KeepAliveObject.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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 * 2 along with this work; if not, write to the Free Software Foundation,
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/*
 * @test KeepAliveObject
 * @summary This test case uses a class instance to keep the class alive.
 * @library /testlibrary /testlibrary/whitebox /runtime/testlibrary
 * @library classes
 * @build KeepAliveObject test.Empty
 * @build ClassUnloadCommon
 * @run main ClassFileInstaller sun.hotspot.WhiteBox
 * @run main/othervm -Xbootclasspath/a:. -Xmn8m -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI KeepAliveObject
 */

import sun.hotspot.WhiteBox;

/**
 * Test that verifies that classes are not unloaded when specific types of references are kept to them.
 */
public class KeepAliveObject {
  private static final String className = "test.Empty";
  private static final WhiteBox wb = WhiteBox.getWhiteBox();
  public static Object escape = null;

  public static void main(String... args) throws Exception {
    ClassLoader cl = ClassUnloadCommon.newClassLoader();
    Class<?> c = cl.loadClass(className);
    Object o = c.newInstance();
    cl = null; c = null;
    escape = o;

    {
        boolean isAlive = wb.isClassAlive(className);
        System.out.println("testObject (1) alive: " + isAlive);

        ClassUnloadCommon.failIf(!isAlive, "should be alive");
    }

    ClassUnloadCommon.triggerUnloading();

    {
        boolean isAlive = wb.isClassAlive(className);
        System.out.println("testObject (2) alive: " + isAlive);

        ClassUnloadCommon.failIf(!isAlive, "should be alive");
    }
    o = null;
    escape = null;
    ClassUnloadCommon.triggerUnloading();

    {
        boolean isAlive = wb.isClassAlive(className);
        System.out.println("testObject (3) alive: " + isAlive);
        ClassUnloadCommon.failIf(isAlive, "should be unloaded");
    }

  }
}