1.\" $NetBSD: RUN_ONCE.9,v 1.11 2019/03/19 10:17:35 wiz 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 March 19, 2019 29.Dt RUN_ONCE 9 30.Os 31.\" ------------------------------------------------------------ 32.Sh NAME 33.Nm RUN_ONCE , 34.Nm INIT_ONCE , 35.Nm FINI_ONCE 36.Nd run a function exactly once 37.\" ------------------------------------------------------------ 38.Sh SYNOPSIS 39.In sys/once.h 40.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 41.Vt ONCE_DECL(control); 42.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 43.Ft int 44.Fn RUN_ONCE \ 45"once_t *control" "int (*init_func)(void)" 46.Ft int 47.Fn INIT_ONCE \ 48"once_t *control" "int (*init_func)(void)" 49.Ft void 50.Fn FINI_ONCE \ 51"once_t *control" "void (*fini_func)(void)" 52.\" ------------------------------------------------------------ 53.Sh DESCRIPTION 54.Fn RUN_ONCE 55provides a functionality similar to 56.Xr pthread_once 3 . 57It ensures that, for a given 58.Fa control , 59.Fn init_func 60is executed (successfully) exactly once. 61It is considered as a successful execution if and only if 62.Fn init_func 63returned 0. 64As long as there was no successful execution, 65.Fn RUN_ONCE 66will try again each time it is called. 67.Pp 68.Fn RUN_ONCE 69can sleep if it's called concurrently. 70.Pp 71.Fn INIT_ONCE 72is used in pair with 73.Fn FINI_ONCE . 74.Fn INIT_ONCE 75will only be run once similar to 76.Fn RUN_ONCE . 77.Fn FINI_ONCE 78will only be run at last time if it is called as many times as calling 79.Fn INIT_ONCE . 80When 81.Fn FINI_ONCE 82is executed, the next call to 83.Fn INIT_ONCE 84will be executed again. 85That is, 86.Fn INIT_ONCE 87and 88.Fn FINI_ONCE 89can be nested. 90.\" ------------------------------------------------------------ 91.Sh RETURN VALUES 92On failure, 93.Fn RUN_ONCE 94returns what 95.Fn init_func 96returned. 97Otherwise, it returns 0. 98.\" ------------------------------------------------------------ 99.Sh EXAMPLES 100The following example shows how 101.Fn RUN_ONCE 102is used. 103Regardless of how many times 104.Fn some_func 105is executed, 106.Fn init_func 107will be executed exactly once. 108.Bd -literal 109static int 110init_func(void) 111{ 112 113 /* 114 * do some initialization. 115 */ 116 117 return 0; /* success */ 118} 119 120int 121some_func(void) 122{ 123 static ONCE_DECL(control); 124 125 RUN_ONCE(&control, init_func); 126 127 /* 128 * we are sure that init_func has already been completed here. 129 */ 130} 131.Ed 132.\" ------------------------------------------------------------ 133.Sh SEE ALSO 134.Xr pthread_once 3 , 135.Xr condvar 9 , 136.Xr intro 9 137