109 lines
3.2 KiB
Groff
109 lines
3.2 KiB
Groff
.\" $NetBSD: RUN_ONCE.9,v 1.5 2006/01/17 00:14:16 wiz Exp $
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.\"
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.\" Copyright (c)2005 YAMAMOTO Takashi,
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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 January 17, 2006
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.Dt RUN_ONCE 9
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.Os
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.\" ------------------------------------------------------------
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.Sh NAME
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.Nm RUN_ONCE
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.Nd Run a function exactly once
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.\" ------------------------------------------------------------
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.Sh SYNOPSIS
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.In sys/once.h
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Vt ONCE_DECL(control);
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Ft int
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.Fn RUN_ONCE \
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"once_t *control" "int (*init_func)(void)"
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.\" ------------------------------------------------------------
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.Sh DESCRIPTION
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.Fn RUN_ONCE
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provides a functionality similar to
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.Fn pthread_once 3 .
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It ensures that, for a given
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.Fa control ,
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.Fn init_func
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is executed (successfully) exactly once.
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It is considered as a successful execution if and only if
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.Fn init_func
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returned 0.
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As long as there was no successful execution,
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.Fn RUN_ONCE
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will try again each time it is called.
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.Pp
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.Fn RUN_ONCE
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can sleep if it's called concurrently.
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.\" ------------------------------------------------------------
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.Sh RETURN VALUES
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On failure,
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.Fn RUN_ONCE
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returns what
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.Fn init_func
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returned.
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Otherwise, it returns 0.
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.\" ------------------------------------------------------------
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.Sh EXAMPLES
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The following example shows how
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.Fn RUN_ONCE
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is used.
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Regardless of how many times
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.Fn some_func
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is executed,
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.Fn init_func
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will be executed exactly once.
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.Bd -literal
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static int
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init_func(void)
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{
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/*
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* do some initialization.
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*/
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return 0; /* success */
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}
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int
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some_func(void)
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{
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static DECL_ONCE(control);
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RUN_ONCE(\*[Am]control, init_func);
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/*
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* we are sure that init_func has already been completed here.
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*/
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}
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.Ed
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.\" ------------------------------------------------------------
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.Sh SEE ALSO
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.Xr pthread_once 3 ,
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.Xr intro 9 ,
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.Xr ltsleep 9
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