Thinking and Processing in Parallel Wrap Your Head Around WF 4.0 Concurrency. Brian Noyes IDesign Inc (

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1 Thinking and Processing in Parallel Wrap Your Head Around WF 4.0 Concurrency Brian Noyes IDesign Inc ( About Brian Chief Architect IDesign Inc. ( Microsoft Regional Director ( Microsoft MVP Connected Systems Publishing Developing Applications with Windows Workflow Foundation, LiveLessons training DVD, June 2007 Smart Client Deployment with ClickOnce, Addison Wesley, January 2007 Data Binding in Windows Forms 2.0, Addison Wesley, January 2006 MSDN Magazine, MSDN Online, CoDe Magazine, The Server Side.NET, asp.netpro, Visual Studio Magazine Speaking Blog: Microsoft TechEd US, Europe, Malaysia, Visual Studio Connections, DevTeach, INETA Speakers Bureau, MSDN Webcasts 1

2 Workflow and Concurrency Workflow is typically asynchronous work Workflow executes asychronously from the code that invoked or called it A unit of work or business process that executes independently of the spawning process or thread Workflows can be executed synchronously in WF 4 with the WorkflowInvoker Treat it as a chunk of business logic you invoke 2

3 Workflows and Callers Child Workflow Step 1 Step 2 Parent Workflow Start Process Invoke Sub-Process Aggregate Results Notify Client Client App WF and Multithreading WF is a VERY multithreaded execution environment Separate threads for: Host Each workflow (and its runtime instance) Activities* * WF 4.0 supports a true async model for execution within activities 3

4 Multithreading Concerns Concurrent access to memory One thread reads state from an object Another thread writes state to an object Concurrency Solutions Don t share state in memory across threads Synchronization locks Monitor, Mutex, Semaphore, etc. Auto-dispatch Thread marshalling by.net Framework to a safe thread UI Technologies SynchronizationContext class 4

5 WF Runtime obtains an IO completion port thread and uses it to run a single workflow instance No more singleton model for the runtime Thread yielded back to the pool when workflow goes idle New thread retrieved when workflow ready to run again Workflow SynchronizationContext used for thread marshalling across threads 5

6 WF Host Concurrency Host can have its own threads Multiple threads can interact with the WF Runtime Multiple threads may call into a running workflow WF Services Host may be notified on multiple threads when workflow runtime events occur No guarantee of what thread Current thread the workflow is executing on 6

7 Workflows execute on a single thread from the IO thread pool at a time No code behind for WF 4 workflows, so no worries about concurrent access to the workflow code In WF 4.0, Activities may execute asynchronously on their own threads Manual threading or thread pool async execution 7

8 By default, activities execute on the workflow thread Synchronous execution from workflow start to end Can get pseudo-concurrency from some activities Parallel, ParallelForEach Some activities can now use the WF 4 async activity model i.e. InvokeMethod Allows other activites to execute concurrently in the workflow Can easily write custom async activites 8

9 AsyncCodeActivity base class BeginExecute / EndExecute overrides from the base class Instead of Execute Executed on a background thread async from the workflow thread Activity is not complete until EndExecute completes Can have multiple child activities executing on their own threads 9

10 Resources Programming.NET Components, 2 nd Edition, Juval Lowy, O Reilly & Associates Multithreading chapter MSDN WF Site: Your Feedback is Important Please fill out a session evaluation form and either put them in the basket near the exit or drop them off at the conference registration desk. Thank you! 10