How to save the Eclipse UI (workbench state) when YOU like

At yesterday's Portland BarCamp Meetup, I was confronted with an interesting problem: David's Eclipse hangs / crashes frequently (probably that pesky PermGen issue) and when that happens the state of the Workbench is lost (i.e. which editors, views, windows are open) as it is only saved on shutdown. So we wrote a plug-in that periodically saves the UI state.

Download the plug-in here (source code here). Eclipse 3.3 only!

Here is what we did:

1. Since the UI state is saved when Eclipse shutdowns cleanly, we started by looking at the QuitAction. From here we went on to PlatformUI.getWorkbench().close(). A bit of exploration revealed that we need the methods in the snippet below.
   

   // org.eclipse.ui.internal.Workbench
   XMLMemento memento
     = XMLMemento.createWriteRoot( IWorkbenchConstants.TAG_WORKBENCH );
   saveState( memento );
   saveMementoToFile( memento )
   

   
   
2. As this code is internal, we copied it into an action which we added to the coolbar. Clicking on the "lock" icon will save the state of the workbench. BTW copying internal code can come back and bite you, but we ignored that in this case.
   
   
   
   
3. Then we made the plug-in save the UI state automatically. We added an IResourceChangeListener that is notified on POST_BUILD events. BTW this does not depend on the "auto-build" setting. Our listener will save the workbench state every 5 minutes. The help topic "Tracking Resource Changes" has more details. The listener is installed / removed in the plug-in activator:
   
   

   public void start( BundleContext context ) throws Exception {
     super.start( context );
     // ...
     rcListener = new ResourceChangeListener();
     IWorkspace workspace = ResourcesPlugin.getWorkspace();
     workspace.addResourceChangeListener(
       rcListener,
       IResourceChangeEvent.POST_BUILD );
   }
   

   
   
4. To make sure the plug-in is activated on start-up, we added a dummy contribution to the org.eclipse.ui.startup extension point.
   
   
5. If you want to monitor the plug-in's activities on the console, you can do that through a tracing option. Copy the following lines into a file called .options, place it in your eclipse directory and launch eclipse -debug
   

   # file .options in eclipse directory
   example.saveuistate/debug = true
   

   After doing a build you should see some output like this:
   
   Fri Sep 28 08:54:17 PDT 2007 Starting example.saveuistate
   Fri Sep 28 08:54:30 PDT 2007 POST_BUILD resource change
   Fri Sep 28 08:54:30 PDT 2007 Saving state.

Happy hacking,
Elias.

Image: (c) Copyright 2007, table/photocase.