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Re: [hyades-dev] Datacollection protocols and deadlock



Let me assure you and Mike that your concerns are being heard and I do
understand them.  I do want to make it clear that we are not far enough
along to even start discussing this yet.  Once we start putting the
commands in place, the interactions need to take these issues into
consideration.  Meanwhile, any further information/contribution you can
provide is appreciated but I do not want it to distract the group
prematurely.

Richard K. Duggan
Problem Determination Enablement
IBM Toronto Laboratory
External: 905-413-2396
Internal: 969-2396



                                                                           
             "Antony Miguel"                                               
             <antony.miguel@sc                                             
             apatech.com>                                               To 
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             eclipse.org                                                   
                                                                   Subject 
                                       [hyades-dev] Datacollection         
             05/07/2004 12:49          protocols and deadlock              
             PM                                                            
                                                                           
                                                                           
             Please respond to                                             
                hyades-dev                                                 
                                                                           
                                                                           




Mike and I are worried about the new protocol specifications for the Hyades
datacollection transport specification with respect to distributed
deadlock.

From what Andy said, agents will be sending around asynchronous messages
and eager readers on the agents' incoming streams are expected to prevent
deadlock.  A system like this can still deadlock.

Mike wants the Choreography Engine's transport layer and the Datacollection
Engine's transport layer to converge; partly so that the Datacollection
Engine can benefit from the Choreography Engine's deadlock free transport
layer and partly so that there is the potential for both engines to use the
same transport layer specification.

I don't entirely understand what the flow of communication will be in the
Datacollection Engine and it may be that the message flows for the
datacollection engine mean the datacollection engine is not able to
deadlock at points where the choreography engine is.  However, on the face
of it it does sound like there will be problems and the transport layer for
the Choreography Engine is deadlock free so picking it up guarantees we
won't see these problems at any point.

We need to discuss this and come to some agreement on it before we start
specifying layers too high up.  I think that layer 0 will probably be
unaffected as its only handshaking and simple point to point messaging but
we need to discuss this before we go too far with the layers above.

There doesn't seem to be a lot of common knowledge about these layers so I
think probably the fastest way to progress this stuff is for me to produce
a document that explains the deadlock protection layers in detail and then
when we've discussed that we can start to come up with some protocols for
them.

For the moment though, here is a quick description of the Choreography
Engine's bottom layers:

-----------------------------------
point to point transaction layer (including buffer planes - Merlin and
Schweitzer's algorithm)

-----------------------------------
finite-buffered (through remote acks) unidirectional streams

-----------------------------------
multiplexing (needed for acks above to not interfere with normal messages)
    e.g. data is sent on up + down stream 1, acks are sent on up + down
stream 2

-----------------------------------
point to point (e.g. socket connection)

-----------------------------------


This description probably isn't very enlightening to most but I'll email
out the detailed document as soon as I can.

I'd appreciate any agreement / disagreement / feedback from anyone
participating in the data collection protocol discussion.

cheers

Antony

antony.miguel@xxxxxxxxxxxxx





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