Proposal: asyncronous backends

[dave <davidr sucs org>]

Hi all,

While looking at ways to get weather info via a webservice, I noticed
that while a backend is busy (e.g. waiting for a webservice reply), the
dashboard remains locked up. This really sucks.

So, I suggest that backends get a callback mechanism so that if they
have anything to do that might take a while, they can launch a new
thread and call this function when they're done to report new / changed
results.

I've coded something up which works nicely with the weather backend and
requires only very minor changes to the dashboard/backend bits. See
attached.

With this approach, backends get a GuiMatchNotifyDelegate which they can
then call from a background thread to add a new result or to update an
existing one.

dave


--- cvs/dashboard/engine/dashboard.cs	2004-03-04 08:07:29.000000000 +0000
+++ dashboard/engine/dashboard.cs	2004-03-05 13:20:07.113082032 +0000
@@ -92,6 +92,8 @@
 
 			string [] files = Directory.GetFiles (backends_dir, "*.dll");
 
+			GuiMatchNotifyDelegate callback = new GuiMatchNotifyDelegate(this.BackendCallback);
+
 			foreach (string file in files) {
 				try {
 
@@ -105,6 +107,7 @@
 					Console.WriteLine ("Loading backend: " + file);
 
 					Backend backend = (Backend) Activator.CreateInstance (a.GetType (attr.FactoryClass));
+					backend.UpdateResultCallback = callback; // FIXME: possibly stick this in a constructor somewhere?
 
 					ThreadPool.QueueUserWorkItem (new WaitCallback (this.LaunchBackend), backend);
 				} catch {
@@ -158,7 +161,7 @@
 					if (attr == null)
 						continue;
 
-					Console.WriteLine ("Loading render: " + file);
+					Console.WriteLine ("Loading renderer: " + file);
 					MatchRenderer renderer = (MatchRenderer) Activator.CreateInstance (a.GetType (attr.FactoryClass));
 
 					ThreadPool.QueueUserWorkItem (new WaitCallback (this.LaunchRenderer), renderer);
@@ -193,6 +196,16 @@
 			}
 		}
 
+		// called by backends to update results or add new ones
+		public void BackendCallback (BackendResult result) {
+			lock (this.ems) {
+				if (result != null)
+					this.ems.AddBackendResult (result);
+
+					this.window.Display (this.ems);
+			}
+		}
+
 		//
 		// Notify the GUI to update
 		//
--- cvs/dashboard/engine/Backend.cs	2004-02-20 13:03:22.000000000 +0000
+++ dashboard/engine/Backend.cs	2004-03-05 10:44:04.006616416 +0000
@@ -23,6 +23,8 @@
 		// sent to it.
 		public abstract bool  Startup ();
 
+		public GuiMatchNotifyDelegate UpdateResultCallback;
+
 		public IList SubscribedClueTypes = null;
 
 		protected void SubscribeToClues (params string[] clue_types_supported)