Google-Guava Concurrent包里的Service框架浅析

原文地址译文地址译者：何一昕校对：方腾飞

概述

Guava包里的Service接口用于封装一个服务对象的运行状态、包括start和stop等方法。例如web服务器，RPC服务器、计时器等可以实现这个接口。对此类服务的状态管理并不轻松、需要对服务的开启/关闭进行妥善管理、特别是在多线程环境下尤为复杂。Guava包提供了一些基础类帮助你管理复杂的状态转换逻辑和同步细节。

使用一个服务

一个服务正常生命周期有：

服务一旦被停止就无法再重新启动了。如果服务在starting、running、stopping状态出现问题、会进入Service.State.FAILED.状态。调用 startAsync()方法可以异步开启一个服务,同时返回this对象形成方法调用链。注意：只有在当前服务的状态是NEW时才能调用startAsync()方法，因此最好在应用中有一个统一的地方初始化相关服务。停止一个服务也是类似的、使用异步方法stopAsync() 。但是不像startAsync(),多次调用这个方法是安全的。这是为了方便处理关闭服务时候的锁竞争问题。

Service也提供了一些方法用于等待服务状态转换的完成:

通过 addListener()方法异步添加监听器。此方法允许你添加一个 Service.Listener 、它会在每次服务状态转换的时候被调用。注意：最好在服务启动之前添加Listener（这时的状态是NEW）、否则之前已发生的状态转换事件是无法在新添加的Listener上被重新触发的。

同步使用awaitRunning()。这个方法不能被打断、不强制捕获异常、一旦服务启动就会返回。如果服务没有成功启动，会抛出IllegalStateException异常。同样的， awaitTerminated() 方法会等待服务达到终止状态（TERMINATED 或者 FAILED）。两个方法都有重载方法允许传入超时时间。

Service 接口本身实现起来会比较复杂、且容易碰到一些捉摸不透的问题。因此我们不推荐直接实现这个接口。而是请继承Guava包里已经封装好的基础抽象类。每个基础类支持一种特定的线程模型。

基础实现类

AbstractIdleService

AbstractIdleService 类简单实现了Service接口、其在running状态时不会执行任何动作–因此在running时也不需要启动线程–但需要处理开启/关闭动作。要实现一个此类的服务，只需继承AbstractIdleService类，然后自己实现startUp() 和shutDown()方法就可以了。

  protected void startUp() {
  servlets.add(new GcStatsServlet());
  }
  protected void shutDown() {}

如上面的例子、由于任何请求到GcStatsServlet时已经会有现成线程处理了，所以在服务运行时就不需要做什么额外动作了。

AbstractExecutionThreadService

AbstractExecutionThreadService 通过单线程处理启动、运行、和关闭等操作。你必须重载run()方法，同时需要能响应停止服务的请求。具体的实现可以在一个循环内做处理：

  public void run() {
    while (isRunning()) {
      // perform a unit of work
    }
  }

另外，你还可以重载triggerShutdown()方法让run()方法结束返回。

重载startUp()和shutDown()方法是可选的，不影响服务本身状态的管理

01    protected void startUp() {
02    dispatcher.listenForConnections(port, queue);
03     }
04     protected void run() {
05       Connection connection;
06       while ((connection = queue.take() != POISON)) {
07         process(connection);
08       }
09     }
10     protected void triggerShutdown() {
11       dispatcher.stopListeningForConnections(queue);
12       queue.put(POISON);
13     }

start()内部会调用startUp()方法，创建一个线程、然后在线程内调用run()方法。stop()会调用 triggerShutdown()方法并且等待线程终止。

AbstractScheduledService

AbstractScheduledService类用于在运行时处理一些周期性的任务。子类可以实现 runOneIteration()方法定义一个周期执行的任务，以及相应的startUp()和shutDown()方法。为了能够描述执行周期，你需要实现scheduler()方法。通常情况下，你可以使用AbstractScheduledService.Scheduler类提供的两种调度器：newFixedRateSchedule(initialDelay, delay, TimeUnit) 和newFixedDelaySchedule(initialDelay, delay, TimeUnit)，类似于JDK并发包中ScheduledExecutorService类提供的两种调度方式。如要自定义schedules则可以使用 CustomScheduler类来辅助实现；具体用法见javadoc。

AbstractService

如需要自定义的线程管理、可以通过扩展 AbstractService类来实现。一般情况下、使用上面的几个实现类就已经满足需求了，但如果在服务执行过程中有一些特定的线程处理需求、则建议继承AbstractService类。

继承AbstractService方法必须实现两个方法.

doStart(): 首次调用startAsync()时会同时调用doStart(),doStart()内部需要处理所有的初始化工作、如果启动成功则调用notifyStarted()方法；启动失败则调用notifyFailed()
doStop(): 首次调用stopAsync()会同时调用doStop(),doStop()要做的事情就是停止服务，如果停止成功则调用 notifyStopped()方法；停止失败则调用 notifyFailed()方法。

doStart和doStop方法的实现需要考虑下性能，尽可能的低延迟。如果初始化的开销较大，如读文件，打开网络连接，或者其他任何可能引起阻塞的操作，建议移到另外一个单独的线程去处理。

使用ServiceManager

除了对Service接口提供基础的实现类，Guava还提供了 ServiceManager类使得涉及到多个Service集合的操作更加容易。通过实例化ServiceManager类来创建一个Service集合，你可以通过以下方法来管理它们：

startAsync() ：将启动所有被管理的服务。如果当前服务的状态都是NEW的话、那么你只能调用该方法一次、这跟 Service#startAsync()是一样的。
stopAsync() ：将停止所有被管理的服务。
addListener ：会添加一个ServiceManager.Listener，在服务状态转换中会调用该Listener
awaitHealthy() ：会等待所有的服务达到Running状态
awaitStopped()：会等待所有服务达到终止状态

检测类的方法有：

isHealthy() ：如果所有的服务处于Running状态、会返回True
servicesByState()：以状态为索引返回当前所有服务的快照
startupTimes() ：返回一个Map对象，记录被管理的服务启动的耗时、以毫秒为单位，同时Map默认按启动时间排序。

我们建议整个服务的生命周期都能通过ServiceManager来管理，不过即使状态转换是通过其他机制触发的、也不影响ServiceManager方法的正确执行。例如：当一个服务不是通过startAsync()、而是其他机制启动时，listeners 仍然可以被正常调用、awaitHealthy()也能够正常工作。ServiceManager 唯一强制的要求是当其被创建时所有的服务必须处于New状态。

附：TestCase、也可以作为练习Demo

ServiceTest

  </pre>
  /*
   * Copyright (C) 2013 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 static com.google.common.util.concurrent.Service.State.FAILED;
  import static com.google.common.util.concurrent.Service.State.NEW;
  import static com.google.common.util.concurrent.Service.State.RUNNING;
  import static com.google.common.util.concurrent.Service.State.STARTING;
  import static com.google.common.util.concurrent.Service.State.STOPPING;
  import static com.google.common.util.concurrent.Service.State.TERMINATED;
   
  import junit.framework.TestCase;
   
  /**
   * Unit tests for {@link Service}
   */
  public class ServiceTest extends TestCase {
   
  /** Assert on the comparison ordering of the State enum since we guarantee it. */
   public void testStateOrdering() {
   // List every valid (direct) state transition.
   assertLessThan(NEW, STARTING);
   assertLessThan(NEW, TERMINATED);
   
   assertLessThan(STARTING, RUNNING);
   assertLessThan(STARTING, STOPPING);
   assertLessThan(STARTING, FAILED);
   
   assertLessThan(RUNNING, STOPPING);
   assertLessThan(RUNNING, FAILED);
   
   assertLessThan(STOPPING, FAILED);
   assertLessThan(STOPPING, TERMINATED);
   }
   
   private static <T extends Comparable<? super T>> void assertLessThan(T a, T b) {
   if (a.compareTo(b) >= 0) {
   fail(String.format("Expected %s to be less than %s", a, b));
   }
   }
  }
  <pre>
AbstractIdleServiceTest

  /*
   * Copyright (C) 2009 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 static org.truth0.Truth.ASSERT;
   
  import com.google.common.collect.Lists;
   
  import junit.framework.TestCase;
   
  import java.util.List;
  import java.util.concurrent.Executor;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
   
  /**
   * Tests for {@link AbstractIdleService}.
   *
   * @author Chris Nokleberg
   * @author Ben Yu
   */
  public class AbstractIdleServiceTest extends TestCase {
   
  // Functional tests using real thread. We only verify publicly visible state.
   // Interaction assertions are done by the single-threaded unit tests.
   
