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    import java.util.logging.Level;
024    import java.util.logging.Logger;
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 1.0
034     */
035    @Beta
036    public abstract class AbstractExecutionThreadService implements Service {
037      private static final Logger logger = Logger.getLogger(
038          AbstractExecutionThreadService.class.getName());
039    
040      /* use AbstractService for state management */
041      private final Service delegate = new AbstractService() {
042        @Override protected final void doStart() {
043          executor().execute(new Runnable() {
044            @Override
045            public void run() {
046              try {
047                startUp();
048                notifyStarted();
049    
050                if (isRunning()) {
051                  try {
052                    AbstractExecutionThreadService.this.run();
053                  } catch (Throwable t) {
054                    try {
055                      shutDown();
056                    } catch (Exception ignored) {
057                      logger.log(Level.WARNING,
058                          "Error while attempting to shut down the service"
059                          + " after failure.", ignored);
060                    }
061                    throw t;
062                  }
063                }
064    
065                shutDown();
066                notifyStopped();
067              } catch (Throwable t) {
068                notifyFailed(t);
069                throw Throwables.propagate(t);
070              }
071            }
072          });
073        }
074    
075        @Override protected void doStop() {
076          triggerShutdown();
077        }
078      };
079    
080      /**
081       * Constructor for use by subclasses.
082       */
083      protected AbstractExecutionThreadService() {}
084    
085      /**
086       * Start the service. This method is invoked on the execution thread.
087       *
088       * <p>By default this method does nothing.
089       */
090      protected void startUp() throws Exception {}
091    
092      /**
093       * Run the service. This method is invoked on the execution thread.
094       * Implementations must respond to stop requests. You could poll for lifecycle
095       * changes in a work loop:
096       * <pre>
097       *   public void run() {
098       *     while ({@link #isRunning()}) {
099       *       // perform a unit of work
100       *     }
101       *   }
102       * </pre>
103       * ...or you could respond to stop requests by implementing {@link
104       * #triggerShutdown()}, which should cause {@link #run()} to return.
105       */
106      protected abstract void run() throws Exception;
107    
108      /**
109       * Stop the service. This method is invoked on the execution thread.
110       *
111       * <p>By default this method does nothing.
112       */
113      // TODO: consider supporting a TearDownTestCase-like API
114      protected void shutDown() throws Exception {}
115    
116      /**
117       * Invoked to request the service to stop.
118       *
119       * <p>By default this method does nothing.
120       */
121      protected void triggerShutdown() {}
122    
123      /**
124       * Returns the {@link Executor} that will be used to run this service.
125       * Subclasses may override this method to use a custom {@link Executor}, which
126       * may configure its worker thread with a specific name, thread group or
127       * priority. The returned executor's {@link Executor#execute(Runnable)
128       * execute()} method is called when this service is started, and should return
129       * promptly.
130       *
131       * <p>The default implementation returns a new {@link Executor} that sets the
132       * name of its threads to the string returned by {@link #getServiceName}
133       */
134      protected Executor executor() {
135        return new Executor() {
136          @Override
137          public void execute(Runnable command) {
138            new Thread(command, getServiceName()).start();
139          }
140        };
141      }
142    
143      @Override public String toString() {
144        return getServiceName() + " [" + state() + "]";
145      }
146    
147      // We override instead of using ForwardingService so that these can be final.
148    
149      @Override public final ListenableFuture<State> start() {
150        return delegate.start();
151      }
152    
153      @Override public final State startAndWait() {
154        return delegate.startAndWait();
155      }
156    
157      @Override public final boolean isRunning() {
158        return delegate.isRunning();
159      }
160    
161      @Override public final State state() {
162        return delegate.state();
163      }
164    
165      @Override public final ListenableFuture<State> stop() {
166        return delegate.stop();
167      }
168    
169      @Override public final State stopAndWait() {
170        return delegate.stopAndWait();
171      }
172    
173      @Override public final void addListener(Listener listener, Executor executor) {
174        delegate.addListener(listener, executor);
175      }
176    
177      /**
178       * Returns the name of this service. {@link AbstractExecutionThreadService}
179       * may include the name in debugging output.
180       *
181       * <p>Subclasses may override this method.
182       *
183       * @since 10.0
184       */
185      protected String getServiceName() {
186        return getClass().getSimpleName();
187      }
188    }