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Subject: RE: [wsbpel] invoke/receive-callback race conditions, even in the 1.1 sample (p.22)


Although the example does not use correlation and thus leaves the routing of the <receive operation="sendInvoice" /> to the correct instance unspecified, we have to assume as you point out that correlation is involved (and possibly fix the example).  Otherwise the receive does not actually work unless it creates a new process instance, in which case there is no race.  

So I think it would be helpful to restate your problem making the assumption of correlation.  Recasting the example using <flow> is compounding the confusion in my humble opinion.


-----Original Message-----
From: Eckenfels. Bernd [mailto:B.Eckenfels@seeburger.de] 
Sent: Friday, July 04, 2003 8:57 AM
To: wsbpel@lists.oasis-open.org
Subject: [wsbpel] invoke/receive-callback race conditions, even in the 1.1 sample (p.22)


in the 1.1 spec, there is a sample on p.22 featuring call back ports for the result of price calculation. This sample suffers from a possible race condition:

  <invoke operation="initiatePriceCalc" />
  <invoke operation="sendShippingPrice" />
  <receive operation="sendInvoice" />

In this sample, requesting a invoice by Purchase Order, the second invoke adding shipping infos, and the reply waiting for the calculated invoice. So depending on the runtime engine, the receive activity might not get activated before the response is already received. Besides the fact, that this sample is not dealing with correlations, it might be rewritten as:

  <receive />
    <invoke />
    <invoke />

But this still is open for a race condition (as the activation sequence of a flow is undefined).

So, we beed to address two issues here:

a) is it required for the enactment service to support receives which are depending (by link or sequence) on the completion of invokes. If yes, how deep this dependency should be allowed. If it is not required for the enactment, then the sample is illegally constructed.

b) if we do not allow the sequencing and declare the sample as broken, then an alternative notation with a flow may be used, but also requires some sematic definitions: 

'flows are activated top down, this meens if a receive activity in a flow is before the invoke (with no links), then engines have to gurantee, that the corellation entry is made before the service is invoked.'


'flows are activated, so that all ready receicves are invoked before ready invokes.'

We have the problem, that we can't use links to express a relationship like "if the receive has established the orrelation entry, then invoke". The other problem is, that my proposed regulation for flow does not help with receives, which are not directly nested below the flow. For example a 

    <receive />

does not reliable work with the "first all receive" nor with the "top down activation" definition.

I started this discussion, to ensure my understanding of the situation is correct. If you agree, I will raise a formal issue.

Note: this is also reláted to issue 31, because generating a UUID is a requirement for the b) solution.


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