Destroying a Thread

[Jason Cavett]

This question is a follow-up to:
http://groups.google.com/group/comp.lang.java.programmer/browse_frm/thread/28d348f31e4d3ed7/#

I am using the BlockingQueue as suggested in my first post. It works
great (well, still not sure about a few things, but I'm trying to
figure them out). I did figure out that, if I want to stop the
thread, the best way is to return from the run method, so I have
something like this:

/**
* @see java.lang.Runnable#run()
*/
public void run() {
while (true) {
try {
File file = queue.take();

// check to see if the queue has been poisoned
if (file.equals(FileWorker.POISON_FILE)) {
break;
} else {
this.processFile(file);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}

return;
}

That way, if I close down the project, I can put a File object in the
queue that lets the thread know that it is finished (AKA, the project
has closed). (I clear the queue first so that the poison object will
be the only object left in the queue.)

The problem I am having is this - if a process is already running, I
don't really have any way of interrupting it (which I want to do if
the user is closing down the project because I don't want the very
processor intensive process running in the background while they
continue to work).

Any suggestions for stopping a process? (This would also be helpful
because I want to allow the user to choose to cancel a process that
they have already started.)


Thanks

 

[Knute Johnson]

This question is a follow-up to:
http://groups.google.com/group/comp.lang.java.programmer/browse_frm/thread/28d348f31e4d3ed7/#

I am using the BlockingQueue as suggested in my first post. It works
great (well, still not sure about a few things, but I'm trying to
figure them out). I did figure out that, if I want to stop the
thread, the best way is to return from the run method, so I have
something like this:

/**
* @see java.lang.Runnable#run()
*/
public void run() {
while (true) {
try {
File file = queue.take();

// check to see if the queue has been poisoned
if (file.equals(FileWorker.POISON_FILE)) {
break;
} else {
this.processFile(file);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}

return;
}

That way, if I close down the project, I can put a File object in the
queue that lets the thread know that it is finished (AKA, the project
has closed). (I clear the queue first so that the poison object will
be the only object left in the queue.)

The problem I am having is this - if a process is already running, I
don't really have any way of interrupting it (which I want to do if
the user is closing down the project because I don't want the very
processor intensive process running in the background while they
continue to work).

Any suggestions for stopping a process? (This would also be helpful
because I want to allow the user to choose to cancel a process that
they have already started.)


Thanks

public void run() {
try {
while (true) {
????.take();
}
} catch (InterruptedException ie) { }
}

Just interrupt the thread. take() throws an InterruptedException if it
is interrupted while waiting.

 

[Tom Hawtin]

The problem I am having is this - if a process is already running, I
don't really have any way of interrupting it (which I want to do if
the user is closing down the project because I don't want the very
processor intensive process running in the background while they
continue to work).

I suggest just checking a flag periodically.

You can use Thread.interrupt which should interrupt I/O and any waits.
However, interruptible I/O has been quietly deprecated and interrupts
are more often than not handled incorrectly. Interrupting a thread that
is loading a class can be a bad move (the class may fail to load, and
therefore becomes completely unloadable with that class loader).

Tom Hawtin

 

[Jason Cavett]

public void run() {
try {
while (true) {
????.take();
}
} catch (InterruptedException ie) { }

}

Just interrupt the thread. take() throws an InterruptedException if it
is interrupted while waiting.

--

Knute Johnson
email s/nospam/knute/- Hide quoted text -

- Show quoted text -

But what if I made it to this line...

this.processFile(file);

And now I'm doing the processing of the file (which can take quite a
long time - 10 minutes or more) and I want to interrupt that
processing? That's what I'm curious about. I already know how to
stop the thread if the queue is in waiting state.

 

[Knute Johnson]

But what if I made it to this line...

this.processFile(file);

And now I'm doing the processing of the file (which can take quite a
long time - 10 minutes or more) and I want to interrupt that
processing? That's what I'm curious about. I already know how to
stop the thread if the queue is in waiting state.

You need some sort of test or exception capture in processFile(). If
you have the source just check a flag or use the Thread.interrupted() to
test. If you don't have the source to processFile() then it may be
possible to make the run method use a daemon thread and close your
program to stop it.