    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 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 1.0
    032     */
    033    @Beta
    034    public 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      /**
    152       * Returns the name of this service. {@link AbstractExecutionThreadService} may include the name
    153       * in debugging output.
    154       *
    155       * <p>Subclasses may override this method.
    156       *
    157       * @since 10.0
    158       */
    159      protected String getServiceName() {
    160        return getClass().getSimpleName();
    161      }
    162    }