165 lines
5.7 KiB
Groff
165 lines
5.7 KiB
Groff
.\" $NetBSD: pthread_rwlock_rdlock.3,v 1.9 2005/06/17 18:26:53 wiz Exp $
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.\"
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.\" Copyright (c) 2002 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" Copyright (c) 1998 Alex Nash
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD: src/lib/libpthread/man/pthread_rwlock_rdlock.3,v 1.5 2002/09/16 19:29:29 mini Exp $
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.\"
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.Dd January 30, 2003
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.Dt PTHREAD_RWLOCK_RDLOCK 3
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.Os
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.Sh NAME
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.Nm pthread_rwlock_rdlock ,
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.Nm pthread_rwlock_timedrdlock ,
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.Nm pthread_rwlock_tryrdlock
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.Nd acquire a read/write lock for reading
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.Sh LIBRARY
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.Lb libpthread
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.Sh SYNOPSIS
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.In pthread.h
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.Ft int
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.Fn pthread_rwlock_rdlock "pthread_rwlock_t *lock"
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.Ft int
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.Fn pthread_rwlock_timedrdlock "pthread_rwlock_t * restrict lock" "const struct timespec * restrict abstime"
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.Ft int
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.Fn pthread_rwlock_tryrdlock "pthread_rwlock_t *lock"
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.Sh DESCRIPTION
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The
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.Fn pthread_rwlock_rdlock
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function acquires a read lock on
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.Fa lock
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provided that
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.Fa lock
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is not presently held for writing and no writer threads are
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presently blocked on the lock.
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If the read lock cannot be immediately acquired, the calling thread
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blocks until it can acquire the lock.
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.Pp
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The
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.Fn pthread_rwlock_timedrdlock
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performs the same action, but will not wait beyond
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.Fa abstime
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to obtain the lock before returning.
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.Pp
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The
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.Fn pthread_rwlock_tryrdlock
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function performs the same action as
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.Fn pthread_rwlock_rdlock ,
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but does not block if the lock cannot be immediately obtained (i.e.,
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the lock is held for writing or there are waiting writers).
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.Pp
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A thread may hold multiple concurrent read locks.
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If so,
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.Fn pthread_rwlock_unlock
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must be called once for each lock obtained.
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.Pp
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The results of acquiring a read lock while the calling thread holds
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a write lock are undefined.
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.Sh RETURN VALUES
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If successful, the
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.Fn pthread_rwlock_rdlock ,
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.Fn pthread_rwlock_timedrdlock ,
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and
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.Fn pthread_rwlock_tryrdlock
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functions will return zero.
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Otherwise an error number will be returned to indicate the error.
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.Sh ERRORS
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The
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.Fn pthread_rwlock_tryrdlock
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function shall fail if:
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.Bl -tag -width Er
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.It Bq Er EBUSY
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The lock could not be acquired because a writer holds the lock or
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was blocked on it.
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.El
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.Pp
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The
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.Fn pthread_rwlock_timedrdlock
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function shall fail if:
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.Bl -tag -width Er
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.It Bq Er ETIMEDOUT
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The time specified by
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.Fa abstime
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was reached before the lock could be obtained.
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.El
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.Pp
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The
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.Fn pthread_rwlock_rdlock ,
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.Fn pthread_rwlock_timedrdlock ,
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and
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.Fn pthread_rwlock_tryrdlock
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functions may fail if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The lock could not be acquired because the maximum number of read locks
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against
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.Fa lock
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has been exceeded.
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.It Bq Er EDEADLK
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The current thread already owns
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.Fa lock
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for writing.
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.It Bq Er EINVAL
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The value specified by
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.Fa lock
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is invalid.
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.El
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.Sh SEE ALSO
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.Xr pthread_rwlock_destroy 3 ,
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.Xr pthread_rwlock_init 3 ,
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.Xr pthread_rwlock_unlock 3 ,
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.Xr pthread_rwlock_wrlock 3
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.Sh STANDARDS
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.Fn pthread_rwlock_rdlock ,
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.Fn pthread_rwlock_timedrdlock ,
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and
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.Fn pthread_rwlock_tryrdlock
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conform to
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.St -p1003.1-96 .
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