Path: utzoo!utgpu!water!watmath!clyde!burl!codas!pdn!pdnbah!reese
From: reese@pdnbah.UUCP (Don Reese)
Newsgroups: comp.sys.amiga
Subject: Re: IPC - A proposal
Keywords: IPC PIPES SOCKETS QUEUES SEMAPHORES
Message-ID: <2609@pdn.UUCP>
Date: 23 Mar 88 14:48:09 GMT
References: <5375@well.UUCP> <5377@well.UUCP>
Sender: usenet@pdn.UUCP
Reply-To: reese@pdnbah.UUCP (Don Reese)
Organization: Paradyne Corporation, Largo, Florida
Lines: 40

In article <5377@well.UUCP> ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab) writes:
>	UNIX achieves IPC (usually) through pipes.  One program's stdout is
>connected to another program's stdin.  On UNIX, this works great since, in
>most cases, all user I/O through the program is through stdin and stdout.
>
What do you consider a pipe?  Unix provides many methods of interprocess
communications.  Here is a list of the more widely used methods:
	Pipe:	A method of passing output from one program (usually
		standard out but not required) to the input of another
		program (usually standard input but also not required).
		General implementation done using a tempory fixed size
		file.
	Named Pipe:  Simular method of passing output from one program
		to input of another program but using a predetermined
		file name for the purpose.
	Queues:	Interprocess communications consisting of messages that
		are passed between programs across message queues.
		Involves creation of internal queues within the OS and
		methods of accessing the queues.
	Sockets: Bidirectional data stream between two processes simular
		to a pipe.  Within Unix sockets are normally used to
		communicate between processes that may not be running on
		the same processor (networked processors usually using
		a LAN).
	Semaphores and Shared Memory:  Two processes attach to the same
		memory location and control updates through the setting
		and checking of flags internal to the OS.

I am probably missing other methods, but the point here is that several
methods of interprocess communications exist under Unix.  Each has it's
advantages or disadvantages depending upon the needs of the system being
designed.  If you are considering adding IPC facilities, consider adding
multiple methods.

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