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

import javax.swing.*;

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

/**
 * 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.
 * The tasks are placed into a thread-safe queue.  Several "worker" 
 * threads remove tasks from the queue and carry them out.  When
 * all the tasks have completed, the worker threads terminate.
 * The number of worker threads is specified by the user.
 * (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 MultiprocessingDemo2 extends JPanel {

    /**
     * This main routine just shows a panel of type MultiprocessingDemo2.
     */
    public static void main(String[] args) {
        JFrame window = new JFrame("Multiprocessing Demo 2");
        MultiprocessingDemo2 content = new MultiprocessingDemo2();
        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 threads that compute the image

    private ConcurrentLinkedQueue<Runnable> taskQueue;  // holds individual tasks.

    private volatile int threadsRunning; // how many threads have not yet terminated?

    private volatile boolean running;  // used to signal the thread to abort

    private JButton startButton; // button the user can click to start or abort the thread

    private JComboBox<String> threadCountSelect;  // for specifying the number of threads to be used

    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.  These threads all synchronize on the image object,
                 * although any object could be used.
                 */
                synchronized(image) {
                    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 MultiprocessingDemo2() {
        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);
        threadCountSelect = new JComboBox<String>();
        threadCountSelect.addItem("Use 1 thread.");
        threadCountSelect.addItem("Use 2 threads.");
        threadCountSelect.addItem("Use 3 threads.");
        threadCountSelect.addItem("Use 4 threads.");
        threadCountSelect.addItem("Use 5 threads.");
        threadCountSelect.addItem("Use 6 threads.");
        threadCountSelect.addItem("Use 7 threads.");
        threadCountSelect.addItem("Use 8 threads.");
        threadCountSelect.addItem("Use 9 threads.");
        threadCountSelect.addItem("Use 10 threads.");
        threadCountSelect.addItem("Use 20 threads.");
        threadCountSelect.setSelectedIndex(1);
        bottom.add(threadCountSelect);
        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 (running)
                    stop();
                else
                    start();
            }
        });
    }


    /**
     * This method is called when the user clicks the Start button,
     * while no computation is in progress.  It starts as many new
     * threads as the user has specified.  It creates one 
     * MandelbrotTask object for each row of the image and places
     * all the tasks into a queue.  The threads will remove tasks
     * from the queue to process them.  The threads are run at lower
     * priority than the event-handling thread, in order to keep the
     * GUI responsive. 
     */
    private void start() {
        startButton.setText("Abort"); // change name while computation is in progress
        threadCountSelect.setEnabled(false); // will be re-enabled when all threads finish
        int width = display.getWidth() + 2;
        int height = display.getHeight() + 2;
        if (image == null)
            image = new BufferedImage(width,height,BufferedImage.TYPE_INT_ARGB);
        Graphics g = image.getGraphics();  // fill image with gray
        g.setColor(Color.LIGHT_GRAY);
        g.fillRect(0,0,width,height);
        g.dispose();
        display.repaint();

        taskQueue = new ConcurrentLinkedQueue<Runnable>();

        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++) {
            double y = ymax - row*dy;
            MandelbrotTask task = new MandelbrotTask(row, width, maxIterations, xmin, y, dx);
            taskQueue.add(task);
        }

        int threadCount = threadCountSelect.getSelectedIndex() + 1;
        if (threadCount == 11)
            threadCount = 20;
        workers = new WorkerThread[threadCount];
        running = true;  // Set the signal before starting the threads!
        threadsRunning = threadCount;  // Records how many of the threads have not yet terminated.
        for (int i = 0; i < threadCount; i++) {
            workers[i] = new WorkerThread();
            try {
                workers[i].setPriority( Thread.currentThread().getPriority() - 1 );
            }
            catch (Exception e) {
            }
            workers[i].start();
        }
    }


    /**
     * This method is called when the user clicks the button while
     * a thread is running.  A signal is sent to the thread to terminate,
     * by setting the value of the signaling variable, running, to false.
     */
    private void stop() {
        startButton.setEnabled(false);  // will be re-enabled when all threads finish
        running = 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 threadFinished() {
        threadsRunning--;
        if (threadsRunning == 0) { // all threads have finished
            startButton.setText("Start Again");
            startButton.setEnabled(true);
            running = false; // Make sure running is false after the thread ends.
            workers = null;
            threadCountSelect.setEnabled(true); // re-enable pop-up menu
        }
    }


    /**
     * 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 and also applies the colors that it has
     * computed to the image on the screen.
     */
    private class MandelbrotTask implements Runnable {
        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.
        MandelbrotTask( int rowNumber, int width, int maxIterations, double xmin, double y, double dx) {
            this.rowNumber = rowNumber;
            this.maxIterations = maxIterations;
            this.xmin = xmin;
            this.y = y;
            this.dx = dx;
            this.width = width;
        }
        public void run() {
            int[] 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];
            }
            synchronized(image) {
                /* Add the newly computed row of pixel colors to the image.  This is
                 * synchronized because this thread and the thread that paints the
                 * display might both try to access the image simultaneously.
                 */
                image.setRGB(0,rowNumber, width, 1, rgb, 0, width);
            }
            display.repaint(0,rowNumber,width,1); // Repaint just the newly computed row.
        }
    }


    /**
     * This class defines the worker threads that carry out the tasks. 
     * A WorkerThread runs in a loop in which it retrieves a task from the 
     * taskQueue and calls the run() method in that task.  The thread 
     * terminates when the queue is empty.  (Note that for this to work 
     * properly, all the tasks must be placed into the queue before the
     * thread is started.  If the queue is empty when the thread starts,
     * the thread will simply exit immediately.)  The thread also terminates
     * if the signal variable, running, is set to false.  Just before it
     * terminates, the thread calls the threadFinished() method.
     */
    private class WorkerThread extends Thread {
        public void run() {
            try {
                while (running) {
                    Runnable task = taskQueue.poll();
                    if (task == null)
                        break;
                    task.run();
                }
            }
            finally {
                threadFinished();
            }
        }
    }


}
