content: /**
   * This file is part of Aion-Lightning <aion-lightning.org>.
   *
   *  Aion-Lightning 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.
   *
   *  Aion-Lightning 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 Aion-Lightning.
   *  If not, see <http://www.gnu.org/licenses/>.
   */
  package com.aionemu.gameserver.taskmanager;
  
  import java.util.concurrent.locks.ReentrantLock;
  
  import com.aionemu.gameserver.utils.ThreadPoolManager;
  
  /**
   * @author NB4L1
   */
  public abstract class FIFOExecutableQueue implements Runnable {
  
  	private static final byte NONE = 0;
  	private static final byte QUEUED = 1;
  	private static final byte RUNNING = 2;
  	private final ReentrantLock lock = new ReentrantLock();
  	private volatile byte state = NONE;
  
  	protected final void execute() {
  		lock();
  		try {
  			if (state != NONE) {
  				return;
  			}
  
  			state = QUEUED;
  		}
  		finally {
  			unlock();
  		}
  
  		ThreadPoolManager.getInstance().execute(this);
  	}
  
  	public final void lock() {
  		lock.lock();
  	}
  
  	public final void unlock() {
  		lock.unlock();
  	}
  
  	@Override
  	public final void run() {
  		try {
  			while (!isEmpty()) {
  				setState(QUEUED, RUNNING);
  
  				try {
  					while (!isEmpty()) {
  						removeAndExecuteFirst();
  					}
  				}
  				finally {
  					setState(RUNNING, QUEUED);
  				}
  			}
  		}
  		finally {
  			setState(QUEUED, NONE);
  		}
  	}
  
  	private void setState(byte expected, byte value) {
  		lock();
  		try {
  			if (state != expected) {
  				throw new IllegalStateException("state: " + state + ", expected: " + expected);
  			}
  		}
  		finally {
  			state = value;
  
  			unlock();
  		}
  	}
  
  	protected abstract boolean isEmpty();
  
  	protected abstract void removeAndExecuteFirst();
  }
  