    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    }