producer/consumer problem

[tim thaler]

following exercise:

5 producers baking cookies.
When at least 50 units in stock
then they inform the 2 consumers.
Consumers clear the stock.
When 100 units in stock, production stops
- use wait()/notify() concept
- use graphical output (applet/awt/swing)


okay guys,
please give me a little help

package consumer;

import javax.swing.JLabel;

public class Producer extends Thread {
	JLabel label;

	public Producer(JLabel label) {
		this.label = label;
		this.start();
	}

	public void end() {
		interrupt();
	}

	public void run() {
		while (!isInterrupted()) {
			try {
				for (int cookie = 0; cookie <= 100; cookie++) {
					label.setText(" " + cookie);
					sleep((int) (Math.random() * 80));
					if (cookie > 50) {
						synchronized (this) {
							try {
								wait((int) (Math.random() * 100 + 1));
								System.out.println("cookie-" + this.getName()
										+ " " + cookie);

							} catch (Exception e) {
								e.printStackTrace();
								System.out.println("cookie exception" + cookie);
							}
						}
					}
					if (cookie == 100) {
						end();
						label.setText("RIP");
					}
				}
				break;
			} catch (Exception e) {
			}
		}
	}
}

package consumer;

import javax.swing.JLabel;

public class Consumer extends Thread {
	JLabel label;

	public Consumer(JLabel label) {
		this.label = label;
		this.start();
	}

	public void run() {
		synchronized (this) {
			try {
				System.out.println("Producer-"+this.getName()+" started");

			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}

}

package consumer;

import java.awt.BorderLayout;

public class View2 extends JFrame {
	private JPanel contentPane;

	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					View2 frame = new View2();
					frame.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	public View2() {
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setBounds(100, 100, 600, 180);
		this.setLocationRelativeTo(null);
		setResizable(false);
		contentPane = new JPanel();
		contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
		setContentPane(contentPane);
		contentPane.setLayout(new BorderLayout(0, 0));

		JPanel panel = new JPanel();
		contentPane.add(panel, BorderLayout.NORTH);

		JLabel [] producer = new JLabel[3];
		for(int i = 0; i <3; i++){
			producer[i]  = new JLabel("Producer "+(i+1));
			producer[i].setPreferredSize(new Dimension(80, 25));
			producer[i].setBorder(new MatteBorder(1, 1, 1, 1, Color.black));
			panel.add(producer[i]);
		}

		JPanel panel_1 = new JPanel();
		contentPane.add(panel_1, BorderLayout.CENTER);

		JLabel[] cookie = new JLabel[3];
		for (int i=0; i<3; i++){
			cookie[i]= new JLabel();
			cookie[i].setPreferredSize(new Dimension(40, 25));
			cookie[i].setBorder(new MatteBorder(1, 1, 1, 1, Color.black));
			panel_1.add(cookie[i]);
			new Producer (cookie[i]);
		}

		JPanel panel_2 = new JPanel();
		contentPane.add(panel_2, BorderLayout.SOUTH);

		JLabel[] consumer = new JLabel[2];
		JLabel[] eating = new JLabel[3];
		for (int i=0; i<2; i++){
			consumer[i]= new JLabel("Consumer "+(i+1));
			consumer[i].setPreferredSize(new Dimension(80, 25));
			consumer[i].setBorder(new MatteBorder(1, 1, 1, 1, Color.black));
			panel_2.add(consumer[i]);

			eating[i] = new JLabel("hungry");
			eating[i].setPreferredSize(new Dimension(60, 25));
			eating[i].setBorder(new MatteBorder(1, 1, 1, 1,Color.black));
			panel_2.add(eating[i]);
			new Consumer(eating[i]);

		}
	}
}

[Raymond Tong]

You didn't say what your problems are
I don't think it is a good idea to start the thread itself in its constructor
Your for loop inside Producer iterate 101 times instead of 100
Your consumers should take those items from the stock?
When you have consumers clear the stock, "100 units in stock" should exclude those consumed?
Where did you use notify?

