//
   //  ========================================================================
   //  Copyright (c) 1995-2016 Mort Bay Consulting Pty. Ltd.
   //  ------------------------------------------------------------------------
   //  All rights reserved. This program and the accompanying materials
   //  are made available under the terms of the Eclipse Public License v1.0
   //  and Apache License v2.0 which accompanies this distribution.
   //
   //      The Eclipse Public License is available at
  //      http://www.eclipse.org/legal/epl-v10.html
  //
  //      The Apache License v2.0 is available at
  //      http://www.opensource.org/licenses/apache2.0.php
  //
  //  You may elect to redistribute this code under either of these licenses.
  //  ========================================================================
  //
  
  package org.eclipse.jetty.util.thread;
  
  import java.io.IOException;
  import java.util.Arrays;
  import java.util.List;
  import java.util.concurrent.ScheduledFuture;
  import java.util.concurrent.ScheduledThreadPoolExecutor;
  import java.util.concurrent.ThreadFactory;
  import java.util.concurrent.TimeUnit;
  
  import org.eclipse.jetty.util.component.AbstractLifeCycle;
  import org.eclipse.jetty.util.component.ContainerLifeCycle;
  import org.eclipse.jetty.util.component.Dumpable;
  
  /**
   * Implementation of {@link Scheduler} based on JDK's {@link ScheduledThreadPoolExecutor}.
   * <p>
   * While use of {@link ScheduledThreadPoolExecutor} creates futures that will not be used,
   * it has the advantage of allowing to set a property to remove cancelled tasks from its
   * queue even if the task did not fire, which provides a huge benefit in the performance
   * of garbage collection in young generation.
   */
  public class ScheduledExecutorScheduler extends AbstractLifeCycle implements Scheduler, Dumpable
  {
      private final String name;
      private final boolean daemon;
      private final ClassLoader classloader;
      private final ThreadGroup threadGroup;
      private volatile ScheduledThreadPoolExecutor scheduler;
      private volatile Thread thread;
  
      public ScheduledExecutorScheduler()
      {
          this(null, false);
      }  
  
      public ScheduledExecutorScheduler(String name, boolean daemon)
      {
          this (name,daemon, Thread.currentThread().getContextClassLoader());
      }
      
      public ScheduledExecutorScheduler(String name, boolean daemon, ClassLoader threadFactoryClassLoader)
      {
          this(name, daemon, threadFactoryClassLoader, null);
      }
  
      public ScheduledExecutorScheduler(String name, boolean daemon, ClassLoader threadFactoryClassLoader, ThreadGroup threadGroup)
      {
          this.name = name == null ? "Scheduler-" + hashCode() : name;
          this.daemon = daemon;
          this.classloader = threadFactoryClassLoader == null ? Thread.currentThread().getContextClassLoader() : threadFactoryClassLoader;
          this.threadGroup = threadGroup;
      }
  
      @Override
      protected void doStart() throws Exception
      {
          scheduler = new ScheduledThreadPoolExecutor(1, new ThreadFactory()
          {
              @Override
              public Thread newThread(Runnable r)
              {
                  Thread thread = ScheduledExecutorScheduler.this.thread = new Thread(threadGroup, r, name);
                  thread.setDaemon(daemon);
                  thread.setContextClassLoader(classloader);
                  return thread;
              }
          });
          scheduler.setRemoveOnCancelPolicy(true);
          super.doStart();
      }
  
      @Override
      protected void doStop() throws Exception
      {
          scheduler.shutdownNow();
          super.doStop();
          scheduler = null;
      }
  
      @Override
     public Task schedule(Runnable task, long delay, TimeUnit unit)
     {
         ScheduledThreadPoolExecutor s = scheduler;
         if (s==null)
             return new Task(){
                 @Override
                 public boolean cancel()
                 {
                     return false;
                 }};
 
         ScheduledFuture<?> result = s.schedule(task, delay, unit);
         return new ScheduledFutureTask(result);
     }
 
     @Override
     public String dump()
     {
         return ContainerLifeCycle.dump(this);
     }
 
     @Override
     public void dump(Appendable out, String indent) throws IOException
     {
         ContainerLifeCycle.dumpObject(out, this);
         Thread thread = this.thread;
         if (thread != null)
         {
             List<StackTraceElement> frames = Arrays.asList(thread.getStackTrace());
             ContainerLifeCycle.dump(out, indent, frames);
         }
     }
 
     private static class ScheduledFutureTask implements Task
     {
         private final ScheduledFuture<?> scheduledFuture;
 
         ScheduledFutureTask(ScheduledFuture<?> scheduledFuture)
         {
             this.scheduledFuture = scheduledFuture;
         }
 
         @Override
         public boolean cancel()
         {
             return scheduledFuture.cancel(false);
         }
     }
 }