Mailer.java

/* ************************************************************************* *
 *                                                                           *
 *        Copyright (c) 2012 Peter Cappello  <cappello@cs.ucsb.edu>          *
 *                                                                           *
 *    Permission is hereby granted, free of charge, to any person obtaining  *
 *  a copy of this software and associated documentation files (the          *
 *  "Software"), to deal in the Software without restriction, including      *
 *  without limitation the rights to use, copy, modify, merge, publish,      *
 *  distribute, sublicense, and/or sell copies of the Software, and to       *
 *  permit persons to whom the Software is furnished to do so, subject to    *
 *  the following conditions:                                                *
 *                                                                           *
 *    The above copyright notice and this permission notice shall be         *
 *  included in all copies or substantial portions of the Software.          *
 *                                                                           *
 *    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,        *
 *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF       *
 *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.   *
 *  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY     *
 *  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,     *
 *  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE        *
 *  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                   *
 *                                                                           *
 * ************************************************************************* */
/**
 * Encapsulates a List of Commands to be sent to a particular Service.
 *
 * @version 1.0
 * @author Peter Cappello
 */
package jicosfoundation;

import java.util.Iterator;
import java.util.Queue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class Mailer extends Processor
{

    private Service fromAddress;
    private Service toAddress;   // the destination of this Mail
    private Queue<Command> commandQ = new ConcurrentLinkedQueue<Command>();
    private BlockingQueue<Mailer> mailQ; // queue of references to this.
    private RemoteExceptionHandler remoteExceptionHandler;
    private Proxy myProxy;
    private final ReadWriteLock commandQLock = new ReentrantReadWriteLock();
    private final Lock r = commandQLock.readLock();
    private final Lock w = commandQLock.writeLock();

    public Mailer(Service fromAddress, RemoteExceptionHandler remoteExceptionHandler,
            BlockingQueue<Mailer> mailQ, Proxy myProxy)
    {
        super(mailQ, "Mailer");

        assert fromAddress != null;
        assert remoteExceptionHandler != null;

        this.fromAddress = fromAddress;
        this.remoteExceptionHandler = remoteExceptionHandler;
        this.mailQ = mailQ;
        this.myProxy = myProxy;
        toAddress = myProxy.getService();
    }

    /**
     * Add a Command to the list.
     *
     * @param command The Command object to be added.
     */
    public void add(Command command)
    {
        assert command != null;

        // synchronization is necessary to ensure add completes before copyCommandQ makes commandQ garbage.
        r.lock();
        try
        {
            commandQ.add(command);
        } finally
        {
            r.unlock();
        }
        try
        {
            mailQ.add(this); // notify mail processor: send commandQ
        } catch (Exception e)
        {
            e.printStackTrace();
        }
    }

    private Queue copyCommandQ()
    {
        Queue<Command> commandQCopy;
        Queue<Command> temp = new ConcurrentLinkedQueue<Command>();
        w.lock();
        try
        {
            commandQCopy = commandQ;
            commandQ = temp;
        } finally
        {
            w.unlock();
        }
        return commandQCopy;
    }

    /**
     * Mail command queue to destination distributed component
     */
    @Override
    void process(Object object)
    {
        if (commandQ.isEmpty())
        {
            return;
        }
        Queue<Command> commandQCopy = copyCommandQ();
        try
        {
            toAddress.receiveCommands(fromAddress, commandQCopy);
        } catch (Exception exception)
        {
            exception.printStackTrace();
            System.out.println("Mail: toAddress: " + toAddress + "\n Command Q: \n");
            for (Iterator iterator = commandQCopy.iterator(); iterator.hasNext();)
            {
                System.out.println(((Command) iterator.next()));
            }
            myProxy.evict();
            System.exit(1); // !! TODO modify when jPregel becomes fault-tolerant
            //remoteExceptionHandler.handle ( exception, fromAddress, toAddress );         
        }
    }

    /**
     * Returns a String representation of the object.
     *
     * @return A String representation of the object.
     */
    public String toString()
    {
        StringBuffer stringBuffer = new StringBuffer("Mail: toAddress: " + toAddress);
        stringBuffer.append("\n Command Q: \n");
        for (Iterator iterator = commandQ.iterator(); iterator.hasNext();)
        {
            stringBuffer.append(((Command) iterator.next()).toString());
        }
        return new String(stringBuffer);
    }
}