freebsd-dev/share/man/man3/pthread_rwlock_timedrdlock.3

.\" Copyright (c) 2004 Michael Telahun Makonnen
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd August 17, 2018
.Dt PTHREAD_RWLOCK_TIMEDRDLOCK 3
.Os
.Sh NAME
.Nm pthread_rwlock_timedrdlock
.Nd "acquire a read-write lock for reading or give up after a specified period"
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fn pthread_rwlock_timedrdlock "pthread_rwlock_t *restrict rwlock" "const struct timespec *restrict abs_timeout"
.Sh DESCRIPTION
This function acquires a read lock on the read-write lock
.Fa rwlock .
However, if the lock cannot be
acquired without waiting for another thread to
unlock the lock,
this wait shall be terminated when
.Fa abs_timeout
expires.
.Pp
A thread may hold multiple concurrent read locks.
The
.Xr pthread_rwlock_unlock 3
function must be called once for each lock acquired.
.Pp
If the thread should be interrupted by a signal,
the
.Fn pthread_rwlock_timedrdlock
function will be automatically restarted after the thread returns from
the signal handler.
.Pp
The calling thread may deadlock if
at the time the call is made it holds a write lock on
.Fa rwlock .
The results are undefined if this function is called with
an uninitialized read-write lock.
.Sh IMPLEMENTATION NOTES
To prevent writer starvation, writers are favored over readers.
.Sh RETURN VALUES
If successful, the
.Fn pthread_rwlock_timedrdlock
function will return zero.
Otherwise, an error number will be returned to indicate the error.
.Pp
This function shall not return an error code of
.Er EINTR .
.Sh ERRORS
The
.Fn pthread_rwlock_timedrdlock
function will fail if:
.Bl -tag -width Er
.It Bq Er ETIMEDOUT
The lock could not be acquired before the specified timeout expired.
.El
.Pp
The
.Fn pthread_rwlock_timedrdlock
function may fail if:
.Bl -tag -width Er
.It Bq Er EAGAIN
The read lock could not be
acquired because the maximum number of read locks for
.Fa rwlock
would be exceeded.
.It Bq Er EDEADLK
The calling thread already holds a write lock on
.Fa rwlock .
.It Bq Er EINVAL
The value specified by
.Fa rwlock
does not refer to an initialized read-write lock object,
or the
.Fa abs_timeout
nanosecond value is less than zero or
greater than or equal to 1 billion.
.El
.Sh SEE ALSO
.Xr pthread_rwlock_init 3 ,
.Xr pthread_rwlock_timedwrlock 3 ,
.Xr pthread_rwlock_unlock 3
.Sh STANDARDS
The
.Fn pthread_rwlock_timedrdlock
function is expected to conform to
.St -p1003.1-96 .
.Sh HISTORY
The
.Fn pthread_rwlock_timedrdlock
function first appeared in
.Fx 5.2 .