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        
040        @Override
041        protected final void doStart() {
042          executor(State.STARTING).execute(new Runnable() {
043            public void run() {
044              try {
045                startUp();
046                notifyStarted();
047              } catch (Throwable t) {
048                notifyFailed(t);
049                throw Throwables.propagate(t);
050              }
051            }
052          });
053        }
054    
055        
056        @Override
057        protected final void doStop() {
058          executor(State.STOPPING).execute(new Runnable() {
059            public void run() {
060              try {
061                shutDown();
062                notifyStopped();
063              } catch (Throwable t) {
064                notifyFailed(t);
065                throw Throwables.propagate(t);
066              }
067            }
068          });
069        }
070      };
071    
072      /** Start the service. */
073      protected abstract void startUp() throws Exception;
074    
075      /** Stop the service. */
076      protected abstract void shutDown() throws Exception;
077    
078      /**
079       * Returns the {@link Executor} that will be used to run this service.
080       * Subclasses may override this method to use a custom {@link Executor}, which
081       * may configure its worker thread with a specific name, thread group or
082       * priority. The returned executor's {@link Executor#execute(Runnable)
083       * execute()} method is called when this service is started and stopped,
084       * and should return promptly.
085       *
086       * @param state {@link Service.State#STARTING} or
087       *     {@link Service.State#STOPPING}, used by the default implementation for
088       *     naming the thread
089       */
090      protected Executor executor(final State state) {
091        return new Executor() {
092          public void execute(Runnable command) {
093            new Thread(command, getServiceName() + " " + state).start();
094          }
095        };
096      }
097    
098      
099      @Override
100      public String toString() {
101        return getServiceName() + " [" + state() + "]";
102      }
103    
104      // We override instead of using ForwardingService so that these can be final.
105    
106      public final ListenableFuture<State> start() {
107        return delegate.start();
108      }
109    
110      public final State startAndWait() {
111        return delegate.startAndWait();
112      }
113    
114      public final boolean isRunning() {
115        return delegate.isRunning();
116      }
117    
118      public final State state() {
119        return delegate.state();
120      }
121    
122      public final ListenableFuture<State> stop() {
123        return delegate.stop();
124      }
125    
126      public final State stopAndWait() {
127        return delegate.stopAndWait();
128      }
129    
130      public final void addListener(Listener listener, Executor executor) {
131        delegate.addListener(listener, executor);
132      }
133    
134      private String getServiceName() {
135        return getClass().getSimpleName();
136      }
137    }