[Ranganathan Kaliyur Mannar]

You should never update Swing components other than the EDT. Use SwingUtilities.invokeLater() instead.
You can read about Swing and concurrency here

[John Vorwald]

I would add a display for the consumers, showing how many cookies they took. Also, I think I would have a display for produces and consumers showing the totals I would change the RIP to Stop or Quit. In the display to the console, you should add one to the producer number so that it matches the screen (5 instead of 4). It seems like you have the producer printing the total number of cookies after 50, but the produces should notify the consumer and the consumer should start taking cookies. This would reduce the number of cookies the producer has, except that there are 5 producers and only 2 consumers. Try this example.

[John Vorwald]

Message deleted

[John Vorwald]

Here's another attempt
1) Producers start right away, but stop when the total production reaches 100
2) Consumers start after there are 50 cookies, but stop when there are zero cookies.
3) Cntrl-C doesn't work.

Code is based on the example at
http://www.java-samples.com/showtutorial.php?tutorialid=306

public class ThreadCommicate {
    public static void main(String args[]) {
        Q q = new Q();
        final int nProducers = 5;
        for (int iProducer = 0; iProducer<nProducers; iProducer++) {
            new Producer(q, iProducer+1);
        }
        final int nConsumers = 2;
        for (int iConsumers=0; iConsumers<nConsumers; iConsumers++) {
            new Consumer(q, iConsumers+1);
        }
        System.out.println("Press Control-C to stop.");
    }
}

class Q {
    int n;
    int nProducers;
    boolean valueSet = false;
    boolean startConsuming = false;
    public Q () {
        nProducers = n = 0;
    }
    synchronized int get(int aName) throws InterruptedException {
        if(!valueSet) {
            try {
                if (nProducers>0) {
                    wait();
                }
            } catch(InterruptedException e) {
                System.out.println("InterruptedException caught");
            }
        }
        if (startConsuming) {
            if (n>0) {
                n--;
            }
        } else {
            if (n>=50) {
                System.out.printf( "Consumers can start consumming\n" );
                startConsuming = true;
            } else {
                System.out.printf( "Consumers are still wating, n = %d\n",n );
            }
        }
        int nValue = n;
        System.out.printf("Consumer %d took 1, %d remaining\n", aName, nValue);
        valueSet = false;
        notify();
        if (nValue <= 0) {
            throw new InterruptedException(String.format( "Stopping consumer %d, n = ", aName, nValue ));
        }
        return n;
    }

    synchronized void put(int aName) throws InterruptedException {
        if(valueSet) {
            try {
                wait();
            } catch(InterruptedException e) {
                System.out.printf("Woke up Producer %d\n",aName);
            }
        }
        n++;
        final int nValue = n;
        valueSet = true;
        System.out.printf("Producer %d made 1, %d remaining\n",aName, n);
        notify();
        if (n > 100) {
            nProducers--;
            throw new InterruptedException(String.format( "Stopping producer %d n = %d", aName, nValue ));
        }
    }

    public void addProducer()
    {
        this.nProducers++;
    }
}

class Producer implements Runnable {
    private Q q;
    private final int name;
    Producer(Q q, int aI) {
        q.addProducer();
        this.q = q;
        this.name = aI;
        new Thread(this, "Producer").start();
    }

    public void run() {
        try
        {
            while(true) {
                q.put(name);
            }
        } catch(InterruptedException e) {
            System.out.printf( "Finished producer %d\n", this.name );
        }
    }
}

class Consumer implements Runnable {
    private Q q;
    private final int name;
    Consumer(Q q, int aIConsumers) {
        this.q = q;
        this.name = aIConsumers;
        new Thread(this, "Consumer").start();
    }
    public void run() {
        try
        {
            boolean isFirst = true;
            while(true) {
                if (isFirst) {
                    isFirst = false;
                }
                q.get(name);
            }
        }
        catch ( InterruptedException e )
        {
            System.out.printf( "Finished consumer %d\n", this.name );
        }
    }
}

[Ranganathan Kaliyur Mannar]

Wouldn't using Lock and Condition make it easier to do this?