001 /*
002 * Copyright (C) 2009 Google Inc.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package com.google.common.util.concurrent;
018
019 import com.google.common.annotations.Beta;
020 import com.google.common.base.Service;
021 import com.google.common.base.Throwables;
022
023 import java.util.concurrent.Executor;
024 import java.util.concurrent.Future;
025
026 /**
027 * Base class for services that can implement {@link #startUp}, {@link #run} and
028 * {@link #shutDown} methods. This class uses a single thread to execute the
029 * service; consider {@link AbstractService} if you would like to manage any
030 * threading manually.
031 *
032 * @author Jesse Wilson
033 * @since 1
034 */
035 @Beta
036 public abstract class AbstractExecutionThreadService implements Service {
037
038 /* use AbstractService for state management */
039 private final Service delegate = new AbstractService() {
040 @Override protected final void doStart() {
041 executor().execute(new Runnable() {
042 public void run() {
043 try {
044 startUp();
045 notifyStarted();
046
047 if (isRunning()) {
048 try {
049 AbstractExecutionThreadService.this.run();
050 } catch (Throwable t) {
051 try {
052 shutDown();
053 } catch (Exception ignored) {}
054 throw t;
055 }
056 }
057
058 shutDown();
059 notifyStopped();
060 } catch (Throwable t) {
061 notifyFailed(t);
062 throw Throwables.propagate(t);
063 }
064 }
065 });
066 }
067
068 @Override protected void doStop() {
069 triggerShutdown();
070 }
071 };
072
073 /**
074 * Start the service. This method is invoked on the execution thread.
075 */
076 protected void startUp() throws Exception {}
077
078 /**
079 * Run the service. This method is invoked on the execution thread.
080 * Implementations must respond to stop requests. You could poll for lifecycle
081 * changes in a work loop:
082 * <pre>
083 * public void run() {
084 * while ({@link #isRunning()}) {
085 * // perform a unit of work
086 * }
087 * }
088 * </pre>
089 * ...or you could respond to stop requests by implementing {@link
090 * #triggerShutdown()}, which should cause {@link #run()} to return.
091 */
092 protected abstract void run() throws Exception;
093
094 /**
095 * Stop the service. This method is invoked on the execution thread.
096 */
097 // TODO: consider supporting a TearDownTestCase-like API
098 protected void shutDown() throws Exception {}
099
100 /**
101 * Invoked to request the service to stop.
102 */
103 protected void triggerShutdown() {}
104
105 /**
106 * Returns the {@link Executor} that will be used to run this service.
107 * Subclasses may override this method to use a custom {@link Executor}, which
108 * may configure its worker thread with a specific name, thread group or
109 * priority. The returned executor's {@link Executor#execute(Runnable)
110 * execute()} method is called when this service is started, and should return
111 * promptly.
112 */
113 protected Executor executor() {
114 return new Executor() {
115 public void execute(Runnable command) {
116 new Thread(command, getServiceName()).start();
117 }
118 };
119 }
120
121 @Override public String toString() {
122 return getServiceName() + " [" + state() + "]";
123 }
124
125 // We override instead of using ForwardingService so that these can be final.
126
127 @Override public final Future<State> start() {
128 return delegate.start();
129 }
130
131 @Override public final State startAndWait() {
132 return delegate.startAndWait();
133 }
134
135 @Override public final boolean isRunning() {
136 return delegate.isRunning();
137 }
138
139 @Override public final State state() {
140 return delegate.state();
141 }
142
143 @Override public final Future<State> stop() {
144 return delegate.stop();
145 }
146
147 @Override public final State stopAndWait() {
148 return delegate.stopAndWait();
149 }
150
151 private String getServiceName() {
152 return getClass().getSimpleName();
153 }
154 }