8311989: Test java/lang/Thread/virtual/Reflection.java timed out

Backport-of: 6faf05c6ddb3a0bcf4dce9516b8fca15d25cd80f

test/jdk/java/lang/Thread/virtual/Reflection.java

@@ -32,6 +32,7 @@
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
+import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ThreadFactory;
@@ -146,15 +147,19 @@ void testInvokeStatic6() throws Exception {
         try (ExecutorService scheduler = Executors.newFixedThreadPool(1)) {
             Thread.Builder builder = ThreadBuilders.virtualThreadBuilder(scheduler);
             ThreadFactory factory = builder.factory();
+
+            var ready = new CountDownLatch(1);
             Thread vthread = factory.newThread(() -> {
+                ready.countDown();
                 try {
                     parkMethod.invoke(null);   // blocks
                 } catch (Exception e) { }
             });
             vthread.start();
+
             try {
-                // give thread time to be scheduled
-                Thread.sleep(100);
+                // wait for thread to run
+                ready.await();
 
                 // unpark with another virtual thread, runs on same carrier thread
                 Thread unparker = factory.newThread(() -> LockSupport.unpark(vthread));
@@ -321,17 +326,27 @@ void testNewInstance6() throws Exception {
         try (ExecutorService scheduler = Executors.newFixedThreadPool(1)) {
             Thread.Builder builder = ThreadBuilders.virtualThreadBuilder(scheduler);
             ThreadFactory factory = builder.factory();
+
+            var ready = new CountDownLatch(1);
             Thread vthread = factory.newThread(() -> {
+                ready.countDown();
                 try {
                     ctor.newInstance();
                 } catch (Exception e) { }
             });
             vthread.start();
 
-            Thread.sleep(100); // give thread time to be scheduled
+            try {
+                // wait for thread to run
+                ready.await();
 
-            // unpark with another virtual thread, runs on same carrier thread
-            factory.newThread(() -> LockSupport.unpark(vthread)).start();
+                // unpark with another virtual thread, runs on same carrier thread
+                Thread unparker = factory.newThread(() -> LockSupport.unpark(vthread));
+                unparker.start();
+                unparker.join();
+            } finally {
+                LockSupport.unpark(vthread);  // in case test fails
+            }
         }
     }