd August 4, 1998 26.Dt PTHREAD_RWLOCK_WRLOCK 3 27.Os 28.Sh NAME 29.Nm pthread_rwlock_wrlock , 30.Nm pthread_rwlock_trywrlock 31.Nd acquire a read/write lock for writing 32.Sh LIBRARY 33.Lb libpthread 34.Sh SYNOPSIS 35.In pthread.h 36.Ft int 37.Fn pthread_rwlock_wrlock "pthread_rwlock_t *lock" 38.Ft int 39.Fn pthread_rwlock_trywrlock "pthread_rwlock_t *lock" 40.Sh DESCRIPTION 41The 42.Fn pthread_rwlock_wrlock 43function blocks until a write lock can be acquired against 44.Fa lock . 45The 46.Fn pthread_rwlock_trywrlock 47function performs the same action, but does not block if the lock 48cannot be immediately obtained. 49.Pp 50The results are undefined if the calling thread already holds the 51lock at the time the call is made. 52.Sh IMPLEMENTATION NOTES 53To prevent writer starvation, writers are favored over readers. 54.Sh RETURN VALUES 55If successful, the 56.Fn pthread_rwlock_wrlock 57and 58.Fn pthread_rwlock_trywrlock 59functions will return zero. 60Otherwise an error number will be returned 61to indicate the error. 62.Sh ERRORS 63The 64.Fn pthread_rwlock_trywrlock 65function will fail if: 66.Bl -tag -width Er 67.It Bq Er EBUSY 68The calling thread is not able to acquire the lock without blocking. 69.El 70.Pp 71The 72.Fn pthread_rwlock_wrlock 73and 74.Fn pthread_rwlock_trywrlock 75functions may fail if: 76.Bl -tag -width Er 77.It Bq Er EDEADLK 78The calling thread already owns the read/write lock (for reading 79or writing). 80.It Bq Er EINVAL 81The value specified by 82.Fa lock 83is invalid. 84.It Bq Er ENOMEM 85Insufficient memory exists to initialize the lock (applies to 86statically initialized locks only). 87.El 88.Sh SEE ALSO 89.Xr pthread_rwlock_init 3 , 90.Xr pthread_rwlock_rdlock 3 , 91.Xr pthread_rwlock_tryrdlock 3 , 92.Xr pthread_rwlock_unlock 3 93.Sh STANDARDS 94The 95.Fn pthread_rwlock_wrlock 96and 97.Fn pthread_rwlock_trywrlock 98functions are expected to conform to 99.St -susv2 . 100.Sh HISTORY 101The 102.Fn pthread_rwlock_wrlock 103function first appeared in 104.Fx 3.0 . 105