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Java example source code file (AbstractFutureFallbackAtomicHelperTest.java)

This example Java source code file (AbstractFutureFallbackAtomicHelperTest.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

abstractfuturefallbackatomichelpertest, class, classloader, classnotfoundexception, dave, exception, i'm, net, network, override, reflection, set, string, testcase, testsuite, unsafeatomichelper, urlclassloader, util

The AbstractFutureFallbackAtomicHelperTest.java Java example source code

/*
 * Copyright (C) 2015 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.util.concurrent;

import com.google.common.collect.ImmutableSet;

import junit.framework.TestCase;
import junit.framework.TestSuite;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.net.URLClassLoader;
import java.util.Set;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;

/**
 * Tests our AtomicHelper fallback strategies in AbstractFuture.
 *
 * <p>On different platforms AbstractFuture uses different strategies for its core synchronization
 * primitives.  The strategies are all implemented as subtypes of AtomicHelper and the strategy is
 * selected in the static initializer of AbstractFuture.  This is convenient and performant but
 * introduces some testing difficulties.   This test exercises the two fallback strategies in
 * abstract future.
 * <ul>
 *     <li>SafeAtomicHelper: uses AtomicReferenceFieldsUpdaters to implement synchronization
 *     <li>SynchronizedHelper: uses {@code synchronized} blocks for synchronization
 * </ul>
 *
 * To force selection of our fallback strategies we load {@link AbstractFuture} (and all of
 * {@code com.google.common.util.concurrent} in degenerate class loaders which make certain platform
 * classes unavailable.  Then we construct a test suite so we can run the normal AbstractFutureTest
 * test methods in these degenerate classloaders.
 */

public class AbstractFutureFallbackAtomicHelperTest extends TestCase {

  // stash these in static fields to avoid loading them over and over again (speeds up test
  // execution significantly)

  /**
   * This classloader blacklists sun.misc.Unsafe which will prevent us from selecting our preferred
   * strategy {@code UnsafeAtomicHelper}.
   */
  private static final ClassLoader NO_UNSAFE =
      getClassLoader(ImmutableSet.of(sun.misc.Unsafe.class.getName()));

  /**
   * This classloader blacklists sun.misc.Unsafe and AtomicReferenceFieldUpdater which will prevent
   * us from selecting our {@code SafeAtomicHelper} strategy.
   */
  private static final ClassLoader NO_ATOMIC_REFERENCE_FIELD_UPDATER =
      getClassLoader(
          ImmutableSet.of(
              sun.misc.Unsafe.class.getName(), AtomicReferenceFieldUpdater.class.getName()));

  public static TestSuite suite() {
    // we create a test suite containing a test for every AbstractFutureTest test method and we
    // set it as the name of the test.  Then in runTest we can reflectively load and invoke the
    // corresponding method on AbstractFutureTest in the correct classloader.
    TestSuite suite = new TestSuite(AbstractFutureFallbackAtomicHelperTest.class.getName());
    for (Method method : AbstractFutureTest.class.getDeclaredMethods()) {
      if (Modifier.isPublic(method.getModifiers()) && method.getName().startsWith("test")) {
        suite.addTest(
            TestSuite.createTest(AbstractFutureFallbackAtomicHelperTest.class, method.getName()));
      }
    }
    return suite;
  }

  @Override
  public void runTest() throws Exception {
    // First ensure that our classloaders are intializing the correct helper versions
    checkHelperVersion(getClass().getClassLoader(), "UnsafeAtomicHelper");
    checkHelperVersion(NO_UNSAFE, "SafeAtomicHelper");
    checkHelperVersion(NO_ATOMIC_REFERENCE_FIELD_UPDATER, "SynchronizedHelper");

    // Run the corresponding AbstractFutureTest test method in a new classloader that blacklists
    // certain core jdk classes.
    ClassLoader oldClassLoader = Thread.currentThread().getContextClassLoader();
    Thread.currentThread().setContextClassLoader(NO_UNSAFE);
    try {
      runTestMethod(NO_UNSAFE);
    } finally {
      Thread.currentThread().setContextClassLoader(oldClassLoader);
    }

    Thread.currentThread().setContextClassLoader(NO_ATOMIC_REFERENCE_FIELD_UPDATER);
    try {
      runTestMethod(NO_ATOMIC_REFERENCE_FIELD_UPDATER);
      // TODO(lukes): assert that the logs are full of errors
    } finally {
      Thread.currentThread().setContextClassLoader(oldClassLoader);
    }
  }

  private void runTestMethod(ClassLoader classLoader) throws Exception {
    Class<?> test = classLoader.loadClass(AbstractFutureTest.class.getName());
    test.getMethod(getName()).invoke(test.newInstance());
  }

  private void checkHelperVersion(ClassLoader classLoader, String expectedHelperClassName)
      throws Exception {
    // Make sure we are actually running with the expected helper implementation
    Class<?> abstractFutureClass = classLoader.loadClass(AbstractFuture.class.getName());
    Field helperField = abstractFutureClass.getDeclaredField("ATOMIC_HELPER");
    helperField.setAccessible(true);
    assertEquals(expectedHelperClassName, helperField.get(null).getClass().getSimpleName());
  }

  private static ClassLoader getClassLoader(final Set<String> blacklist) {
    final String concurrentPackage = SettableFuture.class.getPackage().getName();
    ClassLoader classLoader = AbstractFutureFallbackAtomicHelperTest.class.getClassLoader();
    return
    // we delegate to the current classloader so both loaders agree on classes like TestCase
    new URLClassLoader(((URLClassLoader) classLoader).getURLs(), classLoader) {
      @Override
      public Class<?> loadClass(String name) throws ClassNotFoundException {
        if (blacklist.contains(name)) {
          throw new ClassNotFoundException("I'm sorry Dave, I'm afraid I can't do that.");
        }
        if (name.startsWith(concurrentPackage)) {
          Class<?> c = findLoadedClass(name);
          if (c == null) {
            return super.findClass(name);
          }
          return c;
        }
        return super.loadClass(name);
      }
    };
  }
}

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