Fix race condition in RCPTestWorkbenchAdvisor with CountDownLatch synchronization

The flaky test was caused by a race condition in RCPTestWorkbenchAdvisor.java.
The test spawns 4 background threads during preStartup() that schedule async/sync
runnables on the display. However, there was no guarantee these runnables would
execute before postStartup() marked the workbench as "started" (by setting
started = true). This meant asyncWithDisplayAccess could still be null when
the test assertions ran, causing intermittent failures.

This change adds a CountDownLatch to ensure all 4 async/sync operations complete
before marking the workbench as started.

Key changes to RCPTestWorkbenchAdvisor.java:
- Added CountDownLatch field initialized as a constant with count of 4
- Added proper imports for CountDownLatch and TimeUnit
- Simplified Boolean assignments to use !isSTARTED() directly
- Added finally blocks in setupSyncDisplayThread() and setupAsyncDisplayThread()
  to call asyncLatch.countDown()
- Modified postStartup() to await latch completion with 5-second timeout
- Replaced warning logs with AssertionError on timeout and RuntimeException
  on interruption to ensure test failures are explicit

Also bumps version of org.eclipse.ui.tests.harness for 4.38 stream.

Fixes #1517

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: vogella

tests/org.eclipse.ui.tests.harness/META-INF/MANIFEST.MF

@@ -2,7 +2,7 @@ Manifest-Version: 1.0
 Bundle-ManifestVersion: 2
 Bundle-Name: Harness Plug-in
 Bundle-SymbolicName: org.eclipse.ui.tests.harness;singleton:=true
-Bundle-Version: 1.10.600.qualifier
+Bundle-Version: 1.10.700.qualifier
 Eclipse-BundleShape: dir
 Require-Bundle: org.eclipse.ui,
  org.eclipse.core.runtime,

tests/org.eclipse.ui.tests.harness/src/org/eclipse/ui/tests/harness/util/RCPTestWorkbenchAdvisor.java

@@ -13,6 +13,9 @@
  *******************************************************************************/
 package org.eclipse.ui.tests.harness.util;
 
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
 import org.eclipse.jface.preference.IPreferenceStore;
 import org.eclipse.swt.SWTException;
 import org.eclipse.swt.widgets.Display;
@@ -44,6 +47,9 @@ public class RCPTestWorkbenchAdvisor extends WorkbenchAdvisor {
 
 	private static boolean started = false;
 
+	// Use a CountDownLatch to ensure async operations complete before postStartup
+	private static final CountDownLatch asyncLatch = new CountDownLatch(4);
+
 	public static boolean isSTARTED() {
 		synchronized (RCPTestWorkbenchAdvisor.class) {
 			return started;
@@ -122,12 +128,10 @@ public void eventLoopIdle(final Display display) {
 	public void preStartup() {
 		super.preStartup();
 		final Display display = Display.getCurrent();
+
 		if (display != null) {
 			display.asyncExec(() -> {
-				if (isSTARTED())
-					asyncDuringStartup = Boolean.FALSE;
-				else
-					asyncDuringStartup = Boolean.TRUE;
+				asyncDuringStartup = !isSTARTED();
 			});
 		}
 
@@ -160,15 +164,18 @@ public void run() {
 					display.syncExec(() -> {
 						synchronized (RCPTestWorkbenchAdvisor.class) {
 							if (callDisplayAccess)
-								syncWithDisplayAccess = !isSTARTED() ? Boolean.TRUE : Boolean.FALSE;
+								syncWithDisplayAccess = !isSTARTED();
 							else
-								syncWithoutDisplayAccess = !isSTARTED() ? Boolean.TRUE : Boolean.FALSE;
+								syncWithoutDisplayAccess = !isSTARTED();
 						}
 					});
 				} catch (SWTException e) {
 					// this can happen because we shut down the workbench just
 					// as soon as we're initialized - ie: when we're trying to
 					// run this runnable in the deferred case.
+				} finally {
+					// Signal that this operation has completed
+					asyncLatch.countDown();
 				}
 			}
 		};
@@ -183,11 +190,16 @@ public void run() {
 				if (callDisplayAccess)
 					DisplayAccess.accessDisplayDuringStartup();
 				display.asyncExec(() -> {
-					synchronized (RCPTestWorkbenchAdvisor.class) {
-						if (callDisplayAccess)
-							asyncWithDisplayAccess = !isSTARTED() ? Boolean.TRUE : Boolean.FALSE;
-						else
-							asyncWithoutDisplayAccess = !isSTARTED() ? Boolean.TRUE : Boolean.FALSE;
+					try {
+						synchronized (RCPTestWorkbenchAdvisor.class) {
+							if (callDisplayAccess)
+								asyncWithDisplayAccess = !isSTARTED();
+							else
+								asyncWithoutDisplayAccess = !isSTARTED();
+						}
+					} finally {
+						// Signal that this operation has completed
+						asyncLatch.countDown();
 					}
 				});
 			}
@@ -199,6 +211,20 @@ public void run() {
 	@Override
 	public void postStartup() {
 		super.postStartup();
+
+		// Wait for all async/sync operations to complete before marking as started
+		// This prevents a race condition where asyncWithDisplayAccess might not be set yet
+		try {
+			// Wait up to 5 seconds for all operations to complete
+			boolean completed = asyncLatch.await(5, TimeUnit.SECONDS);
+			if (!completed) {
+				throw new AssertionError("Not all async/sync operations completed within timeout");
+			}
+		} catch (InterruptedException e) {
+			Thread.currentThread().interrupt();
+			throw new RuntimeException("Interrupted while waiting for async/sync operations", e);
+		}
+
 		synchronized (RCPTestWorkbenchAdvisor.class) {
 			started = true;
 		}