5.2-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：

• Service.State.NEW
• Service.State.STARTING
• Service.State.RUNNING
• Service.State.STOPPING
• Service.State.TERMINATED

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

 protected void startUp() {
dispatcher.listenForConnections(port, queue);
 }
 protected void run() {
   Connection connection;
   while ((connection = queue.take() != POISON)) {
     process(connection);
   }
 }
 protected void triggerShutdown() {
   dispatcher.stopListeningForConnections(queue);
   queue.put(POISON);
 }

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

</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 ![:(](http://ifeve.com/wp-includes/images/smilies/frownie.png) 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>