107 lines
4.8 KiB
Perl
107 lines
4.8 KiB
Perl
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.\" Copyright (c) 1986, 1993
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.\" The Regents of the University of California. 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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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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.\" @(#)1.t 8.1 (Berkeley) 8/14/93
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.\"
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.\".ds LH "4.4BSD IPC Primer
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.\".ds RH Introduction
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.\".ds RF "Leffler/Fabry/Joy
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.\".ds LF "\*(DY
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.\".ds CF "
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.nr H1 1
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.LP
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.bp
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.LG
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.B
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.ce
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1. INTRODUCTION
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.sp 2
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.R
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.NL
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One of the most important additions to UNIX in 4.2BSD was interprocess
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communication.
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These facilities were the result of
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more than two years of discussion and research. The facilities
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provided in 4.2BSD incorporated many of the ideas from current
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research, while trying to maintain the UNIX philosophy of
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simplicity and conciseness.
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The 4.3BSD release of Berkeley UNIX
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improved upon some of the IPC facilities
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while providing an upward-compatible interface.
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4.4BSD adds support for ISO protocols and IP multicasting.
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The BSD interprocess communication
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facilities have become a defacto standard for UNIX.
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.PP
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UNIX has previously been very weak in the area of interprocess
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communication. Prior to the 4BSD facilities, the only
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standard mechanism which allowed two processes to communicate were
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pipes (the mpx files which were part of Version 7 were
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experimental). Unfortunately, pipes are very restrictive
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in that
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the two communicating processes must be related through a
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common ancestor.
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Further, the semantics of pipes makes them almost impossible
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to maintain in a distributed environment.
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.PP
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Earlier attempts at extending the IPC facilities of UNIX have
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met with mixed reaction. The majority of the problems have
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been related to the fact that these facilities have been tied to
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the UNIX file system, either through naming or implementation.
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Consequently, the IPC facilities provided in 4.2BSD were
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designed as a totally independent subsystem. The BSD IPC
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allows processes to rendezvous in many ways.
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Processes may rendezvous through a UNIX file system-like
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name space (a space where all names are path names)
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as well as through a
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network name space. In fact, new name spaces may
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be added at a future time with only minor changes visible
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to users. Further, the communication facilities
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have been extended to include more than the simple byte stream
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provided by a pipe. These extensions have resulted
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in a completely new part of the system which users will need
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time to familiarize themselves with. It is likely that as
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more use is made of these facilities they will be refined;
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only time will tell.
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.PP
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This document provides a high-level description
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of the IPC facilities in 4.4BSD and their use.
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It is designed to complement the manual pages for the IPC primitives
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by examples of their use.
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The remainder of this document is organized in four sections.
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Section 2 introduces the IPC-related system calls and the basic model
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of communication. Section 3 describes some of the supporting
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library routines users may find useful in constructing distributed
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applications. Section 4 is concerned with the client/server model
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used in developing applications and includes examples of the
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two major types of servers. Section 5 delves into advanced topics
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which sophisticated users are likely to encounter when using
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the IPC facilities.
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