  public static class FunctionalTest extends TestCase {
   
  private static class DefaultService extends AbstractIdleService {
   @Override protected void startUp() throws Exception {}
   @Override protected void shutDown() throws Exception {}
   }
   
  public void testServiceStartStop() throws Exception {
   AbstractIdleService service = new DefaultService();
   service.startAsync().awaitRunning();
   assertEquals(Service.State.RUNNING, service.state());
   service.stopAsync().awaitTerminated();
   assertEquals(Service.State.TERMINATED, service.state());
   }
   
  public void testStart_failed() throws Exception {
   final Exception exception = new Exception("deliberate");
   AbstractIdleService service = new DefaultService() {
   @Override protected void startUp() throws Exception {
   throw exception;
   }
   };
   try {
   service.startAsync().awaitRunning();
   fail();
   } catch (RuntimeException e) {
   assertSame(exception, e.getCause());
   }
   assertEquals(Service.State.FAILED, service.state());
   }
   
  public void testStop_failed() throws Exception {
   final Exception exception = new Exception("deliberate");
   AbstractIdleService service = new DefaultService() {
   @Override protected void shutDown() throws Exception {
   throw exception;
   }
   };
   service.startAsync().awaitRunning();
   try {
   service.stopAsync().awaitTerminated();
   fail();
   } catch (RuntimeException e) {
   assertSame(exception, e.getCause());
   }
   assertEquals(Service.State.FAILED, service.state());
   }
   }
   
  public void testStart() {
   TestService service = new TestService();
   assertEquals(0, service.startUpCalled);
   service.startAsync().awaitRunning();
   assertEquals(1, service.startUpCalled);
   assertEquals(Service.State.RUNNING, service.state());
   ASSERT.that(service.transitionStates).has().exactly(Service.State.STARTING).inOrder();
   }
   
  public void testStart_failed() {
   final Exception exception = new Exception("deliberate");
   TestService service = new TestService() {
   @Override protected void startUp() throws Exception {
   super.startUp();
   throw exception;
   }
   };
   assertEquals(0, service.startUpCalled);
   try {
   service.startAsync().awaitRunning();
   fail();
   } catch (RuntimeException e) {
   assertSame(exception, e.getCause());
   }
   assertEquals(1, service.startUpCalled);
   assertEquals(Service.State.FAILED, service.state());
   ASSERT.that(service.transitionStates).has().exactly(Service.State.STARTING).inOrder();
   }
   
  public void testStop_withoutStart() {
   TestService service = new TestService();
   service.stopAsync().awaitTerminated();
   assertEquals(0, service.startUpCalled);
   assertEquals(0, service.shutDownCalled);
   assertEquals(Service.State.TERMINATED, service.state());
   ASSERT.that(service.transitionStates).isEmpty();
   }
   
  public void testStop_afterStart() {
   TestService service = new TestService();
   service.startAsync().awaitRunning();
   assertEquals(1, service.startUpCalled);
   assertEquals(0, service.shutDownCalled);
   service.stopAsync().awaitTerminated();
   assertEquals(1, service.startUpCalled);
   assertEquals(1, service.shutDownCalled);
   assertEquals(Service.State.TERMINATED, service.state());
   ASSERT.that(service.transitionStates)
   .has().exactly(Service.State.STARTING, Service.State.STOPPING).inOrder();
   }
   
  public void testStop_failed() {
   final Exception exception = new Exception("deliberate");
   TestService service = new TestService() {
   @Override protected void shutDown() throws Exception {
   super.shutDown();
   throw exception;
   }
   };
   service.startAsync().awaitRunning();
   assertEquals(1, service.startUpCalled);
   assertEquals(0, service.shutDownCalled);
   try {
   service.stopAsync().awaitTerminated();
   fail();
   } catch (RuntimeException e) {
   assertSame(exception, e.getCause());
   }
   assertEquals(1, service.startUpCalled);
   assertEquals(1, service.shutDownCalled);
   assertEquals(Service.State.FAILED, service.state());
   ASSERT.that(service.transitionStates)
   .has().exactly(Service.State.STARTING, Service.State.STOPPING).inOrder();
   }
   
  public void testServiceToString() {
   AbstractIdleService service = new TestService();
   assertEquals("TestService [NEW]", service.toString());
   service.startAsync().awaitRunning();
   assertEquals("TestService [RUNNING]", service.toString());
   service.stopAsync().awaitTerminated();
   assertEquals("TestService [TERMINATED]", service.toString());
   }
   
  public void testTimeout() throws Exception {
   // Create a service whose executor will never run its commands
   Service service = new TestService() {
   @Override protected Executor executor() {
   return new Executor() {
   @Override public void execute(Runnable command) {}
   };
   }
   };
   try {
   service.startAsync().awaitRunning(1, TimeUnit.MILLISECONDS);
   fail("Expected timeout");
   } catch (TimeoutException e) {
   ASSERT.that(e.getMessage()).contains(Service.State.STARTING.toString());
   }
   }
   
  private static class TestService extends AbstractIdleService {
   int startUpCalled = 0;
   int shutDownCalled = 0;
   final List<State> transitionStates = Lists.newArrayList();
   
  @Override protected void startUp() throws Exception {
   assertEquals(0, startUpCalled);
   assertEquals(0, shutDownCalled);
   startUpCalled++;
   assertEquals(State.STARTING, state());
   }
   
  @Override protected void shutDown() throws Exception {
   assertEquals(1, startUpCalled);
   assertEquals(0, shutDownCalled);
   shutDownCalled++;
   assertEquals(State.STOPPING, state());
   }
   
  @Override protected Executor executor() {
   transitionStates.add(state());
   return MoreExecutors.sameThreadExecutor();
   }
   }
  }
   
  <pre>
AbstractScheduledServiceTest

  </pre>
  /*
   * Copyright (C) 2011 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.util.concurrent.AbstractScheduledService.Scheduler;
  import com.google.common.util.concurrent.Service.State;
   
  import junit.framework.TestCase;
   
  import java.util.concurrent.CountDownLatch;
  import java.util.concurrent.CyclicBarrier;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.Executors;
  import java.util.concurrent.Future;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.ScheduledFuture;
  import java.util.concurrent.ScheduledThreadPoolExecutor;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.concurrent.atomic.AtomicInteger;
   
  /**
   * Unit test for {@link AbstractScheduledService}.
   *
   * @author Luke Sandberg
   */
   
  public class AbstractScheduledServiceTest extends TestCase {
   
  volatile Scheduler configuration = Scheduler.newFixedDelaySchedule(0, 10, TimeUnit.MILLISECONDS);
   volatile ScheduledFuture<?> future = null;
   
  volatile boolean atFixedRateCalled = false;
   volatile boolean withFixedDelayCalled = false;
   volatile boolean scheduleCalled = false;
   
  final ScheduledExecutorService executor = new ScheduledThreadPoolExecutor(10) {
   @Override
   public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay,
   long delay, TimeUnit unit) {
   return future = super.scheduleWithFixedDelay(command, initialDelay, delay, unit);
   }
   };
   
  public void testServiceStartStop() throws Exception {
   NullService service = new NullService();
   service.startAsync().awaitRunning();
   assertFalse(future.isDone());
   service.stopAsync().awaitTerminated();
   assertTrue(future.isCancelled());
   }
   
  private class NullService extends AbstractScheduledService {
   @Override protected void runOneIteration() throws Exception {}
   @Override protected Scheduler scheduler() { return configuration; }
   @Override protected ScheduledExecutorService executor() { return executor; }
   }
   
  public void testFailOnExceptionFromRun() throws Exception {
   TestService service = new TestService();
   service.runException = new Exception();
   service.startAsync().awaitRunning();
   service.runFirstBarrier.await();
   service.runSecondBarrier.await();
   try {
   future.get();
   fail();
   } catch (ExecutionException e) {
   // An execution exception holds a runtime exception (from throwables.propogate) that holds our
   // original exception.
   assertEquals(service.runException, e.getCause().getCause());
   }
   assertEquals(service.state(), Service.State.FAILED);
   }
   
  public void testFailOnExceptionFromStartUp() {
   TestService service = new TestService();
   service.startUpException = new Exception();
   try {
   service.startAsync().awaitRunning();
   fail();
   } catch (IllegalStateException e) {
   assertEquals(service.startUpException, e.getCause());
   }
   assertEquals(0, service.numberOfTimesRunCalled.get());
   assertEquals(Service.State.FAILED, service.state());
   }
   
  public void testFailOnExceptionFromShutDown() throws Exception {
   TestService service = new TestService();
   service.shutDownException = new Exception();
   service.startAsync().awaitRunning();
   service.runFirstBarrier.await();
   service.stopAsync();
   service.runSecondBarrier.await();
   try {
   service.awaitTerminated();
   fail();
   } catch (IllegalStateException e) {
   assertEquals(service.shutDownException, e.getCause());
   }
   assertEquals(Service.State.FAILED, service.state());
   }
   
  public void testRunOneIterationCalledMultipleTimes() throws Exception {
   TestService service = new TestService();
   service.startAsync().awaitRunning();
   for (int i = 1; i < 10; i++) {
   service.runFirstBarrier.await();
   assertEquals(i, service.numberOfTimesRunCalled.get());
   service.runSecondBarrier.await();
   }
   service.runFirstBarrier.await();
   service.stopAsync();
   service.runSecondBarrier.await();
   service.stopAsync().awaitTerminated();
   }
   
  public void testExecutorOnlyCalledOnce() throws Exception {
   TestService service = new TestService();
   service.startAsync().awaitRunning();
   // It should be called once during startup.
   assertEquals(1, service.numberOfTimesExecutorCalled.get());
   for (int i = 1; i < 10; i++) {
   service.runFirstBarrier.await();
   assertEquals(i, service.numberOfTimesRunCalled.get());
   service.runSecondBarrier.await();
   }
   service.runFirstBarrier.await();
   service.stopAsync();
   service.runSecondBarrier.await();
   service.stopAsync().awaitTerminated();
   // Only called once overall.
   assertEquals(1, service.numberOfTimesExecutorCalled.get());
   }
   
  public void testDefaultExecutorIsShutdownWhenServiceIsStopped() throws Exception {
   final CountDownLatch terminationLatch = new CountDownLatch(1);
   AbstractScheduledService service = new AbstractScheduledService() {
   volatile ScheduledExecutorService executorService;
   @Override protected void runOneIteration() throws Exception {}
   
