Running thread a second time

[Fleur]

If I click a button, a program is launched and a thread is started that checks if the program is active, so I can perform some tasks when the program is finished.
This seems to work okay.
However, if I click the button a second time (after the external program was closed), the thread will no longer run.
Here is my code:

    private void btnActionPerformed(java.awt.event.ActionEvent evt) {
        try {
            Runtime.getRuntime().exec( extPath + "ExtProg.exe", null, new File(extPath) );
        } catch (IOException ex) {}        
        WaitExtProgramStop();
    }

    public void WaitExtProgramStop() {
         Runnable ExtProgramStop = new Runnable () {
            public void run(){
                while(!ExtProgramStopped){
                    try {
                        System.out.println("sleeping...");
                        Thread.sleep(1000);
                    } catch (InterruptedException ex) {}
                    
                    boolean result = VBSUtils.isRunning("ExtProg.exe"); //this checkes if the program is still running
                    if (!result){
                        ExtProgramStopped = true;
                        //Do Stuff
                    }
                }
            }
         };
      Thread threadProgStop = new Thread(ExtProgramStop, "threadProgStop");
      threadProgStop.start();    
    }

Why won't the thread be run a second time?

[JosAH]

Why won't the thread be run a second time?

You can only start a thread once; if it has stopped you can't start it again. Read the API documentation for the Thread class. You have to start another (new) Thread instead; you may check if the first Thread has stopped already.

kind regards,

Jos

[Fleur]

Thanks for your answer Jos,

How does this work if I don't know how many times people will click the button that will start a new thread? I'm not supposed to use a counter to keep track on how many threads have been started so far, or am I?

[JosAH]

Thanks for your answer Jos,

How does this work if I don't know how many times people will click the button that will start a new thread? I'm not supposed to use a counter to keep track on how many threads have been started so far, or am I?

I don't know if you're up to it yet but read the API documentation for the AtomicBoolean class. Think of it as a flag you can set if it hasn't been set yet in a synchronized (atomic) way. When you want to create a thread, attempt to set this flag first. If it fails some other thread is still running, otherwise it wasn't set yet so you have now set it.

Create a new thread that does what it has to do while your original thread simply returns. When that other thread finishes it resets that flag again so new threads can be started again.

kind regards,

Jos

[masijade]

By creating the thread then and there.

Edit: Also, if you want the thread to only be started once, disable the button in the action listener.

[Fleur]

Thanks Jos,

Looks like I'm going to be busy this week-end :)

[JosAH]

Thanks Jos,

Looks like I'm going to be busy this week-end :)

Mwah, it's lousy weather, so ... also take Masijades tip in consideration: disable the button when you have started your thread and enable it again when the thread finishes (that is the responsibility of the other thread). When disabled the user simply can't start another thread.

kind regards,

Jos

[Fleur]

Okay, confused again: if the thread started and then finished, I can't start it again, you said?

[JosAH]

Okay, confused again: if the thread started and then finished, I can't start it again, you said?

Yep, that's what I said and I didn't make that up; read the API documentation for the Thread class.

kind regards,

Jos

[masijade]

:sigh: IOW you create and start a new one.

[Fleur]

okay masijade, but how can I do this? Is there a way to generate a new thread with a random name that has not been used before?

[Fubarable]

okay masijade, but how can I do this? Is there a way to generate a new thread with a random name that has not been used before?

why do you want to do this? What does a thread "name" have to do with this? I'm not even sure what a thread name is. We're discussing specific solutions here when we don't even know what the overall problem is. Perhaps your solution path is incorrect.

[JosAH]

A Thread doesn't care about its name anyway so why not synthesize a name for it?

private static int count= 0;
...
public String getName() { return "name"+count++; }
...

kind regards,

Jos

[Fleur]

@Fubarable:
The name of the thread in the example is "threadProgStop". (Wasn't that obvious?)
If I ran it once I cannot run it again, so I would need to create a new thread (with a different name), no?

The overall problem is very simple:
1. I run an externam program
2. this program generates a file
3. The external program is closed
4. my application copies that file to some other location.

Steps 1 to 4 can be accomplished multiple times one after another without my application closing.

I don't think I can accomplish this without threads: I tried, but the external application would not be able to close, it remained visible in the list of running processes (anyone know why?).

Clearly I am open to better ways to solve this issue.

@Jos: Thanks, this looks like it would do it, I should have thought of it myself :)

[Fubarable]

@Fubarable:
The name of the thread in the example is "threadProgStop". (Wasn't that obvious?)
If I ran it once I cannot run it again, so I would need to create a new thread (with a different name), no?

No. As Jos states, the name doesn't matter.

The overall problem is very simple:
1. I run an externam program
2. this program generates a file
3. The external program is closed
4. my application copies that file to some other location.

Steps 1 to 4 can be accomplished multiple times one after another without my application closing.

I don't think I can accomplish this without threads: I tried, but the external application would not be able to close, it remained visible in the list of running processes (anyone know why?).

I have had no problem with your using threads and agree that it's necessary. Shoot we all agree on this, but worrying about names and such is a bit unusual. And I'm not sure what current problems you may be having and why. I think the details and perhaps your code will be important.

[collin389]

Fleur, I think that your problem is that you cannot run:

Thread threadProgStop = new Thread(ExtProgramStop, "threadProgStop");
threadProgStop.start();

More that once because you will get an "Variable already initialized" error. I think that you can just declare: Thread threadProgStop; and the begining, and then call:

threadProgStop = new Thread(ExtProgramStop, "threadProgStop");
threadProgStop.start();

So that your program will run the Thread more than once. BTW I have no idea if this will work or not, just a thought.

[aaroncarpet]

what if he makes an object of that thread and puts it in a separate class then he can have new instances of the object

[collin389]

That is exactly what is happening when he calls new Thread()
it makes an object of class Thread. Why would he need to go through ANOTHER class to do this?

[Fleur]

Okay, I could not solve the issue with the threads. In stead I used jpoller (from sourceforge): this seems to do exactly what I need: highly recommandable