1.\" $NetBSD: pthread_atfork.3,v 1.5 2008/04/30 13:10:50 martin Exp $ 2.\" 3.\" Copyright (c) 2003 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Nathan J. Williams. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd February 12, 2003 31.Dt PTHREAD_ATFORK 3 32.Os 33.Sh NAME 34.Nm pthread_atfork 35.Nd register handlers to be called when process forks 36.Sh LIBRARY 37.Lb libc 38.Sh SYNOPSIS 39.In pthread.h 40.Ft int 41.Fn pthread_atfork "void (*prepare)(void)" "void (*parent)(void)" "void (*child)(void)" 42.Sh DESCRIPTION 43The 44.Fn pthread_atfork 45function registers the provided handler functions to be called when the 46.Xr fork 2 47function is called. 48Each of the three handlers is called at a different place in the 49.Xr fork 2 50sequence. 51The 52.Ar prepare 53handler is called in the parent process before the fork happens, the 54.Ar parent 55handler is called in the parent process after the fork has happened, and the 56.Ar child 57handler is called in the child process after the fork has happened. 58The 59.Ar parent 60and 61.Ar child 62handlers are called in the order in which they were registered, while the 63.Ar prepare 64handlers are called in reverse of the order in which they were registered. 65.Pp 66Any of the handlers given may be 67.Dv NULL . 68.Pp 69The intended use of 70.Fn pthread_atfork 71is to provide a consistent state to a child process from a multithreaded parent 72process where locks may be acquired and released asynchronously with respect to the 73.Xr fork 2 74call. 75Each subsystem with locks that are used in a child process should register 76handlers with 77.Fn pthread_atfork 78that acquires those locks in the 79.Ar prepare 80handler and releases them in the 81.Ar parent 82handler. 83.Sh RETURN VALUES 84The 85.Fn pthread_atfork 86function returns 0 on success and an error number on failure. 87.Sh ERRORS 88The following error code may be returned: 89.Bl -tag -width Er 90.It Bq Er ENOMEM 91Insufficient memory exists to register the fork handlers. 92.El 93.Sh SEE ALSO 94.Xr fork 2 95.Sh STANDARDS 96The 97.Fn pthread_atfork 98function conforms to 99.St -p1003.1c-95 . 100.Sh HISTORY 101The 102.Fn pthread_atfork 103function first appeared in 104.Nx 2.0 . 105.Sh CAVEATS 106After calling 107.Xr fork 2 108from a multithreaded process, it is only safe to call 109async-signal-safe functions until calling one of the 110.Xr exec 3 111functions. 112The 113.Fn pthread_* 114functions are not async-signal-safe, so it is not safe to use such functions 115in the 116.Ar child 117handler. 118.Sh BUGS 119There is no way to unregister a handler registered with 120.Fn pthread_atfork . 121