Im a beginner to GUI and multithreading. I currently have a simulation which runs through a bug moving about in the console. I want to be able to pause the bug using a button. I have two buttons (run and pause) the run button will start the simulation and the pause button should pause it ( or make it sleep for a bit) ive managed to get the run button working but i am then unable to click pause once its running (because its in the same thread i believe) Ive read into it alot but still cant seem to work it out.. any help would be massively appreciated..
//IN MY ACTION LISTENER..
else if (E.getSource() == Pause) {
Worker pauseWorker = new Worker();
pauseWorker.execute();
IN MY NEW WORKER CLASS
import javax.swing.SwingWorker;
public class Worker extends SwingWorker<Void, Void> {
#Override
protected Void doInBackground() throws Exception {
// System.out.println("Background");
for (int i = 0; i <= 1; i++) {
Thread.sleep(1000);
System.out.println("Background running");
}
return null;
}
}
else if (E.getSource() == Pause) {
Worker pauseWorker = new Worker();
pauseWorker.execute();
This starts a new worker, does not stop the running one.
Instead, you can keep a reference to the background worker and cancel() it when the pause button is pressed. See SwingWorker.cancel()
else if (E.getSource() == Pause) {
worker.cancel(true);
}
And in the worker class, regularly check if you've been cancelled:
#Override
protected Void doInBackground() throws Exception {
// System.out.println("Background");
while(!isCancelled()) {
try {
Thread.sleep(1000);
} catch (InterruptedException ex) {
System.out.println("Background interrupted");
}
System.out.println("Background running");
}
return null;
}
If you really do need to pause rather than cancel the worker, you'll have to write your own pause() method and do the administration yourself.
To give you some idea, something like this goes into the worker class then:
boolean paused = false;
public void pause() {
paused = true;
}
public synchronized void resume() {
paused = false;
this.notify();
}
#Override
protected Void doInBackground() throws Exception {
while(!isCancelled()) {
if( paused ) {
System.out.println("Background paused, waiting for resume");
try {
synchronized(this){
wait(1000);
}
} catch (InterruptedException ex) {
System.out.println("Background interrupted");
}
} else {
System.out.println("Background running");
// do a chunk of actual work
}
}
return null;
}
Related
I am unclear on how to use wait() and notify() to pause a thread. I read talk about synchronizing, but I'm unsure how to do it in my instance. I have a music player with a progress bar where I want to pause the thread in control of syncing the progress bar with the music. Here is the thread I want to pause:
#FXML private void clickedButton(ActionEvent event){
shuffle.setOnAction(e -> {
artistPane.setText(model.getCurrentSong());
if(firstTime){
//Multithreading with JavaFX. Essentially this other thread will check the slider to make sure its on track.
sliderThread = new Task<Void>() {
#Override
protected Void call() throws Exception {
boolean fxApplicationThread = Platform.isFxApplicationThread();
System.out.println("Is call on FXApplicationThread: " + fxApplicationThread);
//this is an infinite loop because now I only need to make this thread once, pausing and starting it, as opposed to making many threads
for(;;){
Thread.sleep(100);
progressBar.setValue(controller.getPercentageDone());
}
}
};
new Thread(sliderThread).start();
firstTime = false;
}else if(!model.getIsPlaying()){
//I want to start the thread here
}
controller.shuffle(); //this will start the music on the next song
});
Here is the second half where I also want to pause and start the thread:
play.setOnAction(e -> {
controller.play(); //this will pause/start the music
if(!model.getIsPlaying()){
//where I want to pause the thread.
}else{
//I want to start the thread here
}
});
I will try to give you simple example and you try to apply it to your program...
public class TestClass extends JPanel {
/**
*
*/
private static final long serialVersionUID = 1L;
private Thread playThread ;
TestClass() {
playThread = new Thread(new Runnable() {
#Override
public void run() {
System.out.println("DO SOME THING HERE");
System.out.println("SONG WILL PLAY.....");
}
});
}
public void startMyPlayer() {
System.out.println("PLAYING NOW...");
playThread.start();
}
public void pauseMyPlayer() throws InterruptedException {
System.out.println("PAUSED NOW...");
playThread.wait();
}
public void resumeMyPlayer() {
System.out.println("RESUMING NOW...");
playThread.notify();
}
}
That's it.I hope this help you.
I'm in need of a requirement which is like as follows.
