[unix-history] / usr / doc / ipc / 1.t

.ds LH "4.2BSD IPC Primer
.ds RH Introduction
.LP
.nr H1 1
.bp
.ds RF "Leffler/Fabry/Joy
.ds LF "DRAFT of \*(DY
.ds CF "
.LG
.B
.ce
1. INTRODUCTION
.sp 2
.R
.NL
One of the most important parts of 4.2BSD is the interprocess
communication facilities.  These facilities are the result of
more than two years of discussion and research.  The facilities
provided in 4.2BSD incorporate many of the ideas from current
research, while trying to maintain the UNIX philosophy of
simplicity and conciseness.  It is hoped that
the interprocess communication
facilities included in 4.2BSD will establish a
standard for UNIX.  From the response to the design,
it appears many organizations carrying out
work with UNIX are adopting it.
.PP
UNIX has previously been very weak in the area of interprocess
communication.  Prior to the 4.2BSD facilities, the only
standard mechanism which allowed two processes to communicate were
pipes (the mpx files which were part of Version 7 were
experimental).  Unfortunately, pipes are very restrictive
in that
the two communicating processes must be related through a
common ancestor.
Further, the semantics of pipes makes them almost impossible
to maintain in a distributed environment. 
.PP
Earlier attempts at extending the ipc facilities of UNIX have
met with mixed reaction.  The majority of the problems have
been related to the fact these facilities have been tied to
the UNIX file system; either through naming, or implementation.
Consequently, the ipc facilities provided in 4.2BSD have been
designed as a totally independent subsystem.  The 4.2BSD ipc
allows processes to rendezvous in many ways. 
Processes may rendezvous through a UNIX file system-like
name space (a space where all names are path names)
as well as through a
network name space.  In fact, new name spaces may
be added at a future time with only minor changes visible
to users.  Further, the communication facilities 
have been extended to included more than the simple byte stream
provided by a pipe-like entity.  These extensions have resulted
in a completely new part of the system which users will need
time to familiarize themselves with.  It is likely that as
more use is made of these facilities they will be refined;
only time will tell.
.PP
The remainder of this document is organized in four sections.  
Section 2 introduces the new system calls and the basic model
of communication.  Section 3 describes some of the supporting
library routines users may find useful in constructing distributed
applications.  Section 4 is concerned with the client/server model
used in developing applications and includes examples of the
two major types of servers.  Section 5 delves into advanced topics
which sophisticated users are likely to encounter when using
the ipc facilities.
Commit	Line	Data
f0b8d567 C	1	.ds LH "4.2BSD IPC Primer
	2	.ds RH Introduction
	3	.LP
	4	.nr H1 1
	5	.bp
	6	.ds RF "Leffler/Fabry/Joy
	7	.ds LF "DRAFT of \*(DY
	8	.ds CF "
	9	.LG
	10	.B
	11	.ce
	12	1. INTRODUCTION
	13	.sp 2
	14	.R
	15	.NL
	16	One of the most important parts of 4.2BSD is the interprocess
	17	communication facilities. These facilities are the result of
	18	more than two years of discussion and research. The facilities
	19	provided in 4.2BSD incorporate many of the ideas from current
	20	research, while trying to maintain the UNIX philosophy of
	21	simplicity and conciseness. It is hoped that
	22	the interprocess communication
	23	facilities included in 4.2BSD will establish a
	24	standard for UNIX. From the response to the design,
	25	it appears many organizations carrying out
	26	work with UNIX are adopting it.
	27	.PP
	28	UNIX has previously been very weak in the area of interprocess
	29	communication. Prior to the 4.2BSD facilities, the only
	30	standard mechanism which allowed two processes to communicate were
	31	pipes (the mpx files which were part of Version 7 were
	32	experimental). Unfortunately, pipes are very restrictive
	33	in that
	34	the two communicating processes must be related through a
	35	common ancestor.
	36	Further, the semantics of pipes makes them almost impossible
	37	to maintain in a distributed environment.
	38	.PP
	39	Earlier attempts at extending the ipc facilities of UNIX have
	40	met with mixed reaction. The majority of the problems have
	41	been related to the fact these facilities have been tied to
	42	the UNIX file system; either through naming, or implementation.
	43	Consequently, the ipc facilities provided in 4.2BSD have been
	44	designed as a totally independent subsystem. The 4.2BSD ipc
	45	allows processes to rendezvous in many ways.
	46	Processes may rendezvous through a UNIX file system-like
	47	name space (a space where all names are path names)
	48	as well as through a
	49	network name space. In fact, new name spaces may
	50	be added at a future time with only minor changes visible
	51	to users. Further, the communication facilities
	52	have been extended to included more than the simple byte stream
	53	provided by a pipe-like entity. These extensions have resulted
	54	in a completely new part of the system which users will need
	55	time to familiarize themselves with. It is likely that as
	56	more use is made of these facilities they will be refined;
	57	only time will tell.
	58	.PP
	59	The remainder of this document is organized in four sections.
	60	Section 2 introduces the new system calls and the basic model
	61	of communication. Section 3 describes some of the supporting
	62	library routines users may find useful in constructing distributed
	63	applications. Section 4 is concerned with the client/server model
	64	used in developing applications and includes examples of the
65	two major types of servers. Section 5 delves into advanced topics
66	which sophisticated users are likely to encounter when using
67	the ipc facilities.