RE: [ws-rx] i0019 - a proposal: (more complete)

Ooops, backtrack this: something is missing in your proposal Doug, that I didn't catch before:

- remember this is the issue where termination is on sequence Fault from RMD side: the RMS does not even get a chance to do some closing.

- So I think we should also give all Sequence Faults a "closing" semantics, rather than an actual "termination" semantics. When getting the Fault, the RMS knows the sequence has closed, but can still send a "close" op to get a final Ack. Then it would have to Terminate the sequence (unless it lets inactivity or expiration time kick-in).

- Your proposal seems to be more appropriate for the twin issue - reworded Proposed-01 -, where RMS just wants the final tab after deciding to not use the sequence anymore, regardless of gaps and regardless of termination process (expiration, inactivity, or TerminateSequence if allowed here)

Jacques

From: Jacques Durand
Sent: Tuesday, August 16, 2005 3:20 PM
To: 'Doug Davis'; ws-rx@lists.oasis-open.org
Subject: RE: [ws-rx] i0019 - a proposal

Doug:

Overall that seems to do the trick.

More Inline <JD>

A related comment:

- the use of LastMessage marker appears now like a subcase of closing, where the RMD will close if (1) LastMessage was received, (2) all messages before were received.

- After we are done with i019, I think we should reconsider how useful LastMessage is (I guess a separate issue). My expectation here is to keep the protocol simple. At least, I would like i019 and your proposal to NOT be perceived as making the protocol more complex... as I believe it makes it possible to trade one feature ("LastMessage") for another ("Close").

Cheers,

Jacques

From: Doug Davis [mailto:dug@us.ibm.com]
Sent: Sunday, August 14, 2005 4:26 PM
To: ws-rx@lists.oasis-open.org
Subject: [ws-rx] i0019 - a proposal

For issue 19 we're really dealing with the communication of the state of the sequence between the RMD and the RMS. I think there are two situation we need to think about:
1 - a sequence w/o gaps
2 - a sequence with gaps

#1 is easy, when the RMS receives an Ack for the full range of messages that it has sent then it knows that the sequence is complete and it can send a Terminate knowing no new messages will be accepted by the RMD. In the absence of an ACK the RMS can always ask for one using an AckRequested thereby determine the RMD's state.

#2 seems to be the problem child. Lost (or delayed) Acks and Messages can play havoc with the RMS's perception of what the final state of the sequence is. For example, it may believe that message #3 (out of 6) was lost and doesn't care any more (for some reason), so it sends a TerminateSequence.

<JD> I thought TerminateSequence can't be sent out unless RMS get all messages acknowledged ? (hey, I am not the only one reading the spec in a "lax" way !! ;-)

However, if message #3 is just slow, and arrives at the RMD after the sending of the Terminate but before it arrives then the RMD's sequence state will differ from the RMS's. Sending a final Ack back to the RMS might not be sufficient since that might be lost as well.

<JD> In fact, the termination case for i019 is more of a SequenceFault that, at the time it occurs on RMD, leaves the RMS without an idea whether some missing messages were received since it got its last SequenceAck. But the solution is the same.

So, I'd like to propose the following:

Add a "Final" marker to the SequenceAck header (per Dan's suggestions). The inclusion of this element in the Ack is the RMD's way of telling the RMS that no new messages will be accepted into this sequence. This is true regardless of there being gaps in it or not.
Define a new operation: "Close". The RMS can send a "Close" to the RMD indicating that it would like to shutdown the sequence and request that no new messages be accepted. Notice that this is similar to a TerminateSequence in that they both shutdown the sequence but unlike a TerminateSeq, the "Close" will not do any resource reclamation - it just halts the delivery/processing of any new messages.

<JD> semantics of Close is: sequence will reject any future message (in effect freezing its state) except "operation" messages such as Close and TerminateSequence, to which it should respond as appropriate.

So, going back to situation #2, the RMS wants to close down the sequence despite there being gaps. It will send a "Close" to the RMD, which in turn responds with "Closed" plus an Ack. Note that the Ack will include the "Final" marker.

<JD> if the Closed is always accompanied by the SeqAck, then this Ack can be considered as final ("Final" marker is only cosmetic).

If this message (or the Close) is lost the RMS is free to send it over and over until it gets an Ack+Final since processing multiple ones has no negative impact. Upon receipt of the Ack+Final the RMS can then safely send a TerminateSequence without fear of any new messages arriving and changing its perception of the gaps in the sequence.

<JD> that means we change the rule of usage for TerminateSequence too.

Note that sending a "Close" for a sequence that doesn't have gaps doesn't cause any harm either - its an optional message that _can_ flow right before a TerminateSequence.
Thoughts? If people like this I'll write up a more formal proposal (spec changes).

<JD> I'm OK with this.

-Jacques

thanks
-Doug

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