I have a jsp contains enable and disable radio buttons.
if i click on enable, a process should execute with an interval of time like for each and every 2 or 3 hours.
if disable is clicked and submitted, the
current executing task should pause until and unless again the enable
is submitted/clicked from the jsp(if enabled the above step should
continue to execute).
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
//first time execution
if(request.getParameter("lic").equals("enable") && counter==0)
{
t1.start();
counter++;
System.out.println(counter);
}
//if already started and clicks re-enable
else if(request.getParameter("lic").equals("enable") && counter>0)
{
System.out.println("thread already started");
t1.interrupt();
}
//for long pausing of thread
else if(request.getParameter("lic").equals("disable"))
{
System.out.println("thread is going to pause");
try
{
Thread.sleep(20000);
System.out.println("slept for 20 seconds");
}
catch (InterruptedException e)
{
// TODO Auto-generated catch block
System.out.println("interrupted while sleeping");
}
}
}
static int counter = 0;
static Thread t1 = new Thread()
{
public void run()
{
System.out.println("hi thread is executed");
}
};
}
I am using a thread to draw images onto a JFrame.
I added a keyListener to listen for the key P, when it is pressed, the drawing of images stops and when I press P again, the drawing should resume.
I tried using wait/ notify along with synchronized block for implementing this.
However only Pausing works, the resume never works.
Strange...
public static void main(String[] args)
{
static JFrame window1 = new JFrame();
static boolean isPaused=false;
Runnable r = new Runnable()
{
public void run()
{
while(true)
{
window1.paintImage();//fn to redraw an image
}
}
};
final Thread t = new Thread(r);
window1.addKeyListener(new KeyListener()
{
public void keyPressed(KeyEvent e)
{
if(e.getKeyCode() == KeyEvent.VK_P)
{
if(isPaused==false)
{
synchronized(t)
{
try
{
t.wait();
} catch (InterruptedException e1)
{
e1.printStackTrace();
}
}
isPaused=true;
} else
{
t.notifyAll();
isPaused=false;
}
}
}
public void keyReleased(KeyEvent arg0){}
public void keyTyped(KeyEvent arg0){}
});
t.start();
}
}
You should go through the Javadoc of Object.wait.
When t.wait() is executed, the current thread is "paused", not t.
More exactly, you are pausing the SWING Thread that is in charge of handling inputs, not the Thread t that you created to redraw the image.
t.wait() makes the SWING Thread to wait until it receive a notify() which will never come because the t.notifyAll() can only be reached by this same SWING Thread (so it is like you are going to sleep and you are waiting for yourself to wake you up... good luck with that).
Here is one solution to fix it (not the best though, since it does not care about synchronization):
final boolean [] pause = new boolean []{false};
Runnable r = new Runnable()
{
public void run()
{
while(true)
{
if(!pause[0])
window1.paintImage();//fn to redraw an image
}
}
};
...
public void keyPressed(KeyEvent e)
{
if(e.getKeyCode() == KeyEvent.VK_P)
{
if(!pause[0])
{
pause[0] = true;
} else
{
pause[0] = false;
}
}
}
I'm trying to learn Threads in Swing.
I have a Frame with a JProgressBar (progress), five JButtons (Start, Suspend, Resume, Cancel, Close), and a JLabel (label1).
The frame opens. Only Start is enabled. Start calls my class Progressor:
Updated Again Once and For All
Progressor progressor; //declared as class variable, initialized new in constructor and again in overridden done method
Here's the ButtonListener class:
public class ButtonListener implements ActionListener{
public void actionPerformed(ActionEvent e)
{
if (e.getSource() == jbStart) {
progressor.execute();
label1.setText("Progressing ...");
jbCancel.setEnabled(true);
jbResume.setEnabled(true);
jbSuspend.setEnabled(true);
jbClose.setEnabled(true);
}
if(e.getSource() == jbCancel) {
progressor.cancel(true);
label1.setText("Progress Canceled");
}
if (e.getSource() == jbSuspend) {
label1.setText(progressor.suspendProgress());
}
if (e.getSource() == jbResume) {
label1.setText(progressor.resumeProgress());
}
if (e.getSource() == jbClose) {
dispose();
}
}
}//buttonlistener
Here's the SwingWorker class:
public class Progressor extends SwingWorker<Void, Integer> {
private volatile boolean suspend = false;
private Object lock = new Object();
#Override
protected Void doInBackground() {
for (int i = 0; i <= 10; i++) {
checkForSuspend();
try {
Thread.sleep(1000);
}
catch (InterruptedException e) {
}
publish(i);
}
return null;
}
#Override
protected void process(List<Integer> list) {
int value = list.get(list.size() - 1);
progress.setValue(value);
}
public void checkForSuspend() {
synchronized (lock) {
while (suspend) {
try {
lock.wait();
} catch (InterruptedException ie){
}
}
}
}//checkForSuspend
#Override
protected void done() {
label1.setText("All Done. Press close to exit");
progressor = new Progressor();
}
public synchronized String suspendProgress() {
suspend = true;
return "Progress suspended ...";
}
public synchronized String resumeProgress() {
synchronized (lock) {
suspend = false;
lock.notify();
return "Progress resumed ...";
}
}
}//Progressor class
Everything works except the cancel doesn't doesn't actually cancel the thread (the progress bar continues).
