Re: thread wait

Lew <>
Mon, 13 Aug 2007 08:38:56 -0400
korcs wrote:
Patricia Shanahan wrote:

I can't work out what is going on, but one obvious problem is that it
looks as though some actions on threadsSuspended appear to be outside
the synchronized blocks.

Given the lack of a complete program, it is hard to check issues such as
whether the event handling thread gets suspended and whether the same
object is used for all synchronization that protects the same variable.

Here is an SSCCE:

import java.awt.*;
import java.awt.event.*;
import java.util.Vector;

You might find ArrayList preferable.

public class DynamicPathGenerator extends Frame implements Runnable {

It's a little unusual to launch an entire Frame (why not a JFrame?) in a
subthread of itself. In your case that is probably not the thing to do.


Don't use TAB characters in Usenet posts.

      * Member variables
     * @param clock Thread that provides the ticks for the main program
     * @param clock_period Shows how often the clock ticks
     * @param serialVersionUID Id needed for serialization
     * @param ta TextArea for system outputs
    Thread clock;
    boolean threadsSuspended = false;

Redundant initialization.

You should consider providing access specification for your instance
variables, almost always "private".

     static final int clock_period = 1000;

Compile time constants conventionally are named in all uppercase letters.
Private? Public?

Code is a little easier to read if you put all static variables together and
all non-static variables together in separate "paragraphs".

     private static final long serialVersionUID = 1L;
    TextArea ta = new TextArea("DynamicPathGenerator ver 1.0\n\n", 10,
    int counter;

     * AWT classes

     * Window closing class
    class MyWindowCloser extends WindowAdapter {

          public void windowClosing(WindowEvent e) {


          } // method windowClosing

    } // class MyWindowCloser

     * Start button listener
    class startListener implements ActionListener {

        public void actionPerformed (ActionEvent e) {

            ta.append("DynamicPathGenerator> simulation started\n");
            threadsSuspended = false;

            if(!clock.isAlive()) {


            else {

                synchronized(this) {

Remember what Thomas Hawtin said, echoing Patricia Shanahan's advice?

Note that 'this' within an inner class refers to inner instance, not the outer. Even Brian Goetz managed to publish a book with this mistake.


        } // method actionPerformed

    } // class startListener

     * Stop button listener
    class stopListener implements ActionListener {

        public void actionPerformed (ActionEvent e) {

            ta.append("DynamicPathGenerator> simulation stopped\n");

            threadsSuspended = true;

        } // method actionPerformed

    } // class stopListener

     * Constructor of the class.
    public DynamicPathGenerator() { // CONSTRUCTOR

        clock = new Thread(this);

        Button start = new Button("Simulation starten"); //Gombok
        Button stop = new Button("Simulation beenden");

        Panel p1 = new Panel(new GridLayout(2,3));
        Panel p3 = new Panel();

        // add panel elements


        // arrange panel elements

        add(p1, BorderLayout.NORTH); add(p3, BorderLayout.SOUTH);

        // adding listeners

        start.addActionListener(new startListener () );
        stop.addActionListener(new stopListener () );

        addWindowListener( new MyWindowCloser () );

    public void putText(String text) {

    public void run()

Why do you need to run a whole Frame in the subthread?

         try {

                this.putText(new Integer(counter).toString());

You ignored the advice about Integer.toString(counter), I see.

                synchronized(this) {

wait() and notify() / notifyAll() have to be called on the same monitor.

                     while (threadsSuspended)
        } // while
        } catch (InterruptedException e) {


You ignored the advice about the redundant "return", I see.

     } // method run

     * The main method
    public static void main(String argv[]) throws Exception {

Why are you throwing an Exception from main()?

         DynamicPathGenerator dpg = new DynamicPathGenerator();

      } // method main

} // class DynamicPathGenerator



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