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1.1     ! root        1: .\" Copyright (c) 1986 The Regents of the University of California.
        !             2: .\" All rights reserved.
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        !            12: .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
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        !            16: .\"    @(#)1.t 1.4 (Berkeley) 3/7/89
        !            17: .\"
        !            18: .\".ds LH "4.3BSD IPC Primer
        !            19: .\".ds RH Introduction
        !            20: .\".ds RF "Leffler/Fabry/Joy
        !            21: .\".ds LF "\*(DY
        !            22: .\".ds CF "
        !            23: .nr H1 1
        !            24: .LP
        !            25: .bp
        !            26: .LG
        !            27: .B
        !            28: .ce
        !            29: 1. INTRODUCTION
        !            30: .sp 2
        !            31: .R
        !            32: .NL
        !            33: One of the most important additions to UNIX in 4.2BSD was interprocess
        !            34: communication.
        !            35: These facilities were the result of
        !            36: more than two years of discussion and research.  The facilities
        !            37: provided in 4.2BSD incorporated many of the ideas from current
        !            38: research, while trying to maintain the UNIX philosophy of
        !            39: simplicity and conciseness.
        !            40: The current release of Berkeley UNIX, 4.3BSD,
        !            41: completes some of the IPC facilities
        !            42: and provides an upward-compatible interface.
        !            43: It is hoped that the interprocess communication
        !            44: facilities included in 4.3BSD will establish a
        !            45: standard for UNIX.  From the response to the design,
        !            46: it appears many organizations carrying out
        !            47: work with UNIX are adopting it.
        !            48: .PP
        !            49: UNIX has previously been very weak in the area of interprocess
        !            50: communication.  Prior to the 4BSD facilities, the only
        !            51: standard mechanism which allowed two processes to communicate were
        !            52: pipes (the mpx files which were part of Version 7 were
        !            53: experimental).  Unfortunately, pipes are very restrictive
        !            54: in that
        !            55: the two communicating processes must be related through a
        !            56: common ancestor.
        !            57: Further, the semantics of pipes makes them almost impossible
        !            58: to maintain in a distributed environment. 
        !            59: .PP
        !            60: Earlier attempts at extending the IPC facilities of UNIX have
        !            61: met with mixed reaction.  The majority of the problems have
        !            62: been related to the fact that these facilities have been tied to
        !            63: the UNIX file system, either through naming or implementation.
        !            64: Consequently, the IPC facilities provided in 4.3BSD have been
        !            65: designed as a totally independent subsystem.  The 4.3BSD IPC
        !            66: allows processes to rendezvous in many ways. 
        !            67: Processes may rendezvous through a UNIX file system-like
        !            68: name space (a space where all names are path names)
        !            69: as well as through a
        !            70: network name space.  In fact, new name spaces may
        !            71: be added at a future time with only minor changes visible
        !            72: to users.  Further, the communication facilities 
        !            73: have been extended to include more than the simple byte stream
        !            74: provided by a pipe.  These extensions have resulted
        !            75: in a completely new part of the system which users will need
        !            76: time to familiarize themselves with.  It is likely that as
        !            77: more use is made of these facilities they will be refined;
        !            78: only time will tell.
        !            79: .PP
        !            80: This document provides a high-level description
        !            81: of the IPC facilities in 4.3BSD and their use.
        !            82: It is designed to complement the manual pages for the IPC primitives
        !            83: by examples of their use.
        !            84: The remainder of this document is organized in four sections.  
        !            85: Section 2 introduces the IPC-related system calls and the basic model
        !            86: of communication.  Section 3 describes some of the supporting
        !            87: library routines users may find useful in constructing distributed
        !            88: applications.  Section 4 is concerned with the client/server model
        !            89: used in developing applications and includes examples of the
        !            90: two major types of servers.  Section 5 delves into advanced topics
        !            91: which sophisticated users are likely to encounter when using
        !            92: the IPC facilities.

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