Should I suspend it before canceling?
This How to Pause and Resume a Thread in Java from another Thread question looks very similar to yours and has some nice examples in the answers.
As for your own code and why it does not work:
You create a new progressor on every click. You should be using and controlling one, instead of creating new ones every time.
When suspending your progressor finishes work instead of suspending. As the above question states - you should be looking at the flag at some points of your computation and acting on it. Example:
while (!cancel) {
if (!suspended) {
for (int i = 1; i <= 10; i++) {
Thread.sleep(1000);
publish(i);
}
}
}
The above code will suspend when it next reaches 10 (unless you resumed it before that), and finish when you press cancel (Cancel needs to be added as an extra flag in the obvious manner).
Your thread should run inside a while loop that looks for a boolean to change value from another object, then simply change the state with setPause(true/false) when you click the button:
while(true){
if(object_everyone_can_reference.getPause()){
Thread.sleep(1000);
}
}
How exactly do i call the .interrupt() method? When I have Thread.sleep(1000), when and where do I call the .interrupt() method? is it after? What I want to do is stop Thread.sleep(1000) midway.
EDIT::
i'm having trouble stopping a thread in the middle. This is part of my code, in the StoplightThread class I have problems on the first if statement. What it is supposed to do is wait at least 10 secs then allow the user to press the button so they can change the light, if the button is pressed it should stop the running thread in this case Thread.sleep(40000). What happens is when I press the button it changes the light but does not stop the thread. If I press the button while there is still 20secs left it will add 20secs to the 10secs for the yellow light, making it yellow for 30 secs.
Edit: if you are wondering, stoplightCanvas.x == 3 is green, stoplightCanvas.x == 2 is yellow, and stoplightCanvas.x == 1 is red.
class StoplightCanvas extends Canvas implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
if (e.getSource() == cross) {
isPressed = true;
if (x == 3 && canCross)
x = 2;
}
repaint();
}
}
class StoplightThread extends Thread
{
StoplightCanvas stoplightCanvas;
StoplightThread(StoplightCanvas stoplightCanvas) {
this.stoplightCanvas = stoplightCanvas;
}
public void run()
{
if (stoplightCanvas.x == 3){
Thread.sleep(10000);
stoplightCanvas.canCross = true;
Thread.sleep(40000);
if(stoplightCanvas.isPressed)
StoplightThread.interrupt();
} else if (stoplightCanvas.x == 2) {
Thread.sleep(10000);
} else if (stoplightCanvas.x == 1) {
Thread.sleep(60000);
}
} catch (InterruptedException e){}
stoplightCanvas.toggleColor();
stoplightCanvas.repaint();
}
}
}
If you were going to call interrupt() at all, you'd call it from a different thread than the sleep().
If you want to interrupt the sleep() midway from the same thread, you can do this:
Thread.sleep( 500 );
...
Thread.sleep( 500 );
All that said, sleep() can be a code smell.
EDIT (after OP edit):
Call interrupt() on the StoplightThread from the GUI thread in your actionPerformed() method.
try this example
public class Test1 {
public static void main(String[] args) throws Exception {
Thread t = new Thread() {
public void run() {
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
t.start();
Thread.sleep(1000);
t.interrupt();
}
}
it prints
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at test.Test1$1.run(Test1.java:9)
You need a reference to the thread you want to interrupt, so that you can call interrupt() on it from a different thread.