Issue #14904 - Stabilize virtual thread tracking dump test

jetty-core/jetty-util/src/test/java/org/eclipse/jetty/util/thread/VirtualThreadPoolTest.java

@@ -117,16 +117,22 @@ public void testTrackingDump() throws Exception
         assertThat(trackingExecutor.size(), is(0));
 
         CountDownLatch running = new CountDownLatch(4);
-        Waiter waiter = new Waiter(running, false);
-        Waiter spinner = new Waiter(running, true);
+        CountDownLatch release = new CountDownLatch(1);
+        Waiter[] waiters =
+            {
+                new Waiter(running, release, false),
+                new Waiter(running, release, true),
+                new Waiter(running, release, false),
+                new Waiter(running, release, true)
+            };
         try
         {
-            vtp.execute(waiter);
-            vtp.execute(spinner);
-            vtp.execute(waiter);
-            vtp.execute(spinner);
+            for (Waiter waiter : waiters)
+                vtp.execute(waiter);
 
             assertTrue(running.await(5, TimeUnit.SECONDS));
+            await().atMost(5, TimeUnit.SECONDS).until(waiters[0].getThread()::getState, is(Thread.State.WAITING));
+            await().atMost(5, TimeUnit.SECONDS).until(waiters[2].getThread()::getState, is(Thread.State.WAITING));
             assertThat(trackingExecutor.size(), is(4));
 
             vtp.setDetailedDump(false);
@@ -143,11 +149,13 @@ public void testTrackingDump() throws Exception
             assertThat(count(dump, "waiting"), is(2));
             assertThat(count(dump, "VirtualThreadPoolTest.java"), is(4));
             assertThat(count(dump, "CountDownLatch.await("), is(2));
+
+            release.countDown();
+            await().atMost(5, TimeUnit.SECONDS).until(trackingExecutor::size, is(0));
         }
         finally
         {
-            waiter.countDown();
-            spinner.countDown();
+            release.countDown();
             vtp.stop();
         }
     }
@@ -209,28 +217,35 @@ public static int count(String str, String subStr)
         return count;
     }
 
-    private static class Waiter extends CountDownLatch implements Runnable
+    private static class Waiter implements Runnable
     {
         private final CountDownLatch _running;
+        private final CountDownLatch _release;
         private final boolean _spin;
+        private Thread _thread;
 
-        public Waiter(CountDownLatch running, boolean spin)
+        public Waiter(CountDownLatch running, CountDownLatch release, boolean spin)
         {
-            super(1);
             _running = running;
+            _release = release;
             _spin = spin;
         }
 
+        public Thread getThread()
+        {
+            return _thread;
+        }
+
         @Override
         public void run()
         {
             try
             {
+                _thread = Thread.currentThread();
                 _running.countDown();
-                while (_spin && getCount() > 0)
+                while (_spin && _release.getCount() > 0)
                     Thread.onSpinWait();
-                if (!await(10, TimeUnit.SECONDS))
-                    throw new IllegalStateException();
+                _release.await();
             }
             catch (InterruptedException e)
             {