Replicator Tips and Tricks

re: Replicator Tips and Tricks

slavik — Tue, 07 Nov 2006 15:38:30 GMT

Thanks for the tips on the replicator.

I was trying to implement some auction procedure using it and now wonder if my scenario is correct. You can see the workflow at:

http://static.flickr.com/121/290421062_d9a2d5d66c.jpg?v=0

The first client schedules the auction and then the others are sending their bids, and I'm using webServiceInput-Output. The problem is that after the first client will be answered by the web service, the replicator does not wait for the inputs from clients. I completes its children (fires the events) and completes in the end.

In the case if I move the replicator on first place in the workflow it waits for only the first replicated webServiceInput-Output and then instantly completes all the other children without receiving input from clients.

I'm using cookies in this scenario to root the requests to the workflow, but despite the rigth cookie names and values the published workflow doesn't work as expected. Is the solution incorrect?

re: Replicator Tips and Tricks

ntalbert — Tue, 07 Nov 2006 20:51:09 GMT

slavik, the long story short is that you cannot use WebServiceInput/WebServiceOutput inside a Replicator. The reason is that these activities do not support correlation in any manner - in your scenario there is no way to correctly route one client's request to a specific WSInput. For more information on this see correlation.

If you want to enable the scenario you mention you will be better off using HandleExternalEventActivity and CallExternalMethodActivity and writing your own web service host. While the latter part of this sounds like a major undertaking, writing your own simple web service based host is actually not that bad. Consider the following:

public class SomeService : WebService

{

private WorkflowRuntime runtime;

public WorkflowRuntime Runtime

{

get

{

// You can either specify a config section or do programmatic configuration here

if (runtime == null) runtime = new WorkflowRuntime();

return runtime;

}

[WebMethod]

public BidResult EnterBid(Guid instanceId, string clientId, decimal bidAmount)

{

BidService bidServ = Runtime.GetService<BidService>();

return bidServ.EnterBid(Guid instanceId, clientId, bidAmount);

}

Note that the code above is somewhat simplified (config of runtime is left out, BidService implementation is left out, actually getting to BidService will require accessing ExternalDataExchangeService) but this is the psuedocode that will get you to where you want to be.

BidService is meant to be an ExternalDataExchange service. EnterBid, for example, would raise an event into the workflow and then block waiting for the corresponding response to come back out. You can model this as such:

// EnterBid style code

dictionaryOfWaitHandles.Add(responseIdentifier, new ManualResetEvent(false));

someEvent(...) // one of the parameters is the "response identifier"

dictionaryOfWaitHandles[responseIdentifier].WaitOne();

dictionaryOfWaitHandles.Remove(responseIdentifier);

object result = dictionaryOfResponses[responseIdentifier];

dictionaryOfResponses.Remove(responseIdentifier);

return result;

// CallExternalMethodActivity targetted method which handles the "response"

dictionaryOfResponses.Add(responseIdentifier, response);

dictionaryOfWaitHandles[responseIdentifier].Set();

Again, this is a very simple approach - it assumes a single output, assumes you can block the thread, assumes you aren't using the ManualScheduler, etc. But, this is the basic idea on which you can build what you are looking for.

re: Replicator Tips and Tricks

slavik — Wed, 08 Nov 2006 18:28:10 GMT

Thanks. I supposed that the message is probably "consumed by all the replicated instances at the same time" which means there's no correlation support. But thought there might be some workaround or I'm making some mistake in the scenario. It's bad that the documentation never says that about the webServiceInput.

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