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When we start doing this two way style of messaging, we now open up to start modeling some interesting business problems. In the previous post, you'll note that I did not include the code, because I mentioned we needed to be more clever in scenarios where we listen in parallel. First, a brief diversion into how the Receive activity works. Everybody remembers the workflow queues, the technology that underlies all communication between a host and a workflow instance. The Receive activity works by creating a queue that the WorkflowServiceHost (specifically the WorkflowOperationInvoker) will use to send the message received off the wire into the workflow. Now, the Receive activity normally just creates a queue that is named the same as the operation the Receive activity is bound to. However, if we have two Receive activities listening for the same operation at the same time, no longer is a single queue useful to route responses back as we want to route to the correct Receive activity instance. There is property on the Receive activity called ContextToken. Normally this is null in the simple case. However, when we want our Receive activity to operate in parallel, we need to indicate that it needs to be smarter when it creates a queue. By setting this property (you can just type in a name, and then select the common owner all of the parallel receive's share. This will cause the Receive activity to create a queue named Read More...
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In this post , mstiefel asked the following: # re: Implementing the N of M Pattern in WF Since you are not looping, do you have to use the ActivityExecutionContextManager to generate a new context for the child activities? Couldn't you use the context passed into the Execute method? Friday, July 06, 2007 7:54 PM by mstiefel If I were creating a parallel activity, and simply wanted to execute a number of distinct child activities, I would just use the passed in context as you suggest to schedule execution of each of the activities. The difference here is subtle, and that is I don't have distinct child activities, I have one child activity which I need to clone m times and execute those cloned children separately. The need to create the context is so that each one of those clones maintains it's own execution context, what variables are where, who is in what state, etc. This is important while executing, and while after completion in the need where I want to compensate for the individual activities. This line ActivityExecutionContext newContext = aecm.CreateExecutionContext( this .Activities[0]); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; Read More...
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The second in my series of alternate execution patterns ( part 1 ) I recently worked with a customer who was implementing what I would call a "basic" human workflow system. It tracked approvals, rejections and managed things as they moved through a customizable process. It's easy to build workflows like this with an Approval activity, but they wanted to implement a pattern that's not directly supported out of the box. This pattern, which I have taken to calling "n of m", is also referred to as a " Canceling partial join for multiple instances " in the van der Aalst taxonomy. The basic description of this pattern is that we start m concurrent actions, and when some subset of those, n, complete, we can move on in our process and cancel the other concurrent actions. A common scenario for this is where I want to send a document for approval to 5 people, and when 3 of them have approved it, I can move on. This comes up frequently in human or task-based workflows. There are a couple of "business" questions which have to be answered as well, the implementation can support any set of answers for this: What happens if an individual rejects? Does this stop the whole group from completing, or is it simply noted as a "no" vote? How should delegation be handled? Some business want this to break out from the approval process at this point. The first approach the customer took was to use the ConditionedActivityGroup (CAG). The CAG is probably one of the most sophisticated out of the box activities Read More...
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How do I do this? A lot of times people get stuck with the impression that there are only two workflow models available: sequential and state machine. True, out of the box these are the two that are built in, but only because there are is a set of common problems that map nicely into their execution semantics. As a result of these two being "in the box," I often see people doing a lot of very unnatural things in order to fit their problem into a certain model. The drawing above illustrates the flow of one such pattern. In this case, the customer wanted parallel execution with two branches ((1,3) and (2,5)). But, they had an additional factor that played in here, 4 could execute, but it could only execute when both 1 and 2 had completed. 4 didn't need to wait for 3 and 5 to finish, 3 and 5 could take a long period of time, so 4 could at least start once 1 and 2 were completed. Before we dive into a more simple solution, let's look at some of the ways they tried to solve the problem, in an attempt to use "what's in the box." The "While-polling" approach The basic idea behind this approach is that we will use a parallel activity, and in the third branch we will place a while loop that loops on the condition of "if activity x is done" with a brief delay activity in there so that we are not busy polling. What's the downside to this approach: The model is unnatural, and gets more awkward given the complexity of the process (what do we do if activity 7 has a dependency on 4 and 5) The Read More...
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