123 lines
3.6 KiB
Groff
123 lines
3.6 KiB
Groff
|
.\" Copyright (c) 1998 Alex Nash
|
||
|
|
.\" 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.
|
||
|
|
.\"
|
||
|
|
.\" $Id$
|
||
|
|
.\"
|
||
|
|
.Dd August 4, 1998
|
||
|
|
.Dt PTHREAD_RWLOCK_RDLOCK 3
|
||
|
|
.Os
|
||
|
|
.Sh NAME
|
||
|
|
.Nm pthread_rwlock_rdlock ,
|
||
|
|
.Nm pthread_rwlock_tryrdlock
|
||
|
|
.Nd acquire a read/write lock for reading
|
||
|
|
.Sh SYNOPSIS
|
||
|
|
.Fd #include <pthread.h>
|
||
|
|
.Ft int
|
||
|
|
.Fn pthread_rwlock_rdlock "pthread_rwlock_t *lock"
|
||
|
|
.Ft int
|
||
|
|
.Fn pthread_rwlock_tryrdlock "pthread_rwlock_t *lock"
|
||
|
|
.Sh DESCRIPTION
|
||
|
|
The
|
||
|
|
.Fn pthread_rwlock_rdlock
|
||
|
|
function acquires a read lock on
|
||
|
|
.Fa lock
|
||
|
|
provided that
|
||
|
|
.Fa lock
|
||
|
|
is not presently held for writing and no writer threads are
|
||
|
|
presently blocked on the lock. If the read lock cannot be
|
||
|
|
immediately acquired, the calling thread blocks until it can
|
||
|
|
acquire the lock.
|
||
|
|
.Pp
|
||
|
|
The
|
||
|
|
.Fn pthread_rwlock_tryrdlock
|
||
|
|
function performs the same action, but does not block if the lock
|
||
|
|
cannot be immediately obtained (i.e. the lock is held for writing
|
||
|
|
or there are waiting writers).
|
||
|
|
.Pp
|
||
|
|
A thread may hold multiple concurrent read locks. If so,
|
||
|
|
.Fn pthread_rwlock_unlock
|
||
|
|
must be called once for each lock obtained.
|
||
|
|
.Pp
|
||
|
|
The results of acquiring a read lock while the calling thread holds
|
||
|
|
a write lock are undefined.
|
||
|
|
.Sh IMPLEMENTATION NOTES
|
||
|
|
To prevent writer starvation, writers are favored over readers.
|
||
|
|
.Sh RETURN VALUES
|
||
|
|
If successful, the
|
||
|
|
.Fn pthread_rwlock_rdlock
|
||
|
|
and
|
||
|
|
.Fn pthread_rwlock_tryrdlock
|
||
|
|
functions will return zero. Otherwise an error number will be returned
|
||
|
|
to indicate the error.
|
||
|
|
.Sh SEE ALSO
|
||
|
|
.Xr pthread_rwlock_init 3 ,
|
||
|
|
.Xr pthread_rwlock_trywrlock 3 ,
|
||
|
|
.Xr pthread_rwlock_unlock 3 ,
|
||
|
|
.Xr pthread_rwlock_wrlock 3
|
||
|
|
.Sh STANDARDS
|
||
|
|
The
|
||
|
|
.Fn pthread_rwlock_rdlock
|
||
|
|
and
|
||
|
|
.Fn pthread_rwlock_tryrdlock
|
||
|
|
functions are expected to conform to
|
||
|
|
.St -susv2 .
|
||
|
|
.Sh ERRORS
|
||
|
|
The
|
||
|
|
.Fn pthread_rwlock_tryrdlock
|
||
|
|
function will fail if:
|
||
|
|
.Bl -tag -width Er
|
||
|
|
.It Bq Er EBUSY
|
||
|
|
The lock could not be acquired because a writer holds the lock or
|
||
|
|
was blocked on it.
|
||
|
|
.El
|
||
|
|
.Pp
|
||
|
|
The
|
||
|
|
.Fn pthread_rwlock_rdlock
|
||
|
|
and
|
||
|
|
.Fn pthread_rwlock_tryrdlock
|
||
|
|
functions may fail if:
|
||
|
|
.Bl -tag -width Er
|
||
|
|
.It Bq Er EAGAIN
|
||
|
|
The lock could not be acquired because the maximum number of read locks
|
||
|
|
against
|
||
|
|
.Fa lock
|
||
|
|
has been exceeded.
|
||
|
|
.It Bq Er EDEADLK
|
||
|
|
The current thread already owns
|
||
|
|
.Fa lock
|
||
|
|
for writing.
|
||
|
|
.It Bq Er EINVAL
|
||
|
|
The value specified by
|
||
|
|
.Fa lock
|
||
|
|
is invalid.
|
||
|
|
.It Bq Er ENOMEM
|
||
|
|
Insufficient memory exists to initialize the lock (applies to
|
||
|
|
statically initialized locks only).
|
||
|
|
.El
|
||
|
|
.Sh HISTORY
|
||
|
|
The
|
||
|
|
.Fn pthread_rwlock_rdlock
|
||
|
|
function first appeared in
|
||
|
|
.Fx 3.0 .
|