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 January 16, 2004 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.Lb libthr 36.Sh SYNOPSIS 37.In pthread.h 38.Ft int 39.Fn pthread_rwlock_timedrdlock "pthread_rwlock_t *rwlock" "const struct timespec *abs_timeout" 40.Sh DESCRIPTION 41This function acquires a read lock on the read-write lock 42.Fa rwlock . 43However, if the lock cannot be 44acquired without waiting for another thread to 45unlock the lock, 46this wait shall be terminated when 47.Fa abs_timeout 48expires. 49.Pp 50A thread may hold multiple concurrent read locks. 51The 52.Xr pthread_rwlock_unlock 3 53function must be called once for each lock acquired. 54.Pp 55If the thread should be interrupted by a signal, 56the 57.Fn pthread_rwlock_timedrdlock 58function will be automatically restarted after the thread returns from 59the signal handler. 60.Pp 61The calling thread may deadlock if 62at the time the call is made it holds a write lock on 63.Fa rwlock . 64The results are undefined if this function is called with 65an uninitialized read-write lock. 66.Sh IMPLEMENTATION NOTES 67To prevent writer starvation, writers are favored over readers. 68.Sh RETURN VALUES 69If successful, the 70.Fn pthread_rwlock_timedrdlock 71function will return zero. 72Otherwise, an error number will be returned to indicate the error. 73.Pp 74This function shall not return an error code of 75.Er EINTR . 76.Sh ERRORS 77The 78.Fn pthread_rwlock_timedrdlock 79function will fail if: 80.Bl -tag -width Er 81.It Bq Er ETIMEDOUT 82The lock could not be acquired before the specified timeout expired. 83.El 84.Pp 85The 86.Fn pthread_rwlock_timedrdlock 87function may fail if: 88.Bl -tag -width Er 89.It Bq Er EAGAIN 90The read lock could not be 91acquired because the maximum number of read locks for 92.Fa rwlock 93would be exceeded. 94.It Bq Er EDEADLK 95The calling thread already holds a write lock on 96.Fa rwlock . 97.It Bq Er EINVAL 98The value specified by 99.Fa rwlock 100does not refer to an initialized read-write lock object, 101or the 102.Fa abs_timeout 103nanosecond value is less than zero or 104greater than or equal to 1 billion. 105.El 106.Sh SEE ALSO 107.Xr pthread_rwlock_init 3 , 108.Xr pthread_rwlock_timedwrlock 3 , 109.Xr pthread_rwlock_unlock 3 110.Sh STANDARDS 111The 112.Fn pthread_rwlock_timedrdlock 113function is expected to conform to 114.St -p1003.1-96 . 115.Sh HISTORY 116The 117.Fn pthread_rwlock_timedrdlock 118function first appeared in 119.Fx 5.2 . 120