  @Override protected ScheduledExecutorService executor() {
   if (executorService == null) {
   executorService = super.executor();
   // Add a listener that will be executed after the listener that shuts down the executor.
   addListener(new Listener() {
   @Override public void terminated(State from) {
   terminationLatch.countDown();
   }
   }, MoreExecutors.sameThreadExecutor());
   }
   return executorService;
   }
   
  @Override protected Scheduler scheduler() {
   return Scheduler.newFixedDelaySchedule(0, 1, TimeUnit.MILLISECONDS);
   }};
   
  service.startAsync();
   assertFalse(service.executor().isShutdown());
   service.awaitRunning();
   service.stopAsync();
   terminationLatch.await();
   assertTrue(service.executor().isShutdown());
   assertTrue(service.executor().awaitTermination(100, TimeUnit.MILLISECONDS));
   }
   
  public void testDefaultExecutorIsShutdownWhenServiceFails() throws Exception {
   final CountDownLatch failureLatch = new CountDownLatch(1);
   AbstractScheduledService service = new AbstractScheduledService() {
   volatile ScheduledExecutorService executorService;
   @Override protected void runOneIteration() throws Exception {}
   
  @Override protected void startUp() throws Exception {
   throw new Exception("Failed");
   }
   
  @Override protected ScheduledExecutorService executor() {
   if (executorService == null) {
   executorService = super.executor();
   // Add a listener that will be executed after the listener that shuts down the executor.
   addListener(new Listener() {
   @Override public void failed(State from, Throwable failure) {
   failureLatch.countDown();
   }
   }, MoreExecutors.sameThreadExecutor());
   }
   return executorService;
   }
   
  @Override protected Scheduler scheduler() {
   return Scheduler.newFixedDelaySchedule(0, 1, TimeUnit.MILLISECONDS);
   }};
   
  try {
   service.startAsync().awaitRunning();
   fail("Expected service to fail during startup");
   } catch (IllegalStateException expected) {}
   failureLatch.await();
   assertTrue(service.executor().isShutdown());
   assertTrue(service.executor().awaitTermination(100, TimeUnit.MILLISECONDS));
   }
   
  public void testSchedulerOnlyCalledOnce() throws Exception {
   TestService service = new TestService();
   service.startAsync().awaitRunning();
   // It should be called once during startup.
   assertEquals(1, service.numberOfTimesSchedulerCalled.get());
   for (int i = 1; i < 10; i++) {
   service.runFirstBarrier.await();
   assertEquals(i, service.numberOfTimesRunCalled.get());
   service.runSecondBarrier.await();
   }
   service.runFirstBarrier.await();
   service.stopAsync();
   service.runSecondBarrier.await();
   service.awaitTerminated();
   // Only called once overall.
   assertEquals(1, service.numberOfTimesSchedulerCalled.get());
   }
   
  private class TestService extends AbstractScheduledService {
   CyclicBarrier runFirstBarrier = new CyclicBarrier(2);
   CyclicBarrier runSecondBarrier = new CyclicBarrier(2);
   
  volatile boolean startUpCalled = false;
   volatile boolean shutDownCalled = false;
   AtomicInteger numberOfTimesRunCalled = new AtomicInteger(0);
   AtomicInteger numberOfTimesExecutorCalled = new AtomicInteger(0);
   AtomicInteger numberOfTimesSchedulerCalled = new AtomicInteger(0);
   volatile Exception runException = null;
   volatile Exception startUpException = null;
   volatile Exception shutDownException = null;
   
  @Override
   protected void runOneIteration() throws Exception {
   assertTrue(startUpCalled);
   assertFalse(shutDownCalled);
   numberOfTimesRunCalled.incrementAndGet();
   assertEquals(State.RUNNING, state());
   runFirstBarrier.await();
   runSecondBarrier.await();
   if (runException != null) {
   throw runException;
   }
   }
   
  @Override
   protected void startUp() throws Exception {
   assertFalse(startUpCalled);
   assertFalse(shutDownCalled);
   startUpCalled = true;
   assertEquals(State.STARTING, state());
   if (startUpException != null) {
   throw startUpException;
   }
   }
   
  @Override
   protected void shutDown() throws Exception {
   assertTrue(startUpCalled);
   assertFalse(shutDownCalled);
   shutDownCalled = true;
   if (shutDownException != null) {
   throw shutDownException;
   }
   }
   
  @Override
   protected ScheduledExecutorService executor() {
   numberOfTimesExecutorCalled.incrementAndGet();
   return executor;
   }
   
  @Override
   protected Scheduler scheduler() {
   numberOfTimesSchedulerCalled.incrementAndGet();
   return configuration;
   }
   }
   
  public static class SchedulerTest extends TestCase {
   // These constants are arbitrary and just used to make sure that the correct method is called
   // with the correct parameters.
   private static final int initialDelay = 10;
   private static final int delay = 20;
   private static final TimeUnit unit = TimeUnit.MILLISECONDS;
   
  // Unique runnable object used for comparison.
   final Runnable testRunnable = new Runnable() {@Override public void run() {}};
   boolean called = false;
   
  private void assertSingleCallWithCorrectParameters(Runnable command, long initialDelay,
   long delay, TimeUnit unit) {
   assertFalse(called); // only called once.
   called = true;
   assertEquals(SchedulerTest.initialDelay, initialDelay);
   assertEquals(SchedulerTest.delay, delay);
   assertEquals(SchedulerTest.unit, unit);
   assertEquals(testRunnable, command);
   }
   
  public void testFixedRateSchedule() {
   Scheduler schedule = Scheduler.newFixedRateSchedule(initialDelay, delay, unit);
   schedule.schedule(null, new ScheduledThreadPoolExecutor(1) {
   @Override
   public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay,
   long period, TimeUnit unit) {
   assertSingleCallWithCorrectParameters(command, initialDelay, delay, unit);
   return null;
   }
   }, testRunnable);
   assertTrue(called);
   }
   
  public void testFixedDelaySchedule() {
   Scheduler schedule = Scheduler.newFixedDelaySchedule(initialDelay, delay, unit);
   schedule.schedule(null, new ScheduledThreadPoolExecutor(10) {
   @Override
   public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay,
   long delay, TimeUnit unit) {
   assertSingleCallWithCorrectParameters(command, initialDelay, delay, unit);
   return null;
   }
   }, testRunnable);
   assertTrue(called);
   }
   
  private class TestCustomScheduler extends AbstractScheduledService.CustomScheduler {
   public AtomicInteger scheduleCounter = new AtomicInteger(0);
   @Override
   protected Schedule getNextSchedule() throws Exception {
   scheduleCounter.incrementAndGet();
   return new Schedule(0, TimeUnit.SECONDS);
   }
   }
   
  public void testCustomSchedule_startStop() throws Exception {
   final CyclicBarrier firstBarrier = new CyclicBarrier(2);
   final CyclicBarrier secondBarrier = new CyclicBarrier(2);
   final AtomicBoolean shouldWait = new AtomicBoolean(true);
   Runnable task = new Runnable() {
   @Override public void run() {
   try {
   if (shouldWait.get()) {
   firstBarrier.await();
   secondBarrier.await();
   }
   } catch (Exception e) {
   throw new RuntimeException(e);
   }
   }
   };
   TestCustomScheduler scheduler = new TestCustomScheduler();
   Future<?> future = scheduler.schedule(null, Executors.newScheduledThreadPool(10), task);
   firstBarrier.await();
   assertEquals(1, scheduler.scheduleCounter.get());
   secondBarrier.await();
   firstBarrier.await();
   assertEquals(2, scheduler.scheduleCounter.get());
   shouldWait.set(false);
   secondBarrier.await();
   future.cancel(false);
   }
   
  public void testCustomSchedulerServiceStop() throws Exception {
   TestAbstractScheduledCustomService service = new TestAbstractScheduledCustomService();
   service.startAsync().awaitRunning();
   service.firstBarrier.await();
   assertEquals(1, service.numIterations.get());
   service.stopAsync();
   service.secondBarrier.await();
   service.awaitTerminated();
   // Sleep for a while just to ensure that our task wasn't called again.
   Thread.sleep(unit.toMillis(3 * delay));
   assertEquals(1, service.numIterations.get());
   }
   
  public void testBig() throws Exception {
   TestAbstractScheduledCustomService service = new TestAbstractScheduledCustomService() {
   @Override protected Scheduler scheduler() {
   return new AbstractScheduledService.CustomScheduler() {
   @Override
   protected Schedule getNextSchedule() throws Exception {
   // Explicitly yield to increase the probability of a pathological scheduling.
   Thread.yield();
   return new Schedule(0, TimeUnit.SECONDS);
   }
   };
   }
   };
   service.useBarriers = false;
   service.startAsync().awaitRunning();
   Thread.sleep(50);
   service.useBarriers = true;
   service.firstBarrier.await();
   int numIterations = service.numIterations.get();
   service.stopAsync();
   service.secondBarrier.await();
   service.awaitTerminated();
   assertEquals(numIterations, service.numIterations.get());
   }
   
  private static class TestAbstractScheduledCustomService extends AbstractScheduledService {
   final AtomicInteger numIterations = new AtomicInteger(0);
   volatile boolean useBarriers = true;
   final CyclicBarrier firstBarrier = new CyclicBarrier(2);
   final CyclicBarrier secondBarrier = new CyclicBarrier(2);
   
  @Override protected void runOneIteration() throws Exception {
   numIterations.incrementAndGet();
   if (useBarriers) {
   firstBarrier.await();
   secondBarrier.await();
   }
   }
   
