1.\" Copyright (c) 2004 Michael Telahun Makonnen 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.\" $FreeBSD$ 26.\" 27.Dd August 17, 2018 28.Dt PTHREAD_RWLOCK_TIMEDRDLOCK 3 29.Os 30.Sh NAME 31.Nm pthread_rwlock_timedrdlock 32.Nd "acquire a read-write lock for reading or give up after a specified period" 33.Sh LIBRARY 34.Lb libpthread 35.Sh SYNOPSIS 36.In pthread.h 37.Ft int 38.Fn pthread_rwlock_timedrdlock "pthread_rwlock_t *restrict rwlock" "const struct timespec *restrict abs_timeout" 39.Sh DESCRIPTION 40This function acquires a read lock on the read-write lock 41.Fa rwlock . 42However, if the lock cannot be 43acquired without waiting for another thread to 44unlock the lock, 45this wait shall be terminated when 46.Fa abs_timeout 47expires. 48.Pp 49A thread may hold multiple concurrent read locks. 50The 51.Xr pthread_rwlock_unlock 3 52function must be called once for each lock acquired. 53.Pp 54If the thread should be interrupted by a signal, 55the 56.Fn pthread_rwlock_timedrdlock 57function will be automatically restarted after the thread returns from 58the signal handler. 59.Pp 60The calling thread may deadlock if 61at the time the call is made it holds a write lock on 62.Fa rwlock . 63The results are undefined if this function is called with 64an uninitialized read-write lock. 65.Sh IMPLEMENTATION NOTES 66To prevent writer starvation, writers are favored over readers. 67.Sh RETURN VALUES 68If successful, the 69.Fn pthread_rwlock_timedrdlock 70function will return zero. 71Otherwise, an error number will be returned to indicate the error. 72.Pp 73This function shall not return an error code of 74.Er EINTR . 75.Sh ERRORS 76The 77.Fn pthread_rwlock_timedrdlock 78function will fail if: 79.Bl -tag -width Er 80.It Bq Er ETIMEDOUT 81The lock could not be acquired before the specified timeout expired. 82.El 83.Pp 84The 85.Fn pthread_rwlock_timedrdlock 86function may fail if: 87.Bl -tag -width Er 88.It Bq Er EAGAIN 89The read lock could not be 90acquired because the maximum number of read locks for 91.Fa rwlock 92would be exceeded. 93.It Bq Er EDEADLK 94The calling thread already holds a write lock on 95.Fa rwlock . 96.It Bq Er EINVAL 97The value specified by 98.Fa rwlock 99does not refer to an initialized read-write lock object, 100or the 101.Fa abs_timeout 102nanosecond value is less than zero or 103greater than or equal to 1 billion. 104.El 105.Sh SEE ALSO 106.Xr pthread_rwlock_init 3 , 107.Xr pthread_rwlock_timedwrlock 3 , 108.Xr pthread_rwlock_unlock 3 109.Sh STANDARDS 110The 111.Fn pthread_rwlock_timedrdlock 112function is expected to conform to 113.St -p1003.1-96 . 114.Sh HISTORY 115The 116.Fn pthread_rwlock_timedrdlock 117function first appeared in 118.Fx 5.2 . 119