Added IHandleAsync, these handlers will be run async and in parallel to each other.

NzbDrone.Common/Eventing/IHandle.cs

@@ -9,14 +9,32 @@ namespace NzbDrone.Common.Eventing
     public interface IHandle<TEvent> : IHandle where TEvent : IEvent
     {
         /// <summary>
-        ///   Handles the message.
+        ///   Handles the message synchronously.
         /// </summary>
         /// <param name = "message">The message.</param>
         void Handle(TEvent message);
     }
 
+    /// <summary>
+    ///   Denotes a class which can handle a particular type of message.
+    /// </summary>
+    /// <typeparam name = "TEvent">The type of message to handle.</typeparam>
+    public interface IHandleAsync<TEvent> : IHandleAsync where TEvent : IEvent
+    {
+        /// <summary>
+        ///   Handles the message asynchronously.
+        /// </summary>
+        /// <param name = "message">The message.</param>
+        void HandleAsync(TEvent message);
+    }
+
     /// <summary>
     ///   A marker interface for classes that subscribe to messages.
     /// </summary>
     public interface IHandle { }
+
+    /// <summary>
+    ///   A marker interface for classes that subscribe to messages.
+    /// </summary>
+    public interface IHandleAsync : IHandle { }
 }