import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

import java.awt.image.BufferedImage;
import java.util.concurrent.LinkedBlockingQueue;

/**
 * This demo program divides up a large computation into a fairly
 * large number of smaller tasks.  The computation is to compute
 * an image, and each task computes one row of pixels in the image.
 * 
 * A thread pool is created at the beginning of the program, with
 * one thread for each available processor.  The threads remove
 * tasks from a blocking queue and execute them.  The threads never
 * terminate (until the program ends).  To start a computation, tasks
 * are created and added to the blocking queue.  As soon as the 
 * first tasks are added to the queue, the threads "wake up" and
 * start working on them.
 * 
 * (The image is a small piece of the famous Mandelbrot set,
 *  which is used just because it takes some time to compute.  
 * There is no need to understand what the image means.)  
 */
public class MultiprocessingDemo3 extends JPanel {

    /**
     * This main routine just shows a panel of type MultiprocessingDemo3.
     */
    public static void main(String[] args) {
        JFrame window = new JFrame("Multiprocessing Demo 3");
        MultiprocessingDemo3 content = new MultiprocessingDemo3();
        window.setContentPane(content);
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.pack();
        window.setResizable(false);
        Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
        if (window.getWidth() > screenSize.width-100 || window.getHeight() > screenSize.height-100) {
            double scale1 = (double)(screenSize.width-100)/window.getWidth();
            double scale2 = (double)(screenSize.height-100)/window.getHeight();
            double scale = Math.min(scale1,scale2);
            window.setSize( (int)(scale*window.getWidth()), (int)(scale*window.getHeight()) );
        }
        window.setLocation( (screenSize.width - window.getWidth()) / 2,
                (screenSize.height - window.getHeight()) / 2 );
        window.setVisible(true);
    }


    private WorkerThread[] workers;  // The thread pool.  Note:  The threads are created in
                                     // the start() method, the first time the user clicks the
                                     // "Start" button.  They continue to exist until the
                                     // program ends.

    private LinkedBlockingQueue<Runnable> taskQueue;  // The queue that holds individual tasks;

    private volatile int jobNumber; // Job number of the current computation job.
                                    // This is incremented after the job has completed.
                                    // Note that any left-over tasks from a job are ignored
                                    // when they finally complete.  This can happen when the
                                    // user aborts a computation, since if a thread is working
                                    // on a task when that happens, it will continue to work
                                    // that task until the task completes, so the task can
                                    // complete after the job of which it is a part has been
                                    // aborted.  (Note:  The task itself could check the current
                                    // job number as it is running and terminate early if the
                                    // job number has changed.  This would make sense if the
                                    // task's computation were very long.)

    private int taskCount;  // The number of tasks that make up one computation job.
    private volatile int tasksCompleted; // How many tasks in the current job have finished?

    private volatile boolean jobInProgress; // Set to true when a job starts, false when it ends.

    private JButton startButton; // Button the user can click to start or abort the thread.
    private BufferedImage image; // Contains the image that is computed by this program.
    int[] palette;  // Holds a spectrum of RGB color values; used in computing pixel colors.


    /**
     * The display is a JPanel that shows the image.  The part of the image that has
     * not yet been computed is gray.  If the image has not yet been created, the
     * entire display is filled with gray.
     */
    private JPanel display = new JPanel() {
        protected void paintComponent(Graphics g) {
            if (image == null)
                super.paintComponent(g);  // fill with background color, gray
            else {
                /* Copy the image onto the display.  This is synchronized because
                 * there are several threads that compete for access to the image:
                 * the threads that compute the image and the thread that does the
                 * painting.  All synchronization is done on the main class object,
                 * referred to here as MultiprocessingDemo3.this.
                 */
                synchronized(MultiprocessingDemo3.this) {
                    g.drawImage(image,0,0,null);
                }
            }
        }
    };


    /**
     * Constructor creates a panel to hold the display, with a "Start" button 
     * and a pop-up menu for selecting the number of threads below it.
     */
    public MultiprocessingDemo3() {
        display.setPreferredSize(new Dimension(1600,1200));
        display.setBackground(Color.LIGHT_GRAY);
        setBorder(BorderFactory.createLineBorder(Color.BLACK, 1));
        setLayout(new BorderLayout());
        add(display, BorderLayout.CENTER);
        JPanel bottom = new JPanel();
        startButton = new JButton("Start");
        bottom.add(startButton);
        bottom.setBackground(Color.WHITE);
        add(bottom,BorderLayout.SOUTH);
        palette = new int[256];
        for (int i = 0; i < 256; i++)
            palette[i] = Color.getHSBColor(i/255F, 1, 1).getRGB();
        startButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (jobInProgress)
                    stop();
                else
                    start();
            }
        });
        taskQueue = new LinkedBlockingQueue<Runnable>();
    }


