Ack+Final returned with a sequence Fault
should then be added to complete proposal - that is indeed an option I
saw.
However... even the Fault could be
lost, and therefore the RMS may still try to send messages. I assume then that
the behavior is for RMD to resend the Fault+ Ack+Final each time.
Ø
While the RMS could send a
close() to get the final Ack, sending just an AckReq would do it too.
Right. So I guess we still need to say in
update to spec that sequence faults have the effect of closing the sequence.
(not terminate it).
The statement about semantics of closing becomes:
-
no "sequence"
message will be accepted anymore. If the sequence was Faulted at time it
closed, the sequence Fault will be resent back (according to policy) if RMS
keeps sending messages, and if so, must always include Ack+Final.
-
All sequence
operations are still accepted and processed as appropriate, until termination
occurs.
Thoughts?
-Jacques
From: Doug Davis
[mailto:dug@us.ibm.com]
Sent: Tuesday, August 16, 2005
5:40 PM
To: Jacques
Durand
Cc: ws-rx@lists.oasis-open.org
Subject: RE: [ws-rx] i0019 - a
proposal: (more complete)
I don't think I was totally clear - I viewed them as
being the same thing because (and this is where I probably wasn't clear) on a
Fault I assumed the RMD would close the sequence and send back a Fault with the
Ack+Final (which is what you say in your 2nd bullet). While the RMS could
send a close() to get the final Ack, sending just an AckReq would do it too.
So, whether the two issues are the same or not I view this solution solving
both of them.
-Doug
Jacques
Durand
<JDurand@us.fujitsu.com>
08/16/2005 07:50 PM
|
To
|
Jacques Durand
<JDurand@us.fujitsu.com>, Doug Davis/Raleigh/IBM@IBMUS,
ws-rx@lists.oasis-open.org
|
cc
|
|
Subject
|
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