//
   //  ========================================================================
   //  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.strategy;
  
  import java.util.concurrent.Executor;
  
  import org.eclipse.jetty.util.log.Log;
  import org.eclipse.jetty.util.log.Logger;
  import org.eclipse.jetty.util.thread.ExecutionStrategy;
  import org.eclipse.jetty.util.thread.Locker;
  
  /**
   * <p>A strategy where the caller thread iterates over task production, submitting each
   * task to an {@link Executor} for execution.</p>
   */
  public class ProduceConsume implements ExecutionStrategy, Runnable
  {
      private static final Logger LOG = Log.getLogger(ExecuteProduceConsume.class);
  
      private final Locker _locker = new Locker();
      private final Producer _producer;
      private final Executor _executor;
      private State _state = State.IDLE;
  
      public ProduceConsume(Producer producer, Executor executor)
      {
          this._producer = producer;
          this._executor = executor;
      }
  
      @Override
      public void execute()
      {
          try (Locker.Lock lock = _locker.lock())
          {
              switch(_state)
              {
                  case IDLE:
                      _state= State.PRODUCE;
                      break;
  
                  case PRODUCE:
                  case EXECUTE:
                      _state= State.EXECUTE;
                      return;
              }
          }
  
          // Iterate until we are complete.
          while (true)
          {
              // Produce a task.
              Runnable task = _producer.produce();
              if (LOG.isDebugEnabled())
                  LOG.debug("{} produced {}", _producer, task);
  
              if (task == null)
              {
                  try (Locker.Lock lock = _locker.lock())
                  {
                      switch(_state)
                      {
                          case IDLE:
                              throw new IllegalStateException();
                          case PRODUCE:
                              _state= State.IDLE;
                              return;
                          case EXECUTE:
                              _state= State.PRODUCE;
                              continue;
                      }
                  }
              }
  
              // Run the task.
              task.run();
          }
      }
  
      @Override
      public void dispatch()
      {
          _executor.execute(this);
     }
 
     @Override
     public void run()
     {
         execute();
     }
 
     public static class Factory implements ExecutionStrategy.Factory
     {
         @Override
         public ExecutionStrategy newExecutionStrategy(Producer producer, Executor executor)
         {
             return new ProduceConsume(producer, executor);
         }
     }
 
     private enum State
     {
         IDLE, PRODUCE, EXECUTE
     }
 }