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120 lines
3.7 KiB
Groff
120 lines
3.7 KiB
Groff
.\" Copyright (c) 2004 Michael Telahun Makonnen
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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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.\" $FreeBSD$
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.\"
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.Dd January 16, 2004
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.Dt PTHREAD_RWLOCK_TIMEDRDLOCK 3
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.Os
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.Sh NAME
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.Nm pthread_rwlock_timedrdlock
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.Nd "acquire a read-write lock for reading or give up after a specified period"
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.Sh LIBRARY
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.Lb libpthread
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.Lb libthr
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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_timedrdlock "pthread_rwlock_t *rwlock" "const struct timespec *abs_timeout"
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.Sh DESCRIPTION
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This function acquires a read lock on the read-write lock
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.Fa rwlock .
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However, if the lock cannot be
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acquired without waiting for another thread to
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unlock the lock,
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this wait shall be terminated when
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.Fa abs_timeout
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expires.
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.Pp
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A thread may hold multiple concurrent read locks.
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The
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.Xr pthread_rwlock_unlock 3
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function must be called once for each lock acquired.
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.Pp
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If the thread should be interrupted by a signal,
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the
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.Fn pthread_rwlock_timedrdlock
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function will be automatically restarted after the thread returns from
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the signal handler.
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.Pp
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The calling thread may deadlock if
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at the time the call is made it holds a write lock on
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.Fa rwlock .
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The results are undefined if this function is called with
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an uninitialized read-write lock.
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.Sh IMPLEMENTATION NOTES
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To prevent writer starvation, writers are favored over readers.
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.Sh RETURN VALUES
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If successful, the
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.Fn pthread_rwlock_timedrdlock
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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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This function shall not return an error code of
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.Er EINTR .
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.Sh ERRORS
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The
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.Fn pthread_rwlock_timedrdlock
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function will fail if:
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.Bl -tag -width Er
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.It Bq Er ETIMEDOUT
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The lock could not be acquired before the specified timeout expired.
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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 may fail if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The read lock could not be
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acquired because the maximum number of read locks for
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.Fa rwlock
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would be exceeded.
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.It Bq Er EDEADLK
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The calling thread already holds a write lock on
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.Fa rwlock .
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.It Bq Er EINVAL
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The value specified by
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.Fa rwlock
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does not refer to an initialized read-write lock object,
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or the
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.Fa abs_timeout
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nanosecond value is less than zero or
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greater than or equal to 1 billion.
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.El
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.Sh SEE ALSO
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.Xr pthread_rwlock_init 3 ,
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.Xr pthread_rwlock_timedwrlock 3 ,
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.Xr pthread_rwlock_unlock 3
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.Sh STANDARDS
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The
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.Fn pthread_rwlock_timedrdlock
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function is expected to conform to
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.St -p1003.1-96 .
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.Sh HISTORY
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The
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.Fn pthread_rwlock_timedrdlock
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function first appeared in
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.Fx 5.2 .
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