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From: erc@pai.UUCP (Eric Johnson)
Newsgroups: comp.windows.x
Subject: Re: Interclient Communication
Summary: XSendEvent()
Keywords: Property SendEvent ClientMessage
Message-ID: <1506@pai.UUCP>
Date: 26 Oct 90 13:43:54 GMT
References: <880@kivax.UUCP>
Organization: Boulware Technologies, Inc., Burnsville, MN
Lines: 54

In article <880@kivax.UUCP>, koe@kivax.UUCP (Diana Koehler) writes:
> I am just working with the different mechanisms of 
> interclient communication. What method should I use
> -  to exchange data between clients ?
>    (Properties or XSendEvent, with type ClientMessage)

> -  to notify a client without sending data (in sense of semaphores)

     I'm assuming you mean you want to only send short messages
     between your clients. The X Window System is not intended to
     be a generic inter-process communication (IPC) system. If you want to
     send large amounts of data, you'll probably have a better time
     with sockets, streams, shared memory or some other
     IPC technique.

A common technique for X Window applications to exchange short messages
is to:

1) Append your application's window ID to a "known" property on the root 
window. By known property I mean a property that all your applications
agree to beforehand. The window ID is necessary for using
XSendEvent(). Window IDs also will change each time you run your
applications, so writing the window ID to a property solves the tough
problem of finding the window IDs of the applications you want
to communicate with.

2) Use XSendEvent() to send short messages to the applications
that have registered an interest in those messages (that is, those
applications that have appended their window IDs to the property
on the root window). The ClientMessage event type allows you to send
20 bytes of arbitrary data with each message. Another cute thing is to
send KeyPress/KeyRelease events to an application and pretned the
user actually typed the keys. (This is useful for application testing,
too.)

There's a whole chapter on sending events in Advanced X Window Applications
Programming (a book I'm responsible for). Send me e-mail if
you would like more information on this.

> Thanks
> Diana Koehler                     Tel.:   +49 7721 867034
> Mannesmann Kienzle GmbH
> Abt. 011.2                        e-mail: koe@kivax.UUCP
> Postfach 1640                             ..!mcsun!unido!kivax!koe
> D-7730 VS-Villingen                       ..!uunet!unido!kivax!koe

Hope this helps,
-Eric

-- 
Eric F. Johnson               phone: +1 612 894 0313    BTI: Industrial
Boulware Technologies, Inc.   fax:   +1 612 894 0316    automation systems
415 W. Travelers Trail        email: erc@pai.mn.org     and services
Burnsville, MN 55337 USA