    /**
     * This method is called when the user clicks the Start button,
     * while no computation is in progress.  It clears the image
     * and sets up the computation of a new image.  The first time
     * that it is called, it is also responsible for creating the
     * image and the thread pool.
     */
    synchronized private void start() {
        startButton.setText("Abort"); // change name while computation is in progress
        int width = display.getWidth() + 2;
        int height = display.getHeight() + 2;
        if (image == null) { // create the image and the thread pool
            image = new BufferedImage(width,height,BufferedImage.TYPE_INT_ARGB);
            int processors = Runtime.getRuntime().availableProcessors();
            workers = new WorkerThread[processors];
            for (int i = 0; i < processors; i++) {
                workers[i] = new WorkerThread();
            }
        }
        Graphics g = image.getGraphics();  // fill image with gray
        g.setColor(Color.LIGHT_GRAY);
        g.fillRect(0,0,width,height);
        g.dispose();
        display.repaint();

        double xmin = -1.6744096740931858;
        double xmax = -1.674409674093473;
        double ymin = 4.716540768697223E-5;
        double ymax = 4.716540790246652E-5;
        int maxIterations = 10000;
        double dx = (xmax-xmin)/(width-1);
        double dy = (ymax-ymin)/(height-1);
        for (int row = 0; row < height; row++) { // Add tasks for current job to job queue.
            double y = ymax - row*dy;
            MandelbrotTask task = new MandelbrotTask(jobNumber, row, width, maxIterations, xmin, y, dx);
            taskQueue.add(task);
        }
        tasksCompleted = 0;
        taskCount = height;
        jobInProgress = true;
    }


    /**
     * This method is called when the user clicks the button while
     * a thread is running.  It is also called by the taskFinished()
     * method when all the tasks that make up a job have been
     * completed.  The responsibility of this method is to
     * finish the current job by incrementing the jobNumber and
     * discarding any tasks from the current job that are still in
     * the queue (in case the job is ending because the user has
     * aborted it before it finished).
     */
    synchronized private void stop() {
        startButton.setText("Start Again");
        taskQueue.clear();
        jobNumber++;
        jobInProgress = false;
    }


    /**
     * This method is called by each thread when it terminates.  We keep track
     * of the number of threads that have terminated, so that when they have
     * all finished, we can put the program into the correct state, such as
     * changing the name of the button to "Start Again" and re-enabling the
     * pop-up menu.
     */
    synchronized private void taskFinished(MandelbrotTask task) {
        if (task.jobNumber != jobNumber) {
            System.out.println("Dropping results from previous job."); // for testing
            return;
        }
        tasksCompleted++;
        image.setRGB(0,task.rowNumber, task.width, 1, task.rgb, 0, task.width);
        display.repaint(0,task.rowNumber,task.width,1); // Repaint just the newly computed row.
        if (tasksCompleted == taskCount) { // all threads have finished
            stop();
        }
    }


    /**
     * An object of type MandelbrotTask represents the task of computing one row
     * of pixels in an image of the Mandelbrot set.  The task has a run() method
     * that does the actual computation.  It also calls the taskFinished() method
     * before terminating.
     */
    private class MandelbrotTask implements Runnable {
        int jobNumber;  // Which job is this task part of?
        int rowNumber;  // Which row of pixels does this task compute?
        double xmin;    // The x-value for the first pixel in the row.
        double y;       // The y-value for all the pixels in the row.
        double dx;      // The change in x-value from one pixel to the next.
        int width;      // The number of pixels in the row.
        int maxIterations;  // The maximum count in the Mandelbrot algorithm.
        int[] rgb;      // The pixel colors computed by this task;
        MandelbrotTask( int jobNumber, int rowNumber, int width, int maxIterations, double xmin, double y, double dx) {
            this.jobNumber = jobNumber;
            this.rowNumber = rowNumber;
            this.maxIterations = maxIterations;
            this.xmin = xmin;
            this.y = y;
            this.dx = dx;
            this.width = width;
        }
        public void run() {
            rgb= new int[width];     // The colors computed for the pixels.
            for (int i = 0; i < rgb.length; i++) {
                double x = xmin + i * dx;
                int count = 0;
                double xx = x;
                double yy = y;
                while (count < maxIterations && (xx*xx + yy*yy) < 4) {
                    count++;
                    double newxx = xx*xx - yy*yy + x;
                    yy = 2*xx*yy + y;
                    xx = newxx; 
                }
                if (count == maxIterations)
                    rgb[i] = 0;
                else
                    rgb[i] = palette[count % 256];
            }
            taskFinished(this);
        }
    }


    /**
     * This class defines the worker threads that make up the thread pool.
     * A WorkerThread runs in a loop in which it retrieves a task from the 
     * taskQueue and calls the run() method in that task.  Note that if
     * the queue is empty, the thread blocks until a task becomes available
     * in the queue.  The constructor starts the thread, so there is no
     * need for the main program to do so.  The thread will run at a priority
     * that is one less than the priority of the thread that calls the
     * constructor.
     * 
     * A WorkerThread is designed to run in an infinite loop.  It will
     * end only when the Java virtual machine exits. (This assumes that
     * the tasks that are executed don't throw exceptions, which is true
     * in this program.)  The constructor sets the thread to run as
     * a daemon thread; the Java virtual machine will exit when the
     * only threads are daemon threads.  (In this program, this is not
     * necessary since the virtual machine is set to exit when the
     * window is closed.  In a multi-window program, however, that would
     * not be the case and it would be important for the threads to be
     * daemon threads.)
     */
    private class WorkerThread extends Thread {
        WorkerThread() {
            try {
                setPriority( Thread.currentThread().getPriority() - 1);
            }
            catch (Exception e) {
            }
            try {
                setDaemon(true);
            }
            catch (Exception e) {
            }
            start();
        }
        public void run() {
            while (true) {
                try {
                    Runnable task = taskQueue.take();
                    task.run();
                }
                catch (InterruptedException e) {
                }
            }
        }
    }


}
