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 com.google.common.annotations.Beta;
020 import com.google.common.base.Throwables;
021
022 import java.util.concurrent.Executor;
023
024 /**
025 * Base class for services that do not need a thread while "running"
026 * but may need one during startup and shutdown. Subclasses can
027 * implement {@link #startUp} and {@link #shutDown} methods, each
028 * which run in a executor which by default uses a separate thread
029 * for each method.
030 *
031 * @author Chris Nokleberg
032 * @since 1.0
033 */
034 @Beta
035 public abstract class AbstractIdleService implements Service {
036
037 /* use AbstractService for state management */
038 private final Service delegate = new AbstractService() {
039 @Override protected final void doStart() {
040 executor(State.STARTING).execute(new Runnable() {
041 @Override public void run() {
042 try {
043 startUp();
044 notifyStarted();
045 } catch (Throwable t) {
046 notifyFailed(t);
047 throw Throwables.propagate(t);
048 }
049 }
050 });
051 }
052
053 @Override protected final void doStop() {
054 executor(State.STOPPING).execute(new Runnable() {
055 @Override public void run() {
056 try {
057 shutDown();
058 notifyStopped();
059 } catch (Throwable t) {
060 notifyFailed(t);
061 throw Throwables.propagate(t);
062 }
063 }
064 });
065 }
066 };
067
068 /** Start the service. */
069 protected abstract void startUp() throws Exception;
070
071 /** Stop the service. */
072 protected abstract void shutDown() throws Exception;
073
074 /**
075 * Returns the {@link Executor} that will be used to run this service.
076 * Subclasses may override this method to use a custom {@link Executor}, which
077 * may configure its worker thread with a specific name, thread group or
078 * priority. The returned executor's {@link Executor#execute(Runnable)
079 * execute()} method is called when this service is started and stopped,
080 * and should return promptly.
081 *
082 * @param state {@link Service.State#STARTING} or
083 * {@link Service.State#STOPPING}, used by the default implementation for
084 * naming the thread
085 */
086 protected Executor executor(final State state) {
087 return new Executor() {
088 @Override
089 public void execute(Runnable command) {
090 new Thread(command, getServiceName() + " " + state).start();
091 }
092 };
093 }
094
095 @Override public String toString() {
096 return getServiceName() + " [" + state() + "]";
097 }
098
099 // We override instead of using ForwardingService so that these can be final.
100
101 @Override public final ListenableFuture<State> start() {
102 return delegate.start();
103 }
104
105 @Override public final State startAndWait() {
106 return delegate.startAndWait();
107 }
108
109 @Override public final boolean isRunning() {
110 return delegate.isRunning();
111 }
112
113 @Override public final State state() {
114 return delegate.state();
115 }
116
117 @Override public final ListenableFuture<State> stop() {
118 return delegate.stop();
119 }
120
121 @Override public final State stopAndWait() {
122 return delegate.stopAndWait();
123 }
124
125 private String getServiceName() {
126 return getClass().getSimpleName();
127 }
128 }