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    }