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
017package com.google.common.util.concurrent;
018
019import com.google.common.annotations.Beta;
020import com.google.common.base.Throwables;
021
022import 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
035public 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().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().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  /** Constructor for use by subclasses. */
069  protected AbstractIdleService() {}
070
071  /** Start the service. */
072  protected abstract void startUp() throws Exception;
073
074  /** Stop the service. */
075  protected abstract void shutDown() throws Exception;
076
077  /**
078   * Returns the {@link Executor} that will be used to run this service.
079   * Subclasses may override this method to use a custom {@link Executor}, which
080   * may configure its worker thread with a specific name, thread group or
081   * priority. The returned executor's {@link Executor#execute(Runnable)
082   * execute()} method is called when this service is started and stopped,
083   * and should return promptly.
084   */
085  protected Executor executor() {
086    final State state = state();
087    return new Executor() {
088      @Override
089      public void execute(Runnable command) {
090        MoreExecutors.newThread(serviceName() + " " + state, command).start();
091      }
092    };
093  }
094
095  @Override public String toString() {
096    return serviceName() + " [" + 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  /**
126   * @since 13.0
127   */
128  @Override public final void addListener(Listener listener, Executor executor) {
129    delegate.addListener(listener, executor);
130  }
131  
132  /**
133   * @since 14.0
134   */
135  @Override public final Throwable failureCause() {
136    return delegate.failureCause();
137  }
138  
139  /**
140   * Returns the name of this service. {@link AbstractIdleService} may include the name in debugging
141   * output.
142   *
143   * @since 14.0
144   */
145  protected String serviceName() {
146    return getClass().getSimpleName();
147  }
148}