Kepler

I think is caused by one of these changes:

2012-08-23 21:43 eal

• [r64468] /trunk/diva/canvas/interactor/BasicGrabHandle.java:
  Removed overly aggressive prevention of NPE that also prevented a
  legitimate relation from occurring.

2012-08-23 21:42 eal

• [r64467] /trunk/diva/canvas/TransformContext.java: More tightly
  targetted prevention of a non-reproducible NPE upon dragging and
  connecting ports.

I think I was wrong about what causes this, more to follow.

The problem is reproducible after this change:
2012-08-18 17:08 eal

• [r64430] /trunk/ptolemy/actor/Manager.java,
  /trunk/ptolemy/actor/lib/hoc/LifeCycleManager.java,
  /trunk/ptolemy/kernel/undo/RedoChangeRequest.java,
  /trunk/ptolemy/kernel/undo/UndoChangeRequest.java,
  /trunk/ptolemy/kernel/util/Changeable.java,
  /trunk/ptolemy/kernel/util/NamedObj.java,
  /trunk/ptolemy/moml/MoMLParser.java: Fixed long standing deadlock
  that occurs while editing models while they run

Edward and I spent some time last week trying to reproduce the problem,
but could not.

I can reproduce the problem by deleting the Display or the Const.

Fixed by Edward:

I've checked in a change that I hope fixes the problem we were
chasing today. The cause is interesting...

When we edit a model, the editor constructs a MoML string for
the edit actions. E.g., to remove a Display actor, it says:

<deleteEntity name="Display"/>

It passes this string to a MoMLChangeRequest, and calls
requestChange() to request that the change be executed.

If the model is not running, then the change request will
be executed immediately within the requestChange() method.

However, executing a change request may result in additional
changes being requested... E.g., an additional change may
be requested to remove a relation.

Before my checkin, that second change request was NOT being
executed immediately. It would just sit in a queue until
it was time execute another change request (e.g., move an
actor).

The new code in NamedObj is now also simpler:

public void requestChange(ChangeRequest change) {
        NamedObj container = getContainer();

if (container != null) {
            container.requestChange(change);
        } else {
            // Synchronize to make sure we don't modify
            // the list of change requests while some other
            // thread is also trying to read or modify it.
            synchronized (_changeLock) {
                // Queue the request.
                // Create the list of requests if it doesn't already exist
                if (_changeRequests == null) {
                    _changeRequests = new LinkedList<ChangeRequest>();
                }

_changeRequests.add(change);
            }
            if (!_deferChangeRequests) {
                executeChangeRequests();
            }
        }
    }

Original Bugzilla ID was 5703