Monday, January 3, 2011

How to implement IAsyncResult and ISynchronizeInvoke

In this post I will demonstrate how to implement a sync object using the two .net classes IAsyncResult and ISynchronizeInvoke 


IAsyncResult will be used to store the action result
ISynchronizeInvoke will be used to synchronize all access to the resource that uses the sync object


class SimpleAsyncResult : IAsyncResult {
      object _state;


      public bool IsCompleted { get; set; }


      public WaitHandle AsyncWaitHandle { get; internal set; }


      public object AsyncState {
         get {
            if (Exception != null) {
               throw Exception;
            }
            return _state;
         }
         internal set {
            _state = value;
         }
      }


      public bool CompletedSynchronously { get { return IsCompleted; } }


      internal Exception Exception { get; set; }
   }


   class SimpleSyncObject : ISynchronizeInvoke {
      private readonly object _sync;


      public SimpleSyncObject() {
         _sync = new object();
      }


      public IAsyncResult BeginInvoke(Delegate method, object[] args) {
         var result = new SimpleAsyncResult();


         ThreadPool.QueueUserWorkItem(delegate {
            result.AsyncWaitHandle = new ManualResetEvent(false);
            try {
               result.AsyncState = Invoke(method, args);
            } catch (Exception exception) {
               result.Exception = exception;
            }
            result.IsCompleted = true;
         });


         return result;
      }


      public object EndInvoke(IAsyncResult result) {
         if (!result.IsCompleted) {
            result.AsyncWaitHandle.WaitOne();
         }


         return result.AsyncState;
      }


      public object Invoke(Delegate method, object[] args) {
         lock (_sync) {
            return method.DynamicInvoke(args);
         }
      }


      public bool InvokeRequired {
         get { return true; }
      }
   }


Hope the post was helpful

2 comments:

  1. Great to know about the IAsyncResult and ISynchronizeInvoke. I used to remain confused between IAsyncResult and ISynchronizeInvoke but you explained everything in very simple language. I learned both one very easily.
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