Newsgroups: comp.parallel.pvm
From: Stefan Hinker <hinker@informatik.uni-wuerzburg.de>
Subject: Re: pvm_send and pvm_mcast
Organization: University of Wuerzburg, Germany
Date: 5 Jan 1996 09:29:00 GMT
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Message-ID: <4cir0s$qq9@winx03.informatik.uni-wuerzburg.de>

Hi Andreas!

adilger@enel.ucalgary.ca (Andreas Dilger) wrote:
>to all the systems with pvm_mcast().  The problem I'm having is that
>the messages sent by pvm_mcast() are arriving before those sent by
>pvm_send(), even though they were sent later.  I thought PVM was guaranteed
>to preserve message order?  I'm using pvm 3.3.10 on both hosts.  The
>  master                           slaves
> --------                         --------
>  pvm_send() msg1 to slave1
>  pvm_send() msg1 to slave2
>  pvm_send() msg1 to slave3
>
>  pvm_mcast() msg2 to all slaves   pvm_trecv(-1,-1)  gets msg2
>                                   pvm_trecv(-1,-1)  gets msg1
>
>Is this a known problem/limitation/feature?  I suppose I could use

No, this is neither a bug nor a feature, its just a common thing in distributed
algorithms.  Use different message-tags or some kind of synchronizing 
logic.

>pvm_send() to all the machines independently rather than pvm_mcast(),
>but this, of course, would be slower.

I doubt it would be slower.  It's just more convenient. pvm_mcast uses one 
message per receiver, so there is just as much load on the net.

Greetings,
Stefan
-- 
===============================================================================
Stefan Hinker                         email: hinker@informatik.uni-wuerzburg.de
                Unix? Still working on it  :-))
===============================================================================


