/**

  * Copyright 2009 Martin Vysny.

  *

  * This file is part of WebVM.

  *

  * WebVM is free software: you can redistribute it and/or modify

  * it under the terms of the GNU General Public License as published by

  * the Free Software Foundation, either version 3 of the License, or

  * (at your option) any later version.

  *

  * WebVM is distributed in the hope that it will be useful,

  * but WITHOUT ANY WARRANTY; without even the implied warranty of

  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

  * GNU General Public License for more details.

  *

  * You should have received a copy of the GNU General Public License

  * along with WebVM.  If not, see <http://www.gnu.org/licenses/>.

  */

 package sk.baka.webvm.misc;

 import java.util.concurrent.Executors;

 import java.util.concurrent.ScheduledExecutorService;

 import java.util.concurrent.ScheduledThreadPoolExecutor;

 import java.util.concurrent.ThreadFactory;

 import java.util.concurrent.atomic.AtomicInteger;

 /**

  * Executes various tasks in background thread.

  * @author Martin Vysny

  */

 public abstract class BackgroundService {

     /**

      * A short name of the service - used in thread names.

      */

     protected final String name;

     /**

      * Maximum thread pool size.

      */

     protected final int maxThreads;

     /**

      * Creates new service instance.

      * @param name A short name of the service - used in thread names.

      * @param maxThreads Maximum thread pool size.

      */

     protected BackgroundService(final String name, final int maxThreads) {

         this.name = name;

         this.maxThreads = maxThreads;

     }

     /**

      * Starts the sampling process in a background thread.

      */

     public synchronized void start() {

         if (executor != null) {

             throw new IllegalStateException("Already started.");

         }

         executor = new ScheduledThreadPoolExecutor(1, newDaemonFactory(name));

         started(executor);

     }

     private ScheduledExecutorService executor = null;

     /**

      * Invoked when the service is started.

      * @param executor executes tasks.

      */

     protected abstract void started(final ScheduledExecutorService executor);

     /**

      * Returns the executor.

      * @return the executor. null if not started.

      */

     protected synchronized final ScheduledExecutorService getExecutor() {

         return executor;

     }

     /**

      * Disposes of this sampler. This instance is no longer usable and cannot be started again.

      */

     public final synchronized void stop() {

         if (executor != null) {

             executor.shutdownNow();

             executor = null;

             stopped();

         }

     }

     /**

      * Invoked after the service has been stopped.

      */

     protected abstract void stopped();

     /**

      * Creates a new factory which creates daemon threads using the {@link Executors#defaultThreadFactory()}.

      * @param name create threads marked with this name.

      * @return a daemon thread factory.

      */

     public static ThreadFactory newDaemonFactory(final String name) {

         return new ThreadFactory() {

             private final ThreadFactory def = Executors.defaultThreadFactory();

             private final AtomicInteger threadNum = new AtomicInteger(0);

             public Thread newThread(Runnable r) {

                 final Thread result = def.newThread(r);

                 result.setName("WebVM: " + name + "-" + threadNum.incrementAndGet());

                 result.setDaemon(true);

                 return result;

             }

         };

     }

 }