following is .m code:

#import "ThreadLabAppDelegate.h"
@interface ThreadLabAppDelegate()

- (void)processStart;
- (void)processCompleted;

@end


@implementation ThreadLabAppDelegate

@synthesize isProcessStarted;

- (void)awakeFromNib {
    //Set levelindicator's maximum value
    [levelIndicator setMaxValue:1000];
}

- (void)dealloc {
    //Never called while debugging ????
    [super dealloc];
}

- (IBAction)startProcess:(id)sender {
    //Set process flag to true
    self.isProcessStarted=YES;

    //Start Animation
    [spinIndicator startAnimation:nil];

    //perform selector in background thread
    [self performSelectorInBackground:@selector(processStart) withObject:nil];
}

- (IBAction)stopProcess:(id)sender {
    //Stop Animation
    [spinIndicator stopAnimation:nil];

    //set process flag to false
    self.isProcessStarted=NO;
}

- (void)processStart {
    int counter = 0;
    while (counter != 1000) {
        NSLog(@"Counter : %d",counter);

        //Sleep background thread to reduce CPU