121 lines
3.7 KiB
Groff
121 lines
3.7 KiB
Groff
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.\" $NetBSD: pthread_atfork.3,v 1.5 2008/04/30 13:10:50 martin Exp $
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.\"
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.\" Copyright (c) 2003 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Nathan J. Williams.
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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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd February 12, 2003
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.Dt PTHREAD_ATFORK 3
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.Os
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.Sh NAME
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.Nm pthread_atfork
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.Nd register handlers to be called when process forks
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In pthread.h
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.Ft int
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.Fn pthread_atfork "void (*prepare)(void)" "void (*parent)(void)" "void (*child)(void)"
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.Sh DESCRIPTION
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The
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.Fn pthread_atfork
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function registers the provided handler functions to be called when the
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.Xr fork 2
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function is called.
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Each of the three handlers is called at a different place in the
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.Xr fork 2
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sequence.
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The
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.Ar prepare
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handler is called in the parent process before the fork happens, the
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.Ar parent
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handler is called in the parent process after the fork has happened, and the
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.Ar child
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handler is called in the child process after the fork has happened.
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The
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.Ar parent
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and
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.Ar child
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handlers are called in the order in which they were registered, while the
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.Ar prepare
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handlers are called in reverse of the order in which they were registered.
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.Pp
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Any of the handlers given may be
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.Dv NULL .
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.Pp
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The intended use of
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.Fn pthread_atfork
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is to provide a consistent state to a child process from a multithreaded parent
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process where locks may be acquired and released asynchronously with respect to the
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.Xr fork 2
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call.
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Each subsystem with locks that are used in a child process should register
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handlers with
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.Fn pthread_atfork
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that acquires those locks in the
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.Ar prepare
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handler and releases them in the
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.Ar parent
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handler.
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.Sh RETURN VALUES
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The
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.Fn pthread_atfork
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function returns 0 on success and an error number on failure.
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.Sh ERRORS
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The following error code may be returned:
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.Bl -tag -width Er
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.It Bq Er ENOMEM
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Insufficient memory exists to register the fork handlers.
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.El
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.Sh SEE ALSO
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.Xr fork 2
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.Sh STANDARDS
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The
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.Fn pthread_atfork
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function conforms to
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.St -p1003.1c-95 .
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.Sh HISTORY
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The
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.Fn pthread_atfork
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function first appeared in
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.Nx 2.0 .
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.Sh CAVEATS
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After calling
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.Xr fork 2
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from a multithreaded process, it is only safe to call
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async-signal-safe functions until calling one of the
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.Xr exec 3
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functions.
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The
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.Fn pthread_*
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functions are not async-signal-safe, so it is not safe to use such functions
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in the
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.Ar child
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handler.
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.Sh BUGS
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There is no way to unregister a handler registered with
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.Fn pthread_atfork .
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