Re: query on Message queues

From: Gordon Burditt (gordonb.icjmt_at_burditt.org)
Date: 08/29/05 

Date: Mon, 29 Aug 2005 18:37:36 -0000

> I read one statement about message queues that "Message queues
>can be used between related and unrelated processes running on a
>machine"
> I want to know what is related and unrelated processes mean?

Processes are related if one is the parent or child of another, or
they are both child processes of a common ancestor. (Ok, nitpickers,
init is a common ancestor of all processes on the same machine, but
it's not generally too cooperative about setting up communication
between processes.)

Unnamed pipes can be used as a communication mechanism between
related processes, but it requires the common ancestor to create
the pipe and pass down the open file descriptor to the processes
doing the communicating.

>what are the examples for both related and unrelated processes on linux
>OS?

Related processes include a bunch of processes started by your shell
in response to a long, complicated pipeline command. Unrelated
processes include something forked by your mail client communicating
with the SMTP daemon on the local machine, the resolver code in
your process talking to the local nameserver, or your Mozilla client
talking to the local (caching) instance of Apache. Generally,
something called a "daemon" is unrelated to the processes it
communicates with (which might be on another host, also), although
there may also be communication between the "dispatcher" daemon
process (often listens on a socket) and "worker" daemon processes
(actually do requests) which may work more like "related process"
communication.

                                        Gordon L. Burditt

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