Google Guava官方教程（中文版）

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

/
  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 > void assertLessThan(T a, T b) {
 if (a.compareTo(b) >= 0) {
 fail(String.format("Expected %s to be less than %s", a, b));
 }
 }
}

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 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();
 }
 }
}

AbstractScheduledServiceTest

/
  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);
 }};
 }
 }
 }
}

AbstractServiceTest

/
  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 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 stateHistory = Lists.newArrayList();
 final CountDownLatch completionLatch = new CountDownLatch(1);

ImmutableList 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();
}

ServiceManagerTest

/
  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 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 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.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 start() {
 return delegate.start();
 }

@Override public final ListenableFuture 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.
 
  
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 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.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 failedServices = Sets.newConcurrentHashSet();

@Override public void healthy() {
 healthyCalled = true;
 }

@Override public void stopped() {
 stoppedCalled = true;
 }

@Override public void failure(Service service) {
 failedServices.add(service);
 }
 }
}