Question

The workflow is being published as a wcf service, and I need to guarantee that workflows execute sequentially. Is there a way--in code or in the config--to guarantee the runtime doesn t launch two workflows concurrently?

Answer 1

There is no way to configure the runtime to limit the number of workflows in progress.

Consider though that its the responsibility of the workflow itself to control flow. Hence the workflow itself should have means to determine if another instance of itself is currently in progress.

I would consider creating an Activity that would transactionally attempt to update a DB record to the effect that an instance of this workflow is in progress. If it finds that another is currently in progress it could take the appropriate action. It could fail or it could queue itself using an EventActivity to be alerted when the previous workflow has completed.

Answer 2

You probably will need to check at workflow start for another running instance. If found, cancel it.

Answer 3

I don t agree that this needs to be handled at the WorkflowRuntime level. I like the idea of a custom Activity, sort of a MutexActivity that would be a CompositeActivity that has a DB backend. The first execution would log to the database it has a hold of the mutex. Subsequent calls would queue up their workflow IDs and then go idle. When the MutexActivity completes, it would release the Mutex, load up the next workflow in the queue and invoke the contained child activities.

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