test/runtime/ClassUnload/UnloadTest.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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 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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/*
 * @test UnloadTest
 * @library /runtime/testlibrary /testlibrary /testlibrary/whitebox
 * @library classes
 * @build ClassUnloadCommon test.Empty
 * @build UnloadTest
 * @run main ClassFileInstaller sun.hotspot.WhiteBox
 * @run main/othervm -Xbootclasspath/a:. -Xmn8m -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI UnloadTest
 */
import sun.hotspot.WhiteBox;

/**
 * Test that verifies that classes are unloaded when they are no longer reachable.
 *
 * The test creates a class loader, uses the loader to load a class and creates an instance
 * of that class. The it nulls out all the references to the instance, class and class loader
 * and tries to trigger class unloading. Then it verifies that the class is no longer
 * loaded by the VM.
 */
public class UnloadTest {
    private static String className = "test.Empty";

    public static void main(String... args) throws Exception {
       run();
    }

    private static void run() throws Exception {
        final WhiteBox wb = WhiteBox.getWhiteBox();

        ClassUnloadCommon.failIf(wb.isClassAlive(className), "is not expected to be alive yet");

        ClassLoader cl = ClassUnloadCommon.newClassLoader();
        Class<?> c = cl.loadClass(className);
        Object o = c.newInstance();

        ClassUnloadCommon.failIf(!wb.isClassAlive(className), "should be live here");

        cl = null; c = null; o = null;
        ClassUnloadCommon.triggerUnloading();
        ClassUnloadCommon.failIf(wb.isClassAlive(className), "should have been unloaded");
    }
}