does toltalk guarantee message ordering?

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2 total messages Started by Dorab Patel Tue, 28 Jul 1992 03:58

Author: Dorab Patel
Date: Tue, 28 Jul 1992 03:58

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do all the tooltalk clients in a scope get the messages in the same
order?  i.e., if two different clients generate a message each, at
approximately the same time, will all the clients in the scope get
the two messages in the same order?  i'm presuming that if the two
messages were generated by the SAME client, the messages would be
received by all clients in the same order.  if the message ordering
is consistent, is the serialization done at the ttdbserver (for file
scoped messages) and the ttsession (for session scoped messages)? or
is another method used for guaranteeing ordering?

'dorab

Re: does toltalk guarantee message ordering?

Author: Brian Holtz
Date: Tue, 28 Jul 1992 18:08

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In article <1992Jul28.035808.10587@cs.ucla.edu> dorab@hilo.cs.ucla.edu
(Dorab Patel) writes:

>do all the tooltalk clients in a scope get the messages in the same
>order?

For session-scoped notices, yes.

>i'm presuming that if the two
>messages were generated by the SAME client, the messages would be
>received by all clients in the same order.

For notices, yes.

No guarantees can be made for requests, because they can be rejected.

>if the message ordering is consistent, is the serialization done at
>the ttdbserver (for file scoped messages)

No serialization across different senders is done for file-scoped
messages.  (For a way around this problem, see below.)

>and the ttsession (for session scoped messages)?

Yes.

>or is another method used for guaranteeing ordering?

As you know, we did a demo that shows how to get the effect of
guaranteed global ordering of file-scoped notices:

 libCoEd is a C++ library that can turn any text editor into a shared
 text editor.  It is as far as I know the first fully distributed
 implementation of the dOPT algorithm (C.A. Ellis and S.J. Gibbs,
 "Concurrency Control in Groupware Systems", Proc. 1989 ACM SIGMOD,
 Int. Conf. on the Mgt. of Data).  dOPT allows you to do fully
 distributed simultaneous editing, without locking, as long as you can
   1) impose a full ordering on editing locations in your media type
      (e.g., text, bitmaps, spreadsheets, probably even tree-structured
      media like outlines or vector drawings),
   2) impose a full ordering on editing sites (by ToolTalk procID or
      some such), and
   3) guarantee (a la ToolTalk) that messages between sites will be
      delivered in order and exactly once.

 Any text editor that implements the CoEd ToolTalk protocol (e.g., by
 using libCoEd) can be a group editor with any other such conforming
 editor.

 CoEd uses the OLIT GUI toolkit and libCoEd to provide a simple shared
 text editor.

 Since CoEd and libCoEd were done as a ToolTalk demo, their source code
 is freely redistributable.  The source code is in
 ftp.cs.ucla.edu:/pub/CoEd.tar.Z.
--
Brian Holtz

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