PriorityCommandQueue.java

/**
 * Copyright (c) 2010-2015, openHAB.org and others.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 */
package com.myhome.fcrisciani.queue;

import java.util.Vector;
import java.util.concurrent.Semaphore;

/**
 * This class implements 3 priority queues of Open commands to be sent
 *
 * @author Flavio Crisciani
 * @serial 1.0
 * @since 1.7.0
 */
public class PriorityCommandQueue {

    // ----- TYPES ----- //

    // ---- MEMBERS ---- //

    final Vector<String> level1 = new Vector<String>();
    final Vector<String> level2 = new Vector<String>();
    final Vector<String> level3 = new Vector<String>();

    final Semaphore commandsAvailable = new Semaphore(0);

    // ---- METHODS ---- //
    /**
     * Add a command to the high priority queue
     * 
     * @param c
     *            command to queue
     * @return true if correctly queued
     */
    public void addHighLevel(String c) {
        this.level1.add(c);
        commandsAvailable.release();
    }

    /**
     * Add a command to the medium priority queue
     * 
     * @param c
     *            command to queue
     * @return true if correctly queued
     */
    public void addMediumLevel(String c) {
        this.level2.add(c);
        commandsAvailable.release();
    }

    /**
     * Add a command to the low priority queue
     * 
     * @param c
     *            command to queue
     * @return true if correctly queued
     */
    public void addLowLevel(String c) {
        this.level3.add(c);
        commandsAvailable.release();
    }

    /**
     * Get a command, when available from one of the queue, if they are all
     * empty it suspend the thread on a semaphone
     * 
     * @return the command to execute
     */
    public String getCommand() {
        String resultCommand = null;
        try {
            if (commandsAvailable.availablePermits() == 0) {
                // System.out.println("CommandTail: Non ci sono comandi da eseguire nelle code mi sospendo");
            }
            commandsAvailable.acquire();
        } catch (InterruptedException e) {
            System.err.println("PriorityCommandQueue: Exception during suspetion on the semaphore: " + e.toString());
            resultCommand = null;
        }
        if (level1.size() > 0) {
            resultCommand = level1.remove(0);
        } else if (level2.size() > 0) {
            resultCommand = level2.remove(0);
        } else if (level3.size() > 0) {
            resultCommand = level3.remove(0);
        }

        return resultCommand;
    }

    /**
     * Returns number of commands available
     * 
     * @return the number of command available
     */
    public int numCommands() {
        return commandsAvailable.availablePermits();
    }

}