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Subject: RE: [wsbpel] Issue 3 -- proposal for discussion
Yaron, May be we should instead forbid the name of the variable in getVariableData to be dynamic. It seems that this idea was raised in the F2F. I think that this is a path we should explore. Edwin > -----Original Message----- > From: Yaron Goland [mailto:ygoland@bea.com] > Sent: Wednesday, October 08, 2003 3:17 PM > To: 'Satish Thatte'; wsbpel@lists.oasis-open.org > Subject: RE: [wsbpel] Issue 3 -- proposal for discussion > > That's it! Thank you. When I wrote up the letter something > was really bugging me but I couldn't figure out what it was > and so eventually just sent the letter. Your letter reminded > me what was bugging me. > > Since one can use getVariableData functions whose > variableName is itself a variable one must use annotations > otherwise one has to persist all values. > > So the answer to the last question in my letter is - No, > static analysis cannot always determine when a compensation > handler has accessed a variable that has not been marked for > 'freezing'. Instead we will have to have runtime checking > that can throw a fault if a getVariableData function should > have a variableName argument whose value does not resolve to > a 'frozen' or 'live' value. > > Yaron > > > > > -----Original Message----- > > From: Satish Thatte [mailto:satisht@microsoft.com] > > Sent: Wednesday, October 08, 2003 1:26 PM > > To: ygoland@bea.com; wsbpel@lists.oasis-open.org > > Subject: RE: [wsbpel] Issue 3 -- proposal for discussion > > > > > > Yaron, > > > > It should be fairly straightforward to detect which non-local > > variables are actually used in compensation handlers and > persist only > > those. What you are suggesting is an extra annotation that allows > > additional verification of intent via redundancy. Seems OK > though a > > bit onerous, and nothing at all to do with cost. Do other > people have > > opinions? > > > > The bigger issue for cost is detecting when a scope snapshot is no > > longer needed because there is no "path" left to invoke it. > In other > > words, snapshot GC. > > > > Satish > > > > -----Original Message----- > > From: Yaron Goland [mailto:ygoland@bea.com] > > Sent: Wednesday, October 08, 2003 1:10 PM > > To: Satish Thatte; wsbpel@lists.oasis-open.org > > Subject: RE: [wsbpel] Issue 3 -- proposal for discussion > > > > Is one of the practical consequences of proposal 2 that all scope > > variables must be persisted when the scope successfully completes if > > either: > > A) The scope has a non-default compensation handler or > > B) The scope's variables are 'visible' from a scope with a > > non-default compensation handler (e.g. imagine if S1 and S3 had > > compensation handlers but S2 just had a default > compensation handler. > > In that case S2 would still need to persist its variables > since they > > would be 'visible' from S3)? > > > > Doesn't this seem a bit expensive? BPEL processes can run > for months > > or even years, building up lots of scopes all of whose > variables would > > have to be persisted. > > > > Might it not be more economical to include an attribute that can be > > included on variable declarations to define which variables > should be > > available for use by compensation handlers? > > > > Couldn't static analysis then catch cases where a > compensation handler > > attempts to access a variable which has not been marked as being > > available for compensation handlers? > > > > Thanks, > > > > Yaron > > > > > -----Original Message----- > > > From: Satish Thatte [mailto:satisht@microsoft.com] > > > Sent: Wednesday, October 08, 2003 7:07 AM > > > To: wsbpel@lists.oasis-open.org > > > Subject: RE: [wsbpel] Issue 3 -- proposal for discussion > > > > > > > > > One more time - this time with a more accessible JPEG > > picture courtesy > > > of Sid Askary. > > > > > > Better formatted version of the same mail .. > > > > > > BPEL currently specifies that a compensation handler lives in a > > > snapshot world in which the state of the associated scope and all > > > enclosing scopes has been preserved as it was when the associated > > > scope completed. > > > There is an outstanding BPEL issue (Issue#3) that points out that > > > there is a need for compensation handlers to affect and > be affected > > > by the "current state of the world". > > > > > > Proposal #1: The proposal on the table has been to add > inbound and > > > outbound parameters to compensation handlers to allow invokers of > > > compensation to send data into and get data out of the > compensation > > > process. > > > > > > Proposal #2: Choreology put an alternative proposal on the table. > > > Restated, it basically says that compensation handlers > > always see the > > > current state of the world. The current state of the world for > > > completed scopes is their state as it was at the time of > completion. > > > They are in suspended animation because their > compensation handlers > > > are still alive and therefore their execution may "continue" in > > > compensation mode. Thus for enclosing scopes the compensation > > > handler > > either sees > > > live state (if the scope is not completed) or the state > of the scope > > > as it was when that scope completed. > > > > > > In the attached picture showing three nested scopes S1, > S2 and S3, > > > their compensation handlers C1, C2, C3, and failure > handlers F1 and > > > F2, we may have an error handling call stack F1->C2->C3. In that > > > case > > > C3 will see > > > the state of S2 as it was when S2 completed. However > that is also > > > what > > > C2 is seeing and C2 has called C3, therefore there is a > > consistency of > > > visible state in the call stack. > > > > > > The positives and negatives of these two proposals mirror each > > > other. A positive aspect of the second proposal is that > parameters > > > are not needed for data flow to and from live state to > compensation > > > handlers, and compensation handlers with live state > contact can be > > > used in default compensation, unlike the first proposal. The > > > negative > > aspect is that > > > compensation handlers will now participate in concurrency control > > > issues relating to live state, and will need to use serializable > > scopes when > > > they touch non-local state, again unlike the first proposal. The > > > concurrency control problem also has an impact on Issue#10 > > which deals > > > with serialization of compensation handlers. > > > > > > On the whole, given the alternatives, the second alternative is > > > preferable, especially because it maintains default compensation > > > semantics. I propose to resolve Issue 3 along the lines of the > > > Proposal #2. > > > > > > Satish > > > > > > > > > > > > > > > > > > > > > > >
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