356 lines
10 KiB
Groff
356 lines
10 KiB
Groff
.\" $NetBSD: pthread_rwlock.3,v 1.7 2017/10/22 16:37:24 abhinav Exp $
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.\"
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.\" Copyright (c) 2002, 2010 The NetBSD Foundation, Inc.
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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 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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.\" ----------------------------------------------------------------------------
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.Dd July 8, 2010
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.Dt PTHREAD_RWLOCK 3
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.Os
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.Sh NAME
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.Nm pthread_rwlock ,
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.Nm pthread_rwlock_init ,
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.Nm pthread_rwlock_destroy ,
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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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.Nm pthread_rwlock_wrlock ,
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.Nm pthread_rwlock_timedwrlock ,
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.Nm pthread_rwlock_trywrlock ,
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.Nm pthread_rwlock_unlock
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.Nd read/write lock interface
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.Sh LIBRARY
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.Lb libpthread
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.\" ----------------------------------------------------------------------------
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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_init "pthread_rwlock_t * restrict lock" \
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"const pthread_rwlockattr_t * restrict attr"
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.Vt pthread_rwlock_t lock No = Dv PTHREAD_RWLOCK_INITIALIZER ;
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.Ft int
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.Fn pthread_rwlock_destroy "pthread_rwlock_t *lock"
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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" \
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"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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.Ft int
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.Fn pthread_rwlock_wrlock "pthread_rwlock_t *lock"
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.Ft int
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.Fn pthread_rwlock_timedwrlock "pthread_rwlock_t * restrict lock" \
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"const struct timespec * restrict abstime"
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.Ft int
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.Fn pthread_rwlock_trywrlock "pthread_rwlock_t *lock"
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.Ft int
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.Fn pthread_rwlock_unlock "pthread_rwlock_t *lock"
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.\" ----------------------------------------------------------------------------
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.Sh DESCRIPTION
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The
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.Fn pthread_rwlock_init
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function is used to initialize a read/write lock, with attributes
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specified by
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.Fa attr .
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If
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.Fa attr
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is
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.Dv NULL ,
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the default read/write lock attributes are used.
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.Pp
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The results of calling
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.Fn pthread_rwlock_init
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with an already initialized lock are undefined.
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.Pp
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The macro
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.Dv PTHREAD_RWLOCK_INITIALIZER
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can be used to initialize a read/write lock when the allocation can be done
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statically, no error checking is required, and the default attributes are
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appropriate.
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The behavior is similar to calling
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.Fn pthread_rwlock_init
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with
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.Fa attr
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specified as
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.Dv NULL .
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.Pp
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.\" -----
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The
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.Fn pthread_rwlock_destroy
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function is used to destroy a read/write lock previously created with
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.Fn pthread_rwlock_init .
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.Pp
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.\" -----
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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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.Pp
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.\" -----
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The
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.Fn pthread_rwlock_wrlock
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function blocks until a write lock can be acquired against
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.Fa lock .
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.Pp
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The
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.Fn pthread_rwlock_timedwrlock
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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_trywrlock
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function performs the same action as
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.Fn pthread_rwlock_wrlock ,
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but does not block if the lock cannot be immediately obtained.
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.Pp
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The results are undefined if the calling thread already holds the
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lock at the time the call is made.
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.Pp
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.\" -----
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The
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.Fn pthread_rwlock_unlock
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function is used to release the read/write lock previously obtained by
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.Fn pthread_rwlock_rdlock ,
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.Fn pthread_rwlock_wrlock ,
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.Fn pthread_rwlock_tryrdlock ,
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or
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.Fn pthread_rwlock_trywrlock .
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.\" ----------------------------------------------------------------------------
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.Sh RETURN VALUES
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If successful, the
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.Fn pthread_rwlock_init
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function will return zero.
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Otherwise an error number will be returned to indicate the error.
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.Pp
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If successful, the
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.Fn pthread_rwlock_destroy ,
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.Fn pthread_rwlock_rdlock ,
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.Fn pthread_rwlock_timedrdlock ,
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.Fn pthread_rwlock_tryrdlock ,
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.Fn pthread_rwlock_wrlock ,
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.Fn pthread_rwlock_timedwrlock ,
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.Fn pthread_rwlock_trywrlock ,
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and
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.Fn pthread_rwlock_unlock
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will return zero.
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Otherwise an error number will be returned to indicate the error.
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.Pp
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The results are undefined if
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.Fa lock
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is not held by the calling thread.
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.\" ----------------------------------------------------------------------------
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.Sh ERRORS
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The
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.Fn pthread_rwlock_init
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function may fail if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The system lacks the resources to initialize another read-write lock.
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.It Bq Er EBUSY
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The system has detected an attempt to re-initialize the object
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referenced by
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.Fa lock ,
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a previously initialized but not yet destroyed read/write lock.
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.It Bq Er EINVAL
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The value specified by
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.Fa attr
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is invalid.
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.It Bq Er ENOMEM
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Insufficient memory exists to initialize the read-write lock.
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.El
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.Pp
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.\" -----
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The
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.Fn pthread_rwlock_destroy
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function may fail if:
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.Bl -tag -width Er
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.It Bq Er EBUSY
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The system has detected an attempt to destroy the object referenced by
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.Fa lock
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while it is locked.
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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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.Pp
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.\" -----
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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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.Pp
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.\" -----
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The
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.Fn pthread_rwlock_trywrlock
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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 calling thread is not able to acquire the lock without blocking.
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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_wrlock ,
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.Fn pthread_rwlock_timedwrlock ,
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and
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.Fn pthread_rwlock_trywrlock
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functions may fail if:
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.Bl -tag -width Er
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.It Bq Er EDEADLK
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The calling thread already owns the read/write lock (for reading
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or 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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.Pp
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.\" -----
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The
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.Fn pthread_rwlock_unlock
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function may fail if:
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.Bl -tag -width Er
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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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.It Bq Er EPERM
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The current thread does not own the read/write lock.
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.El
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.\" ----------------------------------------------------------------------------
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.Sh SEE ALSO
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.Xr pthread 3 ,
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.Xr pthread_barrier 3 ,
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.Xr pthread_cond 3 ,
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.Xr pthread_mutex 3 ,
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.Xr pthread_rwlockattr 3 ,
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.Xr pthread_spin 3
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.Sh STANDARDS
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These functions conform to
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.St -p1003.1-2001 .
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.\" ----------------------------------------------------------------------------
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.Sh BUGS
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The
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.Dv PTHREAD_PROCESS_SHARED
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attribute is not supported.
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