1.\" $NetBSD: RUN_ONCE.9,v 1.8 2010/07/06 22:29:29 jruoho Exp $ 2.\" 3.\" Copyright (c)2005 YAMAMOTO Takashi, 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25.\" SUCH DAMAGE. 26.\" 27.\" ------------------------------------------------------------ 28.Dd July 7, 2010 29.Dt RUN_ONCE 9 30.Os 31.\" ------------------------------------------------------------ 32.Sh NAME 33.Nm RUN_ONCE 34.Nd Run a function exactly once 35.\" ------------------------------------------------------------ 36.Sh SYNOPSIS 37.In sys/once.h 38.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 39.Vt ONCE_DECL(control); 40.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 41.Ft int 42.Fn RUN_ONCE \ 43"once_t *control" "int (*init_func)(void)" 44.\" ------------------------------------------------------------ 45.Sh DESCRIPTION 46.Fn RUN_ONCE 47provides a functionality similar to 48.Xr pthread_once 3 . 49It ensures that, for a given 50.Fa control , 51.Fn init_func 52is executed (successfully) exactly once. 53It is considered as a successful execution if and only if 54.Fn init_func 55returned 0. 56As long as there was no successful execution, 57.Fn RUN_ONCE 58will try again each time it is called. 59.Pp 60.Fn RUN_ONCE 61can sleep if it's called concurrently. 62.\" ------------------------------------------------------------ 63.Sh RETURN VALUES 64On failure, 65.Fn RUN_ONCE 66returns what 67.Fn init_func 68returned. 69Otherwise, it returns 0. 70.\" ------------------------------------------------------------ 71.Sh EXAMPLES 72The following example shows how 73.Fn RUN_ONCE 74is used. 75Regardless of how many times 76.Fn some_func 77is executed, 78.Fn init_func 79will be executed exactly once. 80.Bd -literal 81static int 82init_func(void) 83{ 84 85 /* 86 * do some initialization. 87 */ 88 89 return 0; /* success */ 90} 91 92int 93some_func(void) 94{ 95 static ONCE_DECL(control); 96 97 RUN_ONCE(\*[Am]control, init_func); 98 99 /* 100 * we are sure that init_func has already been completed here. 101 */ 102} 103.Ed 104.\" ------------------------------------------------------------ 105.Sh SEE ALSO 106.Xr pthread_once 3 , 107.Xr condvar 9 , 108.Xr intro 9 109