    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 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
    035    public 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(State.STARTING).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(State.STOPPING).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      /** Start the service. */
    069      protected abstract void startUp() throws Exception;
    070
    071      /** Stop the service. */
    072      protected abstract void shutDown() throws Exception;
    073
    074      /**
    075       * Returns the {@link Executor} that will be used to run this service.
    076       * Subclasses may override this method to use a custom {@link Executor}, which
    077       * may configure its worker thread with a specific name, thread group or
    078       * priority. The returned executor's {@link Executor#execute(Runnable)
    079       * execute()} method is called when this service is started and stopped,
    080       * and should return promptly.
    081       *
    082       * @param state {@link Service.State#STARTING} or
    083       *     {@link Service.State#STOPPING}, used by the default implementation for
    084       *     naming the thread
    085       */
    086      protected Executor executor(final State state) {
    087        return new Executor() {
    088          @Override
    089          public void execute(Runnable command) {
    090            new Thread(command, getServiceName() + " " + state).start();
    091          }
    092        };
    093      }
    094
    095      @Override public String toString() {
    096        return getServiceName() + " [" + 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      private String getServiceName() {
    126        return getClass().getSimpleName();
    127      }
    128    }