  @Override protected ScheduledExecutorService executor() {
   // use a bunch of threads so that weird overlapping schedules are more likely to happen.
   return Executors.newScheduledThreadPool(10);
   }
   
  @Override protected void startUp() throws Exception {}
   
  @Override protected void shutDown() throws Exception {}
   
  @Override protected Scheduler scheduler() {
   return new CustomScheduler() {
   @Override
   protected Schedule getNextSchedule() throws Exception {
   return new Schedule(delay, unit);
   }};
   }
   }
   
  public void testCustomSchedulerFailure() throws Exception {
   TestFailingCustomScheduledService service = new TestFailingCustomScheduledService();
   service.startAsync().awaitRunning();
   for (int i = 1; i < 4; i++) {
   service.firstBarrier.await();
   assertEquals(i, service.numIterations.get());
   service.secondBarrier.await();
   }
   Thread.sleep(1000);
   try {
   service.stopAsync().awaitTerminated(100, TimeUnit.SECONDS);
   fail();
   } catch (IllegalStateException e) {
   assertEquals(State.FAILED, service.state());
   }
   }
   
  private static class TestFailingCustomScheduledService extends AbstractScheduledService {
   final AtomicInteger numIterations = new AtomicInteger(0);
   final CyclicBarrier firstBarrier = new CyclicBarrier(2);
   final CyclicBarrier secondBarrier = new CyclicBarrier(2);
   
  @Override protected void runOneIteration() throws Exception {
   numIterations.incrementAndGet();
   firstBarrier.await();
   secondBarrier.await();
   }
   
  @Override protected ScheduledExecutorService executor() {
   // use a bunch of threads so that weird overlapping schedules are more likely to happen.
   return Executors.newScheduledThreadPool(10);
   }
   
  @Override protected Scheduler scheduler() {
   return new CustomScheduler() {
   @Override
   protected Schedule getNextSchedule() throws Exception {
   if (numIterations.get() > 2) {
   throw new IllegalStateException("Failed");
   }
   return new Schedule(delay, unit);
   }};
   }
   }
   }
  }
  <pre>
AbstractServiceTest

  </pre>
  /*
   * Copyright (C) 2009 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 static java.lang.Thread.currentThread;
  import static java.util.concurrent.TimeUnit.SECONDS;
   
  import com.google.common.collect.ImmutableList;
  import com.google.common.collect.Iterables;
  import com.google.common.collect.Lists;
  import com.google.common.util.concurrent.Service.Listener;
  import com.google.common.util.concurrent.Service.State;
   
  import junit.framework.TestCase;
   
  import java.lang.Thread.UncaughtExceptionHandler;
  import java.util.List;
  import java.util.concurrent.CountDownLatch;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicInteger;
  import java.util.concurrent.atomic.AtomicReference;
   
  import javax.annotation.concurrent.GuardedBy;
   
  /**
   * Unit test for {@link AbstractService}.
   *
   * @author Jesse Wilson
   */
  public class AbstractServiceTest extends TestCase {
   
  private Thread executionThread;
   private Throwable thrownByExecutionThread;
   
  public void testNoOpServiceStartStop() throws Exception {
   NoOpService service = new NoOpService();
   RecordingListener listener = RecordingListener.record(service);
   
  assertEquals(State.NEW, service.state());
   assertFalse(service.isRunning());
   assertFalse(service.running);
   
  service.startAsync();
   assertEquals(State.RUNNING, service.state());
   assertTrue(service.isRunning());
   assertTrue(service.running);
   
  service.stopAsync();
   assertEquals(State.TERMINATED, service.state());
   assertFalse(service.isRunning());
   assertFalse(service.running);
   assertEquals(
   ImmutableList.of(
   State.STARTING,
   State.RUNNING,
   State.STOPPING,
   State.TERMINATED),
   listener.getStateHistory());
   }
   
  public void testNoOpServiceStartAndWaitStopAndWait() throws Exception {
   NoOpService service = new NoOpService();
   
  service.startAsync().awaitRunning();
   assertEquals(State.RUNNING, service.state());
   
  service.stopAsync().awaitTerminated();
   assertEquals(State.TERMINATED, service.state());
   }
   
  public void testNoOpServiceStartAsyncAndAwaitStopAsyncAndAwait() throws Exception {
   NoOpService service = new NoOpService();
   
  service.startAsync().awaitRunning();
   assertEquals(State.RUNNING, service.state());
   
  service.stopAsync().awaitTerminated();
   assertEquals(State.TERMINATED, service.state());
   }
   
  public void testNoOpServiceStopIdempotence() throws Exception {
   NoOpService service = new NoOpService();
   RecordingListener listener = RecordingListener.record(service);
   service.startAsync().awaitRunning();
   assertEquals(State.RUNNING, service.state());
   
  service.stopAsync();
   service.stopAsync();
   assertEquals(State.TERMINATED, service.state());
   assertEquals(
   ImmutableList.of(
   State.STARTING,
   State.RUNNING,
   State.STOPPING,
   State.TERMINATED),
   listener.getStateHistory());
   }
   
  public void testNoOpServiceStopIdempotenceAfterWait() throws Exception {
   NoOpService service = new NoOpService();
   
  service.startAsync().awaitRunning();
   
  service.stopAsync().awaitTerminated();
   service.stopAsync();
   assertEquals(State.TERMINATED, service.state());
   }
   
  public void testNoOpServiceStopIdempotenceDoubleWait() throws Exception {
   NoOpService service = new NoOpService();
   
  service.startAsync().awaitRunning();
   assertEquals(State.RUNNING, service.state());
   
  service.stopAsync().awaitTerminated();
   service.stopAsync().awaitTerminated();
   assertEquals(State.TERMINATED, service.state());
   }
   
  public void testNoOpServiceStartStopAndWaitUninterruptible()
   throws Exception {
   NoOpService service = new NoOpService();
   
  currentThread().interrupt();
   try {
   service.startAsync().awaitRunning();
   assertEquals(State.RUNNING, service.state());
   
  service.stopAsync().awaitTerminated();
   assertEquals(State.TERMINATED, service.state());
   
  assertTrue(currentThread().isInterrupted());
   } finally {
   Thread.interrupted(); // clear interrupt for future tests
   }
   }
   
  private static class NoOpService extends AbstractService {
   boolean running = false;
   
  @Override protected void doStart() {
   assertFalse(running);
   running = true;
   notifyStarted();
   }
   
  @Override protected void doStop() {
   assertTrue(running);
   running = false;
   notifyStopped();
   }
   }
   
  public void testManualServiceStartStop() throws Exception {
   ManualSwitchedService service = new ManualSwitchedService();
   RecordingListener listener = RecordingListener.record(service);
   
  service.startAsync();
   assertEquals(State.STARTING, service.state());
   assertFalse(service.isRunning());
   assertTrue(service.doStartCalled);
   
  service.notifyStarted(); // usually this would be invoked by another thread
   assertEquals(State.RUNNING, service.state());
   assertTrue(service.isRunning());
   
  service.stopAsync();
   assertEquals(State.STOPPING, service.state());
   assertFalse(service.isRunning());
   assertTrue(service.doStopCalled);
   
  service.notifyStopped(); // usually this would be invoked by another thread
   assertEquals(State.TERMINATED, service.state());
   assertFalse(service.isRunning());
   assertEquals(
   ImmutableList.of(
   State.STARTING,
   State.RUNNING,
   State.STOPPING,
   State.TERMINATED),
   listener.getStateHistory());
   
  }
   
  public void testManualServiceNotifyStoppedWhileRunning() throws Exception {
   ManualSwitchedService service = new ManualSwitchedService();
   RecordingListener listener = RecordingListener.record(service);
   
  service.startAsync();
   service.notifyStarted();
   service.notifyStopped();
   assertEquals(State.TERMINATED, service.state());
   assertFalse(service.isRunning());
   assertFalse(service.doStopCalled);
   
  assertEquals(
   ImmutableList.of(
   State.STARTING,
   State.RUNNING,
   State.TERMINATED),
   listener.getStateHistory());
   }
   
  public void testManualServiceStopWhileStarting() throws Exception {
   ManualSwitchedService service = new ManualSwitchedService();
   RecordingListener listener = RecordingListener.record(service);
   
  service.startAsync();
   assertEquals(State.STARTING, service.state());
   assertFalse(service.isRunning());
   assertTrue(service.doStartCalled);
   
  service.stopAsync();
   assertEquals(State.STOPPING, service.state());
   assertFalse(service.isRunning());
   assertFalse(service.doStopCalled);
   
  service.notifyStarted();
   assertEquals(State.STOPPING, service.state());
   assertFalse(service.isRunning());
   assertTrue(service.doStopCalled);
   
  service.notifyStopped();
   assertEquals(State.TERMINATED, service.state());
   assertFalse(service.isRunning());
   assertEquals(
   ImmutableList.of(
   State.STARTING,
   State.STOPPING,
   State.TERMINATED),
   listener.getStateHistory());
   }
   
