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/*
* @test
* @summary verify if the hidden class is unloaded when the class loader is GC'ed
* @modules jdk.compiler
* @library /test/lib/
* @build jdk.test.lib.util.ForceGC
* @run testng/othervm UnloadingTest
*/
import java.io.IOException;
import java.lang.invoke.MethodHandles.Lookup;
import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.concurrent.atomic.AtomicInteger;
import jdk.test.lib.util.ForceGC;
import jdk.test.lib.compiler.CompilerUtils;
import jdk.test.lib.Utils;
import org.testng.annotations.BeforeTest;
import org.testng.annotations.Test;
import static java.lang.invoke.MethodHandles.lookup;
import static java.lang.invoke.MethodHandles.Lookup.ClassOption.*;
import static org.testng.Assert.*;
public class UnloadingTest {
private static final Path CLASSES_DIR = Paths.get("classes");
private static byte[] hiddenClassBytes;
@BeforeTest
static void setup() throws IOException {
Path src = Paths.get(Utils.TEST_SRC, "src", "LookupHelper.java");
if (!CompilerUtils.compile(src, CLASSES_DIR)) {
throw new RuntimeException("Compilation of the test failed: " + src);
}
hiddenClassBytes = Files.readAllBytes(CLASSES_DIR.resolve("LookupHelper.class"));
}
/*
* Test that a hidden class is unloaded while the loader remains strongly reachable
*/
@Test
public void unloadable() throws Exception {
TestLoader loader = new TestLoader();
Class<?> helper = Class.forName("LookupHelper", true, loader);
Method m = helper.getMethod("getLookup");
Lookup lookup = (Lookup)m.invoke(null);
HiddenClassUnloader unloader = createHiddenClass(lookup, false);
// the hidden class should be unloaded
unloader.unload();
// loader is strongly reachable
Reference.reachabilityFence(loader);
}
/*
* Test that a hidden class is not unloaded when the loader is strongly reachable
*/
@Test
public void notUnloadable() throws Exception {
TestLoader loader = new TestLoader();
Class<?> helper = Class.forName("LookupHelper", true, loader);
Method m = helper.getMethod("getLookup");
Lookup lookup = (Lookup)m.invoke(null);
HiddenClassUnloader unloader = createHiddenClass(lookup, true);
assertFalse(unloader.tryUnload()); // hidden class is not unloaded
// loader is strongly reachable
Reference.reachabilityFence(loader);
}
/*
* Create a nest of two hidden classes.
* They can be unloaded even the loader is strongly reachable
*/
@Test
public void hiddenClassNest() throws Exception {
TestLoader loader = new TestLoader();
Class<?> helper = Class.forName("LookupHelper", true, loader);
Method m = helper.getMethod("getLookup");
Lookup lookup = (Lookup)m.invoke(null);
HiddenClassUnloader[] unloaders = createNestOfTwoHiddenClasses(lookup, false, false);
// keep a strong reference to the nest member class
Class<?> member = unloaders[1].weakRef.get();
assertTrue(member != null);
// nest host and member will not be unloaded
assertFalse(unloaders[0].tryUnload());
assertFalse(unloaders[1].tryUnload());
// clear the reference to the nest member
Reference.reachabilityFence(member);
member = null;
// nest host and member will be unloaded
unloaders[0].unload();
unloaders[1].unload();
// loader is strongly reachable
Reference.reachabilityFence(loader);
}
/*
* Create a nest with a hidden class nest host and strong nest member.
* Test that both are not unloaded
*/
@Test
public void hiddenClassNestStrongMember() throws Exception {
TestLoader loader = new TestLoader();
Class<?> helper = Class.forName("LookupHelper", true, loader);
Method m = helper.getMethod("getLookup");
Lookup lookup = (Lookup)m.invoke(null);
HiddenClassUnloader[] unloaders = createNestOfTwoHiddenClasses(lookup, false, true);
assertFalse(unloaders[0].tryUnload()); // nest host cannot be unloaded
assertFalse(unloaders[1].tryUnload()); // nest member cannot be unloaded
// loader is strongly reachable
Reference.reachabilityFence(loader);
}
/*
* Create a nest with a strong hidden nest host and a hidden class member.
* The nest member can be unloaded whereas the nest host will not be unloaded.
*/
@Test
public void hiddenClassNestStrongHost() throws Exception {
TestLoader loader = new TestLoader();
Class<?> helper = Class.forName("LookupHelper", true, loader);
Method m = helper.getMethod("getLookup");
Lookup lookup = (Lookup)m.invoke(null);
HiddenClassUnloader[] unloaders = createNestOfTwoHiddenClasses(lookup, true, false);
assertFalse(unloaders[0].tryUnload()); // nest host cannot be unloaded
unloaders[1].unload();
// loader is strongly reachable
Reference.reachabilityFence(loader);
}
/*
* Create a HiddenClassUnloader that holds a weak reference to the newly created
* hidden class.
*/
static HiddenClassUnloader createHiddenClass(Lookup lookup, boolean strong) throws Exception {
Class<?> hc;
if (strong) {
hc = lookup.defineHiddenClass(hiddenClassBytes, false, STRONG).lookupClass();
} else {
hc = lookup.defineHiddenClass(hiddenClassBytes, false).lookupClass();
}
assertTrue(hc.getClassLoader() == lookup.lookupClass().getClassLoader());
return new HiddenClassUnloader(hc);
}
/*
* Create an array of HiddenClassUnloader with two elements: the first element
* is for the nest host and the second element is for the nest member.
*/
static HiddenClassUnloader[] createNestOfTwoHiddenClasses(Lookup lookup, boolean strongHost, boolean strongMember) throws Exception {
Lookup hostLookup;
if (strongHost) {
hostLookup = lookup.defineHiddenClass(hiddenClassBytes, false, STRONG);
} else {
hostLookup = lookup.defineHiddenClass(hiddenClassBytes, false);
}
Class<?> host = hostLookup.lookupClass();
Class<?> member;
if (strongMember) {
member = hostLookup.defineHiddenClass(hiddenClassBytes, false, NESTMATE, STRONG).lookupClass();
} else {
member = hostLookup.defineHiddenClass(hiddenClassBytes, false, NESTMATE).lookupClass();
}
assertTrue(member.getNestHost() == host);
return new HiddenClassUnloader[] { new HiddenClassUnloader(host), new HiddenClassUnloader(member) };
}
static class HiddenClassUnloader {
private final WeakReference<Class<?>> weakRef;
private HiddenClassUnloader(Class<?> hc) {
assertTrue(hc.isHidden());
this.weakRef = new WeakReference<>(hc);
}
void unload() {
// Force garbage collection to trigger unloading of class loader
// and native library.
if (!ForceGC.wait(() -> weakRef.refersTo(null))) {
throw new RuntimeException("loader " + " not unloaded!");
}
}
boolean tryUnload() {
return ForceGC.wait(() -> weakRef.refersTo(null));
}
}
static class TestLoader extends URLClassLoader {
static URL[] toURLs() {
try {
return new URL[] { CLASSES_DIR.toUri().toURL() };
} catch (MalformedURLException e) {
throw new Error(e);
}
}
static AtomicInteger counter = new AtomicInteger();
TestLoader() {
super("testloader-" + counter.addAndGet(1), toURLs(), ClassLoader.getSystemClassLoader());
}
}
}