8342659: Test vmTestbase/nsk/jdi/ObjectReference/referringObjects/referringObjects002/referringObjects002.java failed: Class nsk.share.jdi.TestClass1 was not unloaded

Co-authored-by: Chris Plummer <cjplummer@openjdk.org>
Reviewed-by: sspitsyn, cjplummer

Author: albertnetymk

test/hotspot/jtreg/vmTestbase/nsk/share/ClassUnloader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -28,7 +28,7 @@
 
 package nsk.share;
 
-import java.lang.ref.Cleaner;
+import java.lang.ref.PhantomReference;
 import java.util.*;
 import nsk.share.gc.gp.*;
 import nsk.share.test.ExecutionController;
@@ -77,19 +77,9 @@ public class ClassUnloader {
     public static final String INTERNAL_CLASS_LOADER_NAME = "nsk.share.CustomClassLoader";
 
     /**
-     * Whole amount of time in milliseconds to wait for class loader to be reclaimed.
+     * Phantom reference to the class loader.
      */
-    private static final int WAIT_TIMEOUT = 15000;
-
-    /**
-     * Sleep time in milliseconds for the loop waiting for the class loader to be reclaimed.
-     */
-    private static final int WAIT_DELTA = 1000;
-
-    /**
-     * Has class loader been reclaimed or not.
-     */
-    volatile boolean is_reclaimed = false;
+    private PhantomReference<Object> customClassLoaderPhantomRef = null;
 
     /**
      * Current class loader used for loading classes.
@@ -101,6 +91,14 @@ public class ClassUnloader {
      */
     private Vector<Class<?>> classObjects = new Vector<Class<?>>();
 
+    /**
+     * Has class loader been reclaimed or not.
+     */
+    private boolean isClassLoaderReclaimed() {
+        return customClassLoaderPhantomRef != null
+            && customClassLoaderPhantomRef.refersTo(null);
+    }
+
     /**
      * Class object of the first class been loaded with current class loader.
      * To get the rest loaded classes use <code>getLoadedClass(int)</code>.
@@ -138,8 +136,7 @@ public CustomClassLoader createClassLoader() {
         customClassLoader = new CustomClassLoader();
         classObjects.removeAllElements();
 
-        // Register a Cleaner to inform us when the class loader has been reclaimed.
-        Cleaner.create().register(customClassLoader, () -> { is_reclaimed = true; } );
+        customClassLoaderPhantomRef = new PhantomReference<>(customClassLoader, null);
 
         return customClassLoader;
     }
@@ -154,8 +151,7 @@ public void setClassLoader(CustomClassLoader customClassLoader) {
         this.customClassLoader = customClassLoader;
         classObjects.removeAllElements();
 
-        // Register a Cleaner to inform us when the class loader has been reclaimed.
-        Cleaner.create().register(customClassLoader, () -> { is_reclaimed = true; } );
+        customClassLoaderPhantomRef = new PhantomReference<>(customClassLoader, null);
     }
 
     /**
@@ -244,32 +240,15 @@ public void loadClass(String className, String classDir) throws ClassNotFoundExc
      */
     public boolean unloadClass(ExecutionController stresser) {
 
-        is_reclaimed = false;
-
         // free references to class and class loader to be able for collecting by GC
-        long waitTimeout = (customClassLoader == null) ? 0 : WAIT_TIMEOUT;
         classObjects.removeAllElements();
         customClassLoader = null;
 
         // force class unloading by eating memory pool
         eatMemory(stresser);
 
-        // give GC chance to run and wait for receiving reclaim notification
-        long timeToFinish = System.currentTimeMillis() + waitTimeout;
-        while (!is_reclaimed && System.currentTimeMillis() < timeToFinish) {
-            if (!stresser.continueExecution()) {
-                return false;
-            }
-            try {
-                // suspend thread for a while
-                Thread.sleep(WAIT_DELTA);
-            } catch (InterruptedException e) {
-                throw new Failure("Unexpected InterruptedException while class unloading: " + e);
-            }
-        }
-
         // force GC to unload marked class loader and its classes
-        if (is_reclaimed) {
+        if (isClassLoaderReclaimed()) {
             Runtime.getRuntime().gc();
             return true;
         }

test/hotspot/jtreg/vmTestbase/nsk/share/jpda/AbstractDebuggeeTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2006, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2006, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -149,19 +149,11 @@ public void loadTestClass(String className) {
         }
     }
 
-    public static final int MAX_UNLOAD_ATTEMPS = 5;
-
     public void unloadTestClass(String className, boolean expectedUnloadingResult) {
         ClassUnloader classUnloader = loadedClasses.get(className);
 
-        int unloadAttemps = 0;
-
         if (classUnloader != null) {
-            boolean wasUnloaded = false;
-
-            while (!wasUnloaded && (unloadAttemps++ < MAX_UNLOAD_ATTEMPS)) {
-                wasUnloaded = classUnloader.unloadClass();
-            }
+            boolean wasUnloaded = classUnloader.unloadClass();
 
             if (wasUnloaded)
                 loadedClasses.remove(className);