  /**
   * This tests for a bug where if {@link Service#stopAsync()} was called while the service was
   * {@link State#STARTING} more than once, the {@link Listener#stopping(State)} callback would get
   * called multiple times.
   */
   public void testManualServiceStopMultipleTimesWhileStarting() throws Exception {
   ManualSwitchedService service = new ManualSwitchedService();
   final AtomicInteger stopppingCount = new AtomicInteger();
   service.addListener(new Listener() {
   @Override public void stopping(State from) {
   stopppingCount.incrementAndGet();
   }
   }, MoreExecutors.sameThreadExecutor());
   
  service.startAsync();
   service.stopAsync();
   assertEquals(1, stopppingCount.get());
   service.stopAsync();
   assertEquals(1, stopppingCount.get());
   }
   
  public void testManualServiceStopWhileNew() throws Exception {
   ManualSwitchedService service = new ManualSwitchedService();
   RecordingListener listener = RecordingListener.record(service);
   
  service.stopAsync();
   assertEquals(State.TERMINATED, service.state());
   assertFalse(service.isRunning());
   assertFalse(service.doStartCalled);
   assertFalse(service.doStopCalled);
   assertEquals(ImmutableList.of(State.TERMINATED), listener.getStateHistory());
   }
   
  public void testManualServiceFailWhileStarting() throws Exception {
   ManualSwitchedService service = new ManualSwitchedService();
   RecordingListener listener = RecordingListener.record(service);
   service.startAsync();
   service.notifyFailed(EXCEPTION);
   assertEquals(ImmutableList.of(State.STARTING, State.FAILED), listener.getStateHistory());
   }
   
  public void testManualServiceFailWhileRunning() throws Exception {
   ManualSwitchedService service = new ManualSwitchedService();
   RecordingListener listener = RecordingListener.record(service);
   service.startAsync();
   service.notifyStarted();
   service.notifyFailed(EXCEPTION);
   assertEquals(ImmutableList.of(State.STARTING, State.RUNNING, State.FAILED),
   listener.getStateHistory());
   }
   
  public void testManualServiceFailWhileStopping() throws Exception {
   ManualSwitchedService service = new ManualSwitchedService();
   RecordingListener listener = RecordingListener.record(service);
   service.startAsync();
   service.notifyStarted();
   service.stopAsync();
   service.notifyFailed(EXCEPTION);
   assertEquals(ImmutableList.of(State.STARTING, State.RUNNING, State.STOPPING, State.FAILED),
   listener.getStateHistory());
   }
   
  public void testManualServiceUnrequestedStop() {
   ManualSwitchedService service = new ManualSwitchedService();
   
  service.startAsync();
   
  service.notifyStarted();
   assertEquals(State.RUNNING, service.state());
   assertTrue(service.isRunning());
   assertFalse(service.doStopCalled);
   
  service.notifyStopped();
   assertEquals(State.TERMINATED, service.state());
   assertFalse(service.isRunning());
   assertFalse(service.doStopCalled);
   }
   
  /**
   * The user of this service should call {@link #notifyStarted} and {@link
   * #notifyStopped} after calling {@link #startAsync} and {@link #stopAsync}.
   */
   private static class ManualSwitchedService extends AbstractService {
   boolean doStartCalled = false;
   boolean doStopCalled = false;
   
  @Override protected void doStart() {
   assertFalse(doStartCalled);
   doStartCalled = true;
   }
   
  @Override protected void doStop() {
   assertFalse(doStopCalled);
   doStopCalled = true;
   }
   }
   
  public void testAwaitTerminated() throws Exception {
   final NoOpService service = new NoOpService();
   Thread waiter = new Thread() {
   @Override public void run() {
   service.awaitTerminated();
   }
   };
   waiter.start();
   service.startAsync().awaitRunning();
   assertEquals(State.RUNNING, service.state());
   service.stopAsync();
   waiter.join(100); // ensure that the await in the other thread is triggered
   assertFalse(waiter.isAlive());
   }
   
  public void testAwaitTerminated_FailedService() throws Exception {
   final ManualSwitchedService service = new ManualSwitchedService();
   final AtomicReference<Throwable> exception = Atomics.newReference();
   Thread waiter = new Thread() {
   @Override public void run() {
   try {
   service.awaitTerminated();
   fail("Expected an IllegalStateException");
   } catch (Throwable t) {
   exception.set(t);
   }
   }
   };
   waiter.start();
   service.startAsync();
   service.notifyStarted();
   assertEquals(State.RUNNING, service.state());
   service.notifyFailed(EXCEPTION);
   assertEquals(State.FAILED, service.state());
   waiter.join(100);
   assertFalse(waiter.isAlive());
   assertTrue(exception.get() instanceof IllegalStateException);
   assertEquals(EXCEPTION, exception.get().getCause());
   }
   
  public void testThreadedServiceStartAndWaitStopAndWait() throws Throwable {
   ThreadedService service = new ThreadedService();
   RecordingListener listener = RecordingListener.record(service);
   service.startAsync().awaitRunning();
   assertEquals(State.RUNNING, service.state());
   
  service.awaitRunChecks();
   
  service.stopAsync().awaitTerminated();
   assertEquals(State.TERMINATED, service.state());
   
  throwIfSet(thrownByExecutionThread);
   assertEquals(
   ImmutableList.of(
   State.STARTING,
   State.RUNNING,
   State.STOPPING,
   State.TERMINATED),
   listener.getStateHistory());
   }
   
  public void testThreadedServiceStopIdempotence() throws Throwable {
   ThreadedService service = new ThreadedService();
   
  service.startAsync().awaitRunning();
   assertEquals(State.RUNNING, service.state());
   
  service.awaitRunChecks();
   
  service.stopAsync();
   service.stopAsync().awaitTerminated();
   assertEquals(State.TERMINATED, service.state());
   
  throwIfSet(thrownByExecutionThread);
   }
   
  public void testThreadedServiceStopIdempotenceAfterWait()
   throws Throwable {
   ThreadedService service = new ThreadedService();
   
  service.startAsync().awaitRunning();
   assertEquals(State.RUNNING, service.state());
   
  service.awaitRunChecks();
   
  service.stopAsync().awaitTerminated();
   service.stopAsync();
   assertEquals(State.TERMINATED, service.state());
   
  executionThread.join();
   
  throwIfSet(thrownByExecutionThread);
   }
   
  public void testThreadedServiceStopIdempotenceDoubleWait()
   throws Throwable {
   ThreadedService service = new ThreadedService();
   
  service.startAsync().awaitRunning();
   assertEquals(State.RUNNING, service.state());
   
  service.awaitRunChecks();
   
  service.stopAsync().awaitTerminated();
   service.stopAsync().awaitTerminated();
   assertEquals(State.TERMINATED, service.state());
   
  throwIfSet(thrownByExecutionThread);
   }
   
  public void testManualServiceFailureIdempotence() {
   ManualSwitchedService service = new ManualSwitchedService();
   RecordingListener.record(service);
   service.startAsync();
   service.notifyFailed(new Exception("1"));
   service.notifyFailed(new Exception("2"));
   assertEquals("1", service.failureCause().getMessage());
   try {
   service.awaitRunning();
   fail();
   } catch (IllegalStateException e) {
   assertEquals("1", e.getCause().getMessage());
   }
   }
   
  private class ThreadedService extends AbstractService {
   final CountDownLatch hasConfirmedIsRunning = new CountDownLatch(1);
   
  /*
   * The main test thread tries to stop() the service shortly after
   * confirming that it is running. Meanwhile, the service itself is trying
   * to confirm that it is running. If the main thread's stop() call happens
   * before it has the chance, the test will fail. To avoid this, the main
   * thread calls this method, which waits until the service has performed
   * its own "running" check.
   */
   void awaitRunChecks() throws InterruptedException {
   assertTrue("Service thread hasn't finished its checks. "
   + "Exception status (possibly stale): " + thrownByExecutionThread,
   hasConfirmedIsRunning.await(10, SECONDS));
   }
   
  @Override protected void doStart() {
   assertEquals(State.STARTING, state());
   invokeOnExecutionThreadForTest(new Runnable() {
   @Override public void run() {
   assertEquals(State.STARTING, state());
   notifyStarted();
   assertEquals(State.RUNNING, state());
   hasConfirmedIsRunning.countDown();
   }
   });
   }
   
  @Override protected void doStop() {
   assertEquals(State.STOPPING, state());
   invokeOnExecutionThreadForTest(new Runnable() {
   @Override public void run() {
   assertEquals(State.STOPPING, state());
   notifyStopped();
   assertEquals(State.TERMINATED, state());
   }
   });
   }
   }
   
  private void invokeOnExecutionThreadForTest(Runnable runnable) {
   executionThread = new Thread(runnable);
   executionThread.setUncaughtExceptionHandler(new UncaughtExceptionHandler() {
   @Override
   public void uncaughtException(Thread thread, Throwable e) {
   thrownByExecutionThread = e;
   }
   });
   executionThread.start();
   }
   
  private static void throwIfSet(Throwable t) throws Throwable {
   if (t != null) {
   throw t;
   }
   }
   
  public void testStopUnstartedService() throws Exception {
   NoOpService service = new NoOpService();
   RecordingListener listener = RecordingListener.record(service);
   
  service.stopAsync();
   assertEquals(State.TERMINATED, service.state());
   
  try {
   service.startAsync();
   fail();
   } catch (IllegalStateException expected) {}
   assertEquals(State.TERMINATED, Iterables.getOnlyElement(listener.getStateHistory()));
   }
   
  public void testFailingServiceStartAndWait() throws Exception {
   StartFailingService service = new StartFailingService();
   RecordingListener listener = RecordingListener.record(service);
   
  try {
   service.startAsync().awaitRunning();
   fail();
   } catch (IllegalStateException e) {
   assertEquals(EXCEPTION, service.failureCause());
   assertEquals(EXCEPTION, e.getCause());
   }
   assertEquals(
   ImmutableList.of(
   State.STARTING,
   State.FAILED),
   listener.getStateHistory());
   }
   
