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 can implement {@link #startUp}, {@link #run} and
026 * {@link #shutDown} methods. This class uses a single thread to execute the
027 * service; consider {@link AbstractService} if you would like to manage any
028 * threading manually.
029 *
030 * @author Jesse Wilson
031 * @since 1
032 */
033@Beta
034public abstract class AbstractExecutionThreadService implements Service {
035
036  /* use AbstractService for state management */
037  private final Service delegate = new AbstractService() {
038    @Override protected final void doStart() {
039      executor().execute(new Runnable() {
040        @Override
041        public void run() {
042          try {
043            startUp();
044            notifyStarted();
045
046            if (isRunning()) {
047              try {
048                AbstractExecutionThreadService.this.run();
049              } catch (Throwable t) {
050                try {
051                  shutDown();
052                } catch (Exception ignored) {}
053                throw t;
054              }
055            }
056
057            shutDown();
058            notifyStopped();
059          } catch (Throwable t) {
060            notifyFailed(t);
061            throw Throwables.propagate(t);
062          }
063        }
064      });
065    }
066
067    @Override protected void doStop() {
068      triggerShutdown();
069    }
070  };
071
072  /**
073   * Start the service. This method is invoked on the execution thread.
074   */
075  protected void startUp() throws Exception {}
076
077  /**
078   * Run the service. This method is invoked on the execution thread.
079   * Implementations must respond to stop requests. You could poll for lifecycle
080   * changes in a work loop:
081   * <pre>
082   *   public void run() {
083   *     while ({@link #isRunning()}) {
084   *       // perform a unit of work
085   *     }
086   *   }
087   * </pre>
088   * ...or you could respond to stop requests by implementing {@link
089   * #triggerShutdown()}, which should cause {@link #run()} to return.
090   */
091  protected abstract void run() throws Exception;
092
093  /**
094   * Stop the service. This method is invoked on the execution thread.
095   */
096  // TODO: consider supporting a TearDownTestCase-like API
097  protected void shutDown() throws Exception {}
098
099  /**
100   * Invoked to request the service to stop.
101   */
102  protected void triggerShutdown() {}
103
104  /**
105   * Returns the {@link Executor} that will be used to run this service.
106   * Subclasses may override this method to use a custom {@link Executor}, which
107   * may configure its worker thread with a specific name, thread group or
108   * priority. The returned executor's {@link Executor#execute(Runnable)
109   * execute()} method is called when this service is started, and should return
110   * promptly.
111   */
112  protected Executor executor() {
113    return new Executor() {
114      @Override
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 ListenableFuture<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 ListenableFuture<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}