001 /*
002 * Copyright (C) 2009 The Guava Authors
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 static com.google.common.base.Preconditions.checkNotNull;
020
021 import com.google.common.annotations.Beta;
022 import com.google.common.util.concurrent.Service.State; // javadoc needs this
023
024 import java.util.concurrent.ExecutionException;
025 import java.util.concurrent.TimeUnit;
026 import java.util.concurrent.TimeoutException;
027 import java.util.concurrent.locks.ReentrantLock;
028
029 /**
030 * Base class for implementing services that can handle {@link #doStart} and
031 * {@link #doStop} requests, responding to them with {@link #notifyStarted()}
032 * and {@link #notifyStopped()} callbacks. Its subclasses must manage threads
033 * manually; consider {@link AbstractExecutionThreadService} if you need only a
034 * single execution thread.
035 *
036 * @author Jesse Wilson
037 * @since 1.0
038 */
039 @Beta
040 public abstract class AbstractService implements Service {
041
042 private final ReentrantLock lock = new ReentrantLock();
043
044 private final Transition startup = new Transition();
045 private final Transition shutdown = new Transition();
046
047 /**
048 * The internal state, which equals external state unless
049 * shutdownWhenStartupFinishes is true. Guarded by {@code lock}.
050 */
051 private State state = State.NEW;
052
053 /**
054 * If true, the user requested a shutdown while the service was still starting
055 * up. Guarded by {@code lock}.
056 */
057 private boolean shutdownWhenStartupFinishes = false;
058
059 /**
060 * This method is called by {@link #start} to initiate service startup. The
061 * invocation of this method should cause a call to {@link #notifyStarted()},
062 * either during this method's run, or after it has returned. If startup
063 * fails, the invocation should cause a call to {@link
064 * #notifyFailed(Throwable)} instead.
065 *
066 * <p>This method should return promptly; prefer to do work on a different
067 * thread where it is convenient. It is invoked exactly once on service
068 * startup, even when {@link #start} is called multiple times.
069 */
070 protected abstract void doStart();
071
072 /**
073 * This method should be used to initiate service shutdown. The invocation
074 * of this method should cause a call to {@link #notifyStopped()}, either
075 * during this method's run, or after it has returned. If shutdown fails, the
076 * invocation should cause a call to {@link #notifyFailed(Throwable)} instead.
077 *
078 * <p>This method should return promptly; prefer to do work on a different
079 * thread where it is convenient. It is invoked exactly once on service
080 * shutdown, even when {@link #stop} is called multiple times.
081 */
082 protected abstract void doStop();
083
084 @Override
085 public final ListenableFuture<State> start() {
086 lock.lock();
087 try {
088 if (state == State.NEW) {
089 state = State.STARTING;
090 doStart();
091 }
092 } catch (Throwable startupFailure) {
093 // put the exception in the future, the user can get it via Future.get()
094 notifyFailed(startupFailure);
095 } finally {
096 lock.unlock();
097 }
098
099 return startup;
100 }
101
102 @Override
103 public final ListenableFuture<State> stop() {
104 lock.lock();
105 try {
106 if (state == State.NEW) {
107 state = State.TERMINATED;
108 startup.set(State.TERMINATED);
109 shutdown.set(State.TERMINATED);
110 } else if (state == State.STARTING) {
111 shutdownWhenStartupFinishes = true;
112 startup.set(State.STOPPING);
113 } else if (state == State.RUNNING) {
114 state = State.STOPPING;
115 doStop();
116 }
117 } catch (Throwable shutdownFailure) {
118 // put the exception in the future, the user can get it via Future.get()
119 notifyFailed(shutdownFailure);
120 } finally {
121 lock.unlock();
122 }
123
124 return shutdown;
125 }
126
127 @Override
128 public State startAndWait() {
129 return Futures.getUnchecked(start());
130 }
131
132 @Override
133 public State stopAndWait() {
134 return Futures.getUnchecked(stop());
135 }
136
137 /**
138 * Implementing classes should invoke this method once their service has
139 * started. It will cause the service to transition from {@link
140 * State#STARTING} to {@link State#RUNNING}.
141 *
142 * @throws IllegalStateException if the service is not
143 * {@link State#STARTING}.
144 */
145 protected final void notifyStarted() {
146 lock.lock();
147 try {
148 if (state != State.STARTING) {
149 IllegalStateException failure = new IllegalStateException(
150 "Cannot notifyStarted() when the service is " + state);
151 notifyFailed(failure);
152 throw failure;
153 }
154
155 state = State.RUNNING;
156 if (shutdownWhenStartupFinishes) {
157 stop();
158 } else {
159 startup.set(State.RUNNING);
160 }
161 } finally {
162 lock.unlock();
163 }
164 }
165
166 /**
167 * Implementing classes should invoke this method once their service has
168 * stopped. It will cause the service to transition from {@link
169 * State#STOPPING} to {@link State#TERMINATED}.
170 *
171 * @throws IllegalStateException if the service is neither {@link
172 * State#STOPPING} nor {@link State#RUNNING}.
173 */
174 protected final void notifyStopped() {
175 lock.lock();
176 try {
177 if (state != State.STOPPING && state != State.RUNNING) {
178 IllegalStateException failure = new IllegalStateException(
179 "Cannot notifyStopped() when the service is " + state);
180 notifyFailed(failure);
181 throw failure;
182 }
183
184 state = State.TERMINATED;
185 shutdown.set(State.TERMINATED);
186 } finally {
187 lock.unlock();
188 }
189 }
190
191 /**
192 * Invoke this method to transition the service to the
193 * {@link State#FAILED}. The service will <b>not be stopped</b> if it
194 * is running. Invoke this method when a service has failed critically or
195 * otherwise cannot be started nor stopped.
196 */
197 protected final void notifyFailed(Throwable cause) {
198 checkNotNull(cause);
199
200 lock.lock();
201 try {
202 if (state == State.STARTING) {
203 startup.setException(cause);
204 shutdown.setException(new Exception(
205 "Service failed to start.", cause));
206 } else if (state == State.STOPPING) {
207 shutdown.setException(cause);
208 }
209
210 state = State.FAILED;
211 } finally {
212 lock.unlock();
213 }
214 }
215
216 @Override
217 public final boolean isRunning() {
218 return state() == State.RUNNING;
219 }
220
221 @Override
222 public final State state() {
223 lock.lock();
224 try {
225 if (shutdownWhenStartupFinishes && state == State.STARTING) {
226 return State.STOPPING;
227 } else {
228 return state;
229 }
230 } finally {
231 lock.unlock();
232 }
233 }
234
235 @Override public String toString() {
236 return getClass().getSimpleName() + " [" + state() + "]";
237 }
238
239 /**
240 * A change from one service state to another, plus the result of the change.
241 */
242 private class Transition extends AbstractFuture<State> {
243 @Override
244 public State get(long timeout, TimeUnit unit)
245 throws InterruptedException, TimeoutException, ExecutionException {
246 try {
247 return super.get(timeout, unit);
248 } catch (TimeoutException e) {
249 throw new TimeoutException(AbstractService.this.toString());
250 }
251 }
252 }
253 }