  public void testFailingServiceStopAndWait_stopFailing() throws Exception {
   StopFailingService service = new StopFailingService();
   RecordingListener listener = RecordingListener.record(service);
   
  service.startAsync().awaitRunning();
   try {
   service.stopAsync().awaitTerminated();
   fail();
   } catch (IllegalStateException e) {
   assertEquals(EXCEPTION, service.failureCause());
   assertEquals(EXCEPTION, e.getCause());
   }
   assertEquals(
   ImmutableList.of(
   State.STARTING,
   State.RUNNING,
   State.STOPPING,
   State.FAILED),
   listener.getStateHistory());
   }
   
  public void testFailingServiceStopAndWait_runFailing() throws Exception {
   RunFailingService service = new RunFailingService();
   RecordingListener listener = RecordingListener.record(service);
   
  service.startAsync();
   try {
   service.awaitRunning();
   fail();
   } catch (IllegalStateException e) {
   assertEquals(EXCEPTION, service.failureCause());
   assertEquals(EXCEPTION, e.getCause());
   }
   assertEquals(
   ImmutableList.of(
   State.STARTING,
   State.RUNNING,
   State.FAILED),
   listener.getStateHistory());
   }
   
  public void testThrowingServiceStartAndWait() throws Exception {
   StartThrowingService service = new StartThrowingService();
   RecordingListener listener = RecordingListener.record(service);
   
  try {
   service.startAsync().awaitRunning();
   fail();
   } catch (IllegalStateException e) {
   assertEquals(service.exception, service.failureCause());
   assertEquals(service.exception, e.getCause());
   }
   assertEquals(
   ImmutableList.of(
   State.STARTING,
   State.FAILED),
   listener.getStateHistory());
   }
   
  public void testThrowingServiceStopAndWait_stopThrowing() throws Exception {
   StopThrowingService service = new StopThrowingService();
   RecordingListener listener = RecordingListener.record(service);
   
  service.startAsync().awaitRunning();
   try {
   service.stopAsync().awaitTerminated();
   fail();
   } catch (IllegalStateException e) {
   assertEquals(service.exception, service.failureCause());
   assertEquals(service.exception, e.getCause());
   }
   assertEquals(
   ImmutableList.of(
   State.STARTING,
   State.RUNNING,
   State.STOPPING,
   State.FAILED),
   listener.getStateHistory());
   }
   
  public void testThrowingServiceStopAndWait_runThrowing() throws Exception {
   RunThrowingService service = new RunThrowingService();
   RecordingListener listener = RecordingListener.record(service);
   
  service.startAsync();
   try {
   service.awaitTerminated();
   fail();
   } catch (IllegalStateException e) {
   assertEquals(service.exception, service.failureCause());
   assertEquals(service.exception, e.getCause());
   }
   assertEquals(
   ImmutableList.of(
   State.STARTING,
   State.RUNNING,
   State.FAILED),
   listener.getStateHistory());
   }
   
  public void testFailureCause_throwsIfNotFailed() {
   StopFailingService service = new StopFailingService();
   try {
   service.failureCause();
   fail();
   } catch (IllegalStateException e) {
   // expected
   }
   service.startAsync().awaitRunning();
   try {
   service.failureCause();
   fail();
   } catch (IllegalStateException e) {
   // expected
   }
   try {
   service.stopAsync().awaitTerminated();
   fail();
   } catch (IllegalStateException e) {
   assertEquals(EXCEPTION, service.failureCause());
   assertEquals(EXCEPTION, e.getCause());
   }
   }
   
  public void testAddListenerAfterFailureDoesntCauseDeadlock() throws InterruptedException {
   final StartFailingService service = new StartFailingService();
   service.startAsync();
   assertEquals(State.FAILED, service.state());
   service.addListener(new RecordingListener(service), MoreExecutors.sameThreadExecutor());
   Thread thread = new Thread() {
   @Override public void run() {
   // Internally stopAsync() grabs a lock, this could be any such method on AbstractService.
   service.stopAsync();
   }
   };
   thread.start();
   thread.join(100);
   assertFalse(thread + " is deadlocked", thread.isAlive());
   }
   
  public void testListenerDoesntDeadlockOnStartAndWaitFromRunning() throws Exception {
   final NoOpThreadedService service = new NoOpThreadedService();
   service.addListener(new Listener() {
   @Override public void running() {
   service.awaitRunning();
   }
   }, MoreExecutors.sameThreadExecutor());
   service.startAsync().awaitRunning(10, TimeUnit.MILLISECONDS);
   service.stopAsync();
   }
   
  public void testListenerDoesntDeadlockOnStopAndWaitFromTerminated() throws Exception {
   final NoOpThreadedService service = new NoOpThreadedService();
   service.addListener(new Listener() {
   @Override public void terminated(State from) {
   service.stopAsync().awaitTerminated();
   }
   }, MoreExecutors.sameThreadExecutor());
   service.startAsync().awaitRunning();
   
  Thread thread = new Thread() {
   @Override public void run() {
   service.stopAsync().awaitTerminated();
   }
   };
   thread.start();
   thread.join(100);
   assertFalse(thread + " is deadlocked", thread.isAlive());
   }
   
  private static class NoOpThreadedService extends AbstractExecutionThreadService {
   final CountDownLatch latch = new CountDownLatch(1);
   @Override protected void run() throws Exception {
   latch.await();
   }
   @Override protected void triggerShutdown() {
   latch.countDown();
   }
   }
   
  private static class StartFailingService extends AbstractService {
   @Override protected void doStart() {
   notifyFailed(EXCEPTION);
   }
   
  @Override protected void doStop() {
   fail();
   }
   }
   
  private static class RunFailingService extends AbstractService {
   @Override protected void doStart() {
   notifyStarted();
   notifyFailed(EXCEPTION);
   }
   
  @Override protected void doStop() {
   fail();
   }
   }
   
  private static class StopFailingService extends AbstractService {
   @Override protected void doStart() {
   notifyStarted();
   }
   
  @Override protected void doStop() {
   notifyFailed(EXCEPTION);
   }
   }
   
  private static class StartThrowingService extends AbstractService {
   
  final RuntimeException exception = new RuntimeException("deliberate");
   
  @Override protected void doStart() {
   throw exception;
   }
   
  @Override protected void doStop() {
   fail();
   }
   }
   
  private static class RunThrowingService extends AbstractService {
   
  final RuntimeException exception = new RuntimeException("deliberate");
   
  @Override protected void doStart() {
   notifyStarted();
   throw exception;
   }
   
  @Override protected void doStop() {
   fail();
   }
   }
   
  private static class StopThrowingService extends AbstractService {
   
  final RuntimeException exception = new RuntimeException("deliberate");
   
  @Override protected void doStart() {
   notifyStarted();
   }
   
  @Override protected void doStop() {
   throw exception;
   }
   }
   
  private static class RecordingListener extends Listener {
   static RecordingListener record(Service service) {
   RecordingListener listener = new RecordingListener(service);
   service.addListener(listener, MoreExecutors.sameThreadExecutor());
   return listener;
   }
   
  final Service service;
   
  RecordingListener(Service service) {
   this.service = service;
   }
   
  @GuardedBy("this")
   final List<State> stateHistory = Lists.newArrayList();
   final CountDownLatch completionLatch = new CountDownLatch(1);
   
  ImmutableList<State> getStateHistory() throws Exception {
   completionLatch.await();
   synchronized (this) {
   return ImmutableList.copyOf(stateHistory);
   }
   }
   
  @Override public synchronized void starting() {
   assertTrue(stateHistory.isEmpty());
   assertNotSame(State.NEW, service.state());
   stateHistory.add(State.STARTING);
   }
   
  @Override public synchronized void running() {
   assertEquals(State.STARTING, Iterables.getOnlyElement(stateHistory));
   stateHistory.add(State.RUNNING);
   service.awaitRunning();
   assertNotSame(State.STARTING, service.state());
   }
   
  @Override public synchronized void stopping(State from) {
   assertEquals(from, Iterables.getLast(stateHistory));
   stateHistory.add(State.STOPPING);
   if (from == State.STARTING) {
   try {
   service.awaitRunning();
   fail();
   } catch (IllegalStateException expected) {
   assertNull(expected.getCause());
   assertTrue(expected.getMessage().equals(
   "Expected the service to be RUNNING, but was STOPPING"));
   }
   }
   assertNotSame(from, service.state());
   }
   
  @Override public synchronized void terminated(State from) {
   assertEquals(from, Iterables.getLast(stateHistory, State.NEW));
   stateHistory.add(State.TERMINATED);
   assertEquals(State.TERMINATED, service.state());
   if (from == State.NEW) {
   try {
   service.awaitRunning();
   fail();
   } catch (IllegalStateException expected) {
   assertNull(expected.getCause());
   assertTrue(expected.getMessage().equals(
   "Expected the service to be RUNNING, but was TERMINATED"));
   }
   }
   completionLatch.countDown();
   }
   
