How to build a swing dialog for aborting a running computation thread?

[Herbert Meier]

Hello,

I've the following problem: I want to start a computation in a seperate
thread, while this computation thread is runing the application should
show a dialog to the user with a button to abort the computation. Here
is a code sample:

-------------------------------------------------------------------

// ComputationThread is ab extension of java.lang.Thread which executes

// some long lasting computation in its run() method

ComputationThread thread = new ComputationThread();


// AbortDialog is a modal JDialog which shows a JButton("Abort")
// in actionPerformed() of the ActionListener at this Button
// the computation thread will be stopped: thread.interupt

AbortDialog abortDialog = new AbortDialog(this, thread);

// run computation
thread.start();

// show abortDialog
abortDialog.setVisible(true);


try {

// wait for computation thread to has finished
thread.join();

// dispose the abort dialog
abortDialog.dispose();

// ... do things with the computation results ...

} catch (InterruptedException e) { ... }

-------------------------------------------------------------------


The abort dialog should be modal, thus no other user input in the GUI
should be possile besides pressing the abort-button. But a modal dialog
seems to be waiting till it is closed until execution will proceed,
what means that thread.join won't be reached before closing the abot
dialog. But what i want is, that the abort dialog will be cloes after
thread.join automatically.

Many thanks if anybode could post a solution for this problem.


-herbert

[d***@gmail.com]

Hi Herbert,

There are certainly many ways you could go about this. The first that
comes to mind is to implement event code such that your dialog could be
a "ComputationListener" to your thread. The next which you might find
easier would be to do something like is shown here
(http://www.javaworld.com/javaworld/jw-06-2003/jw-0606-swingworker.html)
with the SwingWorker and when your computation is complete the finished
method closes the dialog if it is still open. Hope that helps you.

Cheers,

Dan Andrews

- - - - - - - - - - - - - - - - - - - - - - - -
Ansir Development Limited www.ansir.ca
- - - - - - - - - - - - - - - - - - - - - - - -

Post by Herbert Meier
Hello,
I've the following problem: I want to start a computation in a seperate
thread, while this computation thread is runing the application should
show a dialog to the user with a button to abort the computation. Here
-------------------------------------------------------------------
// ComputationThread is ab extension of java.lang.Thread which executes
// some long lasting computation in its run() method
ComputationThread thread = new ComputationThread();
// AbortDialog is a modal JDialog which shows a JButton("Abort")
// in actionPerformed() of the ActionListener at this Button
// the computation thread will be stopped: thread.interupt
AbortDialog abortDialog = new AbortDialog(this, thread);
// run computation
thread.start();
// show abortDialog
abortDialog.setVisible(true);
try {
// wait for computation thread to has finished
thread.join();
// dispose the abort dialog
abortDialog.dispose();
// ... do things with the computation results ...
} catch (InterruptedException e) { ... }
-------------------------------------------------------------------
The abort dialog should be modal, thus no other user input in the GUI
should be possile besides pressing the abort-button. But a modal dialog
seems to be waiting till it is closed until execution will proceed,
what means that thread.join won't be reached before closing the abot
dialog. But what i want is, that the abort dialog will be cloes after
thread.join automatically.
Many thanks if anybode could post a solution for this problem.
-herbert

[Babu Kalakrishnan]

Post by Herbert Meier
Hello,
I've the following problem: I want to start a computation in a seperate
thread, while this computation thread is runing the application should
show a dialog to the user with a button to abort the computation. Here
-------------------------------------------------------------------
// ComputationThread is ab extension of java.lang.Thread which executes
// some long lasting computation in its run() method
ComputationThread thread = new ComputationThread();
// AbortDialog is a modal JDialog which shows a JButton("Abort")
// in actionPerformed() of the ActionListener at this Button
// the computation thread will be stopped: thread.interupt

Make sure that you read the API documentation of the interrupt() method
and are aware of the fact that a thread will respond to the call
immediately only when it is blocked in a specified set of methods. If
the task does not perform any of these actions (for example - a task
that involves only numeric computations), you will not get an
InterruptedException or a ClosedByInterruptException - so you would have
to explicitly check for an interrupted status periodically.

Post by Herbert Meier
AbortDialog abortDialog = new AbortDialog(this, thread);
// run computation
thread.start();
// show abortDialog
abortDialog.setVisible(true);

If the dialog is modal (as you want), anything below this line will be
executed only after the Dialog is closed - that's the reason the
approach you've taken will not work, as you've observed.

Post by Herbert Meier
try {
// wait for computation thread to has finished
thread.join();
// dispose the abort dialog
abortDialog.dispose();
// ... do things with the computation results ...
} catch (InterruptedException e) { ... }
-------------------------------------------------------------------
The abort dialog should be modal, thus no other user input in the GUI
should be possile besides pressing the abort-button. But a modal dialog
seems to be waiting till it is closed until execution will proceed,
what means that thread.join won't be reached before closing the abot
dialog. But what i want is, that the abort dialog will be cloes after
thread.join automatically.
Many thanks if anybode could post a solution for this problem.

The closing of the dialog should be initiated by the task being
performed in the thread. For this you could use a custom event that is
fired by the task when it completes, and a listener could perform the
dialog closing function.

This can still lead to certain race conditions (at least theoretically).
For instance, if your thread completes very fast, there is a very small,
but finite chance that the call to dispose the dialog can occur before
the setVisible(true) call. This is a tricky problem to avoid, and I have
seen even production code that doesn't handle this condition. What I
have done to avoid this situation is to make sure that the
thread.start() call occurs only AFTER the dialog has been made visible.
This can be accomplished by registering a WindowListener on the Dialog,
and calling thread.start() from within the windowOpened event handler.

Also it might be better to use a SwingUtilities.invokeLater wrapper to
perform the dialog closing task since it is initiated from a non-EDT
thread. (I'm not cent percent sure if the dispose() method is
thread-safe). Also this might(?) alleviate the race condition because
tasks queued through invokeLater are only processed during the next
cycle of teh EDT - but I normally use both the WindowListenerr and the
invokeLater - just to be on the safer side.

BK