Fix race condition in CleanupAddon.subscribeRenderingChanged

The test ensureCleanUpAddonCleansUp was failing intermittently because
CleanupAddon deferred container cleanup via Display.asyncExec(), creating
a race condition where event loop pumping during part activation could
interfere with async cleanup tasks.

Root cause analysis:
- When hidePart() is called on parts with REMOVE_ON_HIDE_TAG, it triggers
  synchronous EMF model change events via UIEventPublisher
- Event delivery is fully synchronous: EventBroker.send() ->
  EventAdmin.sendEvent() -> Display.syncExec() -> handler execution
- The subscribeRenderingChanged handler detected visCount==0 but deferred
  cleanup via asyncExec (line 352)
- Meanwhile, activate() calls during hidePart() pumped the event loop
  (via focusGui/SWT focus handling), potentially consuming queued asyncExecs
  before they could observe the final state
- This created timing-dependent behavior where cleanup could be skipped

Fix:
- Remove asyncExec wrapper from subscribeRenderingChanged's visCount==0 path
- Since event delivery is synchronous, visCount already reflects the actual
  state at event time - no need to defer and re-check
- Container is now hidden immediately when last renderable child becomes
  non-renderable, before any event loop pumping can interfere
- Update test to use simple spinEventLoop + assertFalse instead of
  30-second waitForCondition, as cleanup is now synchronous

This fixes the flaky test that failed ~1-3% of the time even with the
30-second timeout. The subscribeTopicChildren handler still uses asyncExec
for children removal/sash unwrapping, but toBeRendered cleanup is now
deterministic.

Fixes #3581

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: vogella

bundles/org.eclipse.e4.ui.workbench.addons.swt/src/org/eclipse/e4/ui/workbench/addons/cleanupaddon/CleanupAddon.java

@@ -346,16 +346,13 @@ private void subscribeRenderingChanged(
 				int visCount = modelService.countRenderableChildren(container);
 
 				// Remove stacks with no visible children from the display (but not the
-				// model)
-				final MElementContainer<MUIElement> theContainer = container;
-				if (visCount == 0) {
-					Display.getCurrent().asyncExec(() -> {
-						int visCount1 = modelService.countRenderableChildren(theContainer);
-						if (!isLastEditorStack(theContainer) && visCount1 == 0) {
-							theContainer.setToBeRendered(false);
-							transferPrimaryDataStackIfRemoved(theContainer);
-						}
-					});
+				// model). Since event delivery is synchronous (EventBroker.send via
+				// EventAdmin.sendEvent and Display.syncExec), the visCount reflects
+				// the actual state at the time of this event and can be acted upon
+				// immediately without deferring via asyncExec.
+				if (visCount == 0 && !isLastEditorStack(container)) {
+					container.setToBeRendered(false);
+					transferPrimaryDataStackIfRemoved(container);
 				} else if (container.getParent() != null) { // omit detached windows
 					// if there are rendered elements but none are 'visible' we should
 					// make the container invisible as well

tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/workbench/PartRenderingEngineTests.java

@@ -64,7 +64,6 @@
 import org.eclipse.swt.widgets.Shell;
 import org.eclipse.swt.widgets.ToolBar;
 import org.eclipse.swt.widgets.Widget;
-import org.eclipse.ui.tests.harness.util.DisplayHelper;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Disabled;
@@ -2447,12 +2446,9 @@ public void ensureCleanUpAddonCleansUp() {
 		assertTrue(partStackForPartBPartC.isToBeRendered(), " PartStack with children should be rendered");
 		partService.hidePart(partB);
 		partService.hidePart(partC);
-		// DisplayHelper.waitForCondition() handles event processing via Display.sleep()
-		// and retries. Calling spinEventLoop() here creates a race condition where
-		// events may be processed before CleanupAddon's asyncExec() is queued (line 352).
-		assertTrue(
-				DisplayHelper.waitForCondition(Display.getDefault(), 30_000,
-						() -> !partStackForPartBPartC.isToBeRendered()), "CleanupAddon should ensure that partStack is not rendered anymore, as all childs have been removed");
+		contextRule.spinEventLoop();
+		assertFalse(partStackForPartBPartC.isToBeRendered(),
+				"CleanupAddon should ensure that partStack is not rendered anymore, as all childs have been removed");
 		// PartStack with IPresentationEngine.NO_AUTO_COLLAPSE should not be removed
 		// even if children are removed
 		partService.hidePart(editor, true);