  @Override public synchronized void failed(State from, Throwable failure) {
   assertEquals(from, Iterables.getLast(stateHistory));
   stateHistory.add(State.FAILED);
   assertEquals(State.FAILED, service.state());
   assertEquals(failure, service.failureCause());
   if (from == State.STARTING) {
   try {
   service.awaitRunning();
   fail();
   } catch (IllegalStateException e) {
   assertEquals(failure, e.getCause());
   }
   }
   try {
   service.awaitTerminated();
   fail();
   } catch (IllegalStateException e) {
   assertEquals(failure, e.getCause());
   }
   completionLatch.countDown();
   }
   }
   
  public void testNotifyStartedWhenNotStarting() {
   AbstractService service = new DefaultService();
   try {
   service.notifyStarted();
   fail();
   } catch (IllegalStateException expected) {}
   }
   
  public void testNotifyStoppedWhenNotRunning() {
   AbstractService service = new DefaultService();
   try {
   service.notifyStopped();
   fail();
   } catch (IllegalStateException expected) {}
   }
   
  public void testNotifyFailedWhenNotStarted() {
   AbstractService service = new DefaultService();
   try {
   service.notifyFailed(new Exception());
   fail();
   } catch (IllegalStateException expected) {}
   }
   
  public void testNotifyFailedWhenTerminated() {
   NoOpService service = new NoOpService();
   service.startAsync().awaitRunning();
   service.stopAsync().awaitTerminated();
   try {
   service.notifyFailed(new Exception());
   fail();
   } catch (IllegalStateException expected) {}
   }
   
  private static class DefaultService extends AbstractService {
   @Override protected void doStart() {}
   @Override protected void doStop() {}
   }
   
  private static final Exception EXCEPTION = new Exception();
  }
  <pre>
ServiceManagerTest

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  </pre>
  /*
   * Copyright (C) 2012 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 static java.util.Arrays.asList;
   
  import com.google.common.collect.ImmutableMap;
  import com.google.common.collect.ImmutableSet;
  import com.google.common.collect.Lists;
  import com.google.common.collect.Sets;
  import com.google.common.testing.NullPointerTester;
  import com.google.common.testing.TestLogHandler;
  import com.google.common.util.concurrent.ServiceManager.Listener;
   
  import junit.framework.TestCase;
   
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.List;
  import java.util.Set;
  import java.util.concurrent.CountDownLatch;
  import java.util.concurrent.Executor;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  import java.util.logging.Formatter;
  import java.util.logging.Level;
  import java.util.logging.LogRecord;
  import java.util.logging.Logger;
   
  /**
   * Tests for {@link ServiceManager}.
   *
   * @author Luke Sandberg
   * @author Chris Nokleberg
   */
  public class ServiceManagerTest extends TestCase {
   
  private static class NoOpService extends AbstractService {
   @Override protected void doStart() {
   notifyStarted();
   }
   
  @Override protected void doStop() {
   notifyStopped();
   }
   }
   
  /*
   * A NoOp service that will delay the startup and shutdown notification for a configurable amount
   * of time.
   */
   private static class NoOpDelayedSerivce extends NoOpService {
   private long delay;
   
  public NoOpDelayedSerivce(long delay) {
   this.delay = delay;
   }
   
  @Override protected void doStart() {
   new Thread() {
   @Override public void run() {
   Uninterruptibles.sleepUninterruptibly(delay, TimeUnit.MILLISECONDS);
   notifyStarted();
   }
   }.start();
   }
   
  @Override protected void doStop() {
   new Thread() {
   @Override public void run() {
   Uninterruptibles.sleepUninterruptibly(delay, TimeUnit.MILLISECONDS);
   notifyStopped();
   }
   }.start();
   }
   }
   
  private static class FailStartService extends NoOpService {
   @Override protected void doStart() {
   notifyFailed(new IllegalStateException("failed"));
   }
   }
   
  private static class FailRunService extends NoOpService {
   @Override protected void doStart() {
   super.doStart();
   notifyFailed(new IllegalStateException("failed"));
   }
   }
   
  private static class FailStopService extends NoOpService {
   @Override protected void doStop() {
   notifyFailed(new IllegalStateException("failed"));
   }
   }
   
  public void testServiceStartupTimes() {
   Service a = new NoOpDelayedSerivce(150);
   Service b = new NoOpDelayedSerivce(353);
   ServiceManager serviceManager = new ServiceManager(asList(a, b));
   serviceManager.startAsync().awaitHealthy();
   ImmutableMap<Service, Long> startupTimes = serviceManager.startupTimes();
   assertEquals(2, startupTimes.size());
   assertTrue(startupTimes.get(a) >= 150);
   assertTrue(startupTimes.get(b) >= 353);
   }
   
  public void testServiceStartStop() {
   Service a = new NoOpService();
   Service b = new NoOpService();
   ServiceManager manager = new ServiceManager(asList(a, b));
   RecordingListener listener = new RecordingListener();
   manager.addListener(listener);
   assertState(manager, Service.State.NEW, a, b);
   assertFalse(manager.isHealthy());
   manager.startAsync().awaitHealthy();
   assertState(manager, Service.State.RUNNING, a, b);
   assertTrue(manager.isHealthy());
   assertTrue(listener.healthyCalled);
   assertFalse(listener.stoppedCalled);
   assertTrue(listener.failedServices.isEmpty());
   manager.stopAsync().awaitStopped();
   assertState(manager, Service.State.TERMINATED, a, b);
   assertFalse(manager.isHealthy());
   assertTrue(listener.stoppedCalled);
   assertTrue(listener.failedServices.isEmpty());
   }
   
  public void testFailStart() throws Exception {
   Service a = new NoOpService();
   Service b = new FailStartService();
   Service c = new NoOpService();
   Service d = new FailStartService();
   Service e = new NoOpService();
   ServiceManager manager = new ServiceManager(asList(a, b, c, d, e));
   RecordingListener listener = new RecordingListener();
   manager.addListener(listener);
   assertState(manager, Service.State.NEW, a, b, c, d, e);
   try {
   manager.startAsync().awaitHealthy();
   fail();
   } catch (IllegalStateException expected) {
   }
   assertFalse(listener.healthyCalled);
   assertState(manager, Service.State.RUNNING, a, c, e);
   assertEquals(ImmutableSet.of(b, d), listener.failedServices);
   assertState(manager, Service.State.FAILED, b, d);
   assertFalse(manager.isHealthy());
   
  manager.stopAsync().awaitStopped();
   assertFalse(manager.isHealthy());
   assertFalse(listener.healthyCalled);
   assertTrue(listener.stoppedCalled);
   }
   
  public void testFailRun() throws Exception {
   Service a = new NoOpService();
   Service b = new FailRunService();
   ServiceManager manager = new ServiceManager(asList(a, b));
   RecordingListener listener = new RecordingListener();
   manager.addListener(listener);
   assertState(manager, Service.State.NEW, a, b);
   try {
   manager.startAsync().awaitHealthy();
   fail();
   } catch (IllegalStateException expected) {
   }
   assertTrue(listener.healthyCalled);
   assertEquals(ImmutableSet.of(b), listener.failedServices);
   
  manager.stopAsync().awaitStopped();
   assertState(manager, Service.State.FAILED, b);
   assertState(manager, Service.State.TERMINATED, a);
   
  assertTrue(listener.stoppedCalled);
   }
   
  public void testFailStop() throws Exception {
   Service a = new NoOpService();
   Service b = new FailStopService();
   Service c = new NoOpService();
   ServiceManager manager = new ServiceManager(asList(a, b, c));
   RecordingListener listener = new RecordingListener();
   manager.addListener(listener);
   
  manager.startAsync().awaitHealthy();
   assertTrue(listener.healthyCalled);
   assertFalse(listener.stoppedCalled);
   manager.stopAsync().awaitStopped();
   
  assertTrue(listener.stoppedCalled);
   assertEquals(ImmutableSet.of(b), listener.failedServices);
   assertState(manager, Service.State.FAILED, b);
   assertState(manager, Service.State.TERMINATED, a, c);
   }
   
  public void testToString() throws Exception {
   Service a = new NoOpService();
   Service b = new FailStartService();
   ServiceManager manager = new ServiceManager(asList(a, b));
   String toString = manager.toString();
   assertTrue(toString.contains("NoOpService"));
   assertTrue(toString.contains("FailStartService"));
   }
   
  public void testTimeouts() throws Exception {
   Service a = new NoOpDelayedSerivce(50);
   ServiceManager manager = new ServiceManager(asList(a));
   manager.startAsync();
   try {
   manager.awaitHealthy(1, TimeUnit.MILLISECONDS);
   fail();
   } catch (TimeoutException expected) {
   }
   manager.awaitHealthy(100, TimeUnit.MILLISECONDS); // no exception thrown
   
  manager.stopAsync();
   try {
   manager.awaitStopped(1, TimeUnit.MILLISECONDS);
   fail();
   } catch (TimeoutException expected) {
   }
   manager.awaitStopped(100, TimeUnit.MILLISECONDS); // no exception thrown
   }
   
  /**
   * This covers a case where if the last service to stop failed then the stopped callback would
   * never be called.
   */
   public void testSingleFailedServiceCallsStopped() {
   Service a = new FailStartService();
   ServiceManager manager = new ServiceManager(asList(a));
   RecordingListener listener = new RecordingListener();
   manager.addListener(listener);
   try {
   manager.startAsync().awaitHealthy();
   fail();
   } catch (IllegalStateException expected) {
   }
   assertTrue(listener.stoppedCalled);
   }
   
  /**
   * This covers a bug where listener.healthy would get called when a single service failed during
   * startup (it occurred in more complicated cases also).
   */
   public void testFailStart_singleServiceCallsHealthy() {
   Service a = new FailStartService();
   ServiceManager manager = new ServiceManager(asList(a));
   RecordingListener listener = new RecordingListener();
   manager.addListener(listener);
   try {
   manager.startAsync().awaitHealthy();
   fail();
   } catch (IllegalStateException expected) {
   }
   assertFalse(listener.healthyCalled);
   }
   
  /**
   * This covers a bug where if a listener was installed that would stop the manager if any service
   * fails and something failed during startup before service.start was called on all the services,
   * then awaitStopped would deadlock due to an IllegalStateException that was thrown when trying to
   * stop the timer(!).
   */
   public void testFailStart_stopOthers() throws TimeoutException {
   Service a = new FailStartService();
   Service b = new NoOpService();
   final ServiceManager manager = new ServiceManager(asList(a, b));
   manager.addListener(new Listener() {
   @Override public void failure(Service service) {
   manager.stopAsync();
   }});
   manager.startAsync();
   manager.awaitStopped(10, TimeUnit.MILLISECONDS);
   }
   
  private static void assertState(
   ServiceManager manager, Service.State state, Service... services) {
   Collection<Service> managerServices = manager.servicesByState().get(state);
   for (Service service : services) {
   assertEquals(service.toString(), state, service.state());
   assertEquals(service.toString(), service.isRunning(), state == Service.State.RUNNING);
   assertTrue(managerServices + " should contain " + service, managerServices.contains(service));
   }
   }
   
  /**
   * This is for covering a case where the ServiceManager would behave strangely if constructed
   * with no service under management. Listeners would never fire because the ServiceManager was
   * healthy and stopped at the same time. This test ensures that listeners fire and isHealthy
   * makes sense.
   */
   public void testEmptyServiceManager() {
   Logger logger = Logger.getLogger(ServiceManager.class.getName());
   logger.setLevel(Level.FINEST);
   TestLogHandler logHandler = new TestLogHandler();
   logger.addHandler(logHandler);
   ServiceManager manager = new ServiceManager(Arrays.<Service>asList());
   RecordingListener listener = new RecordingListener();
   manager.addListener(listener, MoreExecutors.sameThreadExecutor());
   manager.startAsync().awaitHealthy();
   assertTrue(manager.isHealthy());
   assertTrue(listener.healthyCalled);
   assertFalse(listener.stoppedCalled);
   assertTrue(listener.failedServices.isEmpty());
   manager.stopAsync().awaitStopped();
   assertFalse(manager.isHealthy());
   assertTrue(listener.stoppedCalled);
   assertTrue(listener.failedServices.isEmpty());
   // check that our NoOpService is not directly observable via any of the inspection methods or
   // via logging.
   assertEquals("ServiceManager{services=[]}", manager.toString());
   assertTrue(manager.servicesByState().isEmpty());
   assertTrue(manager.startupTimes().isEmpty());
   Formatter logFormatter = new Formatter() {
   @Override public String format(LogRecord record) {
   return formatMessage(record);
   }
   };
   for (LogRecord record : logHandler.getStoredLogRecords()) {
   assertFalse(logFormatter.format(record).contains("NoOpService"));
   }
   }
   
  /**
   * This is for a case where a long running Listener using the sameThreadListener could deadlock
   * another thread calling stopAsync().
   */
   
  public void testListenerDeadlock() throws InterruptedException {
   final CountDownLatch failEnter = new CountDownLatch(1);
   Service failRunService = new AbstractService() {
   @Override protected void doStart() {
   new Thread() {
   @Override public void run() {
   notifyStarted();
   notifyFailed(new Exception("boom"));
   }
   }.start();
   }
   @Override protected void doStop() {
   notifyStopped();
   }
   };
   final ServiceManager manager = new ServiceManager(
   Arrays.asList(failRunService, new NoOpService()));
   manager.addListener(new ServiceManager.Listener() {
   @Override public void failure(Service service) {
   failEnter.countDown();
   // block forever!
   Uninterruptibles.awaitUninterruptibly(new CountDownLatch(1));
   }
   }, MoreExecutors.sameThreadExecutor());
   // We do not call awaitHealthy because, due to races, that method may throw an exception. But
   // we really just want to wait for the thread to be in the failure callback so we wait for that
   // explicitly instead.
   manager.startAsync();
   failEnter.await();
   assertFalse("State should be updated before calling listeners", manager.isHealthy());
   // now we want to stop the services.
   Thread stoppingThread = new Thread() {
   @Override public void run() {
   manager.stopAsync().awaitStopped();
   }
   };
   stoppingThread.start();
   // this should be super fast since the only non stopped service is a NoOpService
   stoppingThread.join(1000);
   assertFalse("stopAsync has deadlocked!.", stoppingThread.isAlive());
   }
   
  /**
   * Catches a bug where when constructing a service manager failed, later interactions with the
   * service could cause IllegalStateExceptions inside the partially constructed ServiceManager.
   * This ISE wouldn't actually bubble up but would get logged by ExecutionQueue. This obfuscated
   * the original error (which was not constructing ServiceManager correctly).
   */
   public void testPartiallyConstructedManager() {
   Logger logger = Logger.getLogger("global");
   logger.setLevel(Level.FINEST);
   TestLogHandler logHandler = new TestLogHandler();
   logger.addHandler(logHandler);
   NoOpService service = new NoOpService();
   service.startAsync();
   try {
   new ServiceManager(Arrays.asList(service));
   fail();
   } catch (IllegalArgumentException expected) {}
   service.stopAsync();
   // Nothing was logged!
   assertEquals(0, logHandler.getStoredLogRecords().size());
   }
   
  public void testPartiallyConstructedManager_transitionAfterAddListenerBeforeStateIsReady() {
   // The implementation of this test is pretty sensitive to the implementation :( but we want to
   // ensure that if weird things happen during construction then we get exceptions.
   final NoOpService service1 = new NoOpService();
   // This service will start service1 when addListener is called. This simulates service1 being
   // started asynchronously.
   Service service2 = new Service() {
   final NoOpService delegate = new NoOpService();
   @Override public final void addListener(Listener listener, Executor executor) {
   service1.startAsync();
   delegate.addListener(listener, executor);
   }
   // Delegates from here on down
   @Override public final Service startAsync() {
   return delegate.startAsync();
   }
   
  @Override public final Service stopAsync() {
   return delegate.stopAsync();
   }
   
  @Override public final ListenableFuture<State> start() {
   return delegate.start();
   }
   
  @Override public final ListenableFuture<State> stop() {
   return delegate.stop();
   }
   
  @Override public State startAndWait() {
   return delegate.startAndWait();
   }
   
  @Override public State stopAndWait() {
   return delegate.stopAndWait();
   }
   
  @Override public final void awaitRunning() {
   delegate.awaitRunning();
   }
   
  @Override public final void awaitRunning(long timeout, TimeUnit unit)
   throws TimeoutException {
   delegate.awaitRunning(timeout, unit);
   }
   
  @Override public final void awaitTerminated() {
   delegate.awaitTerminated();
   }
   
  @Override public final void awaitTerminated(long timeout, TimeUnit unit)
   throws TimeoutException {
   delegate.awaitTerminated(timeout, unit);
   }
   
  @Override public final boolean isRunning() {
   return delegate.isRunning();
   }
   
  @Override public final State state() {
   return delegate.state();
   }
   
  @Override public final Throwable failureCause() {
   return delegate.failureCause();
   }
   };
   try {
   new ServiceManager(Arrays.asList(service1, service2));
   fail();
   } catch (IllegalArgumentException expected) {
   assertTrue(expected.getMessage().contains("started transitioning asynchronously"));
   }
   }
   
  /**
   * This test is for a case where two Service.Listener callbacks for the same service would call
   * transitionService in the wrong order due to a race. Due to the fact that it is a race this
   * test isn't guaranteed to expose the issue, but it is at least likely to become flaky if the
   * race sneaks back in, and in this case flaky means something is definitely wrong.
   *
   * <p>Before the bug was fixed this test would fail at least 30% of the time.
   */
   
  public void testTransitionRace() throws TimeoutException {
   for (int k = 0; k < 1000; k++) {
   List<Service> services = Lists.newArrayList();
   for (int i = 0; i < 5; i++) {
   services.add(new SnappyShutdownService(i));
   }
   ServiceManager manager = new ServiceManager(services);
   manager.startAsync().awaitHealthy();
   manager.stopAsync().awaitStopped(1, TimeUnit.SECONDS);
   }
   }
   
  /**
   * This service will shutdown very quickly after stopAsync is called and uses a background thread
   * so that we know that the stopping() listeners will execute on a different thread than the
   * terminated() listeners.
   */
   private static class SnappyShutdownService extends AbstractExecutionThreadService {
   final int index;
   final CountDownLatch latch = new CountDownLatch(1);
   
  SnappyShutdownService(int index) {
   this.index = index;
   }
   
  @Override protected void run() throws Exception {
   latch.await();
   }
   
  @Override protected void triggerShutdown() {
   latch.countDown();
   }
   
  @Override protected String serviceName() {
   return this.getClass().getSimpleName() + "[" + index + "]";
   }
   }
   
  public void testNulls() {
   ServiceManager manager = new ServiceManager(Arrays.<Service>asList());
   new NullPointerTester()
   .setDefault(ServiceManager.Listener.class, new RecordingListener())
   .testAllPublicInstanceMethods(manager);
   }
   
  private static final class RecordingListener extends ServiceManager.Listener {
   volatile boolean healthyCalled;
   volatile boolean stoppedCalled;
   final Set<Service> failedServices = Sets.newConcurrentHashSet();
   
  @Override public void healthy() {
   healthyCalled = true;
   }
   
  @Override public void stopped() {
   stoppedCalled = true;
   }
   
  @Override public void failure(Service service) {
   failedServices.add(service);
   }
   }
  }
  <pre>

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原文地址：https://www.cnblogs.com/muxi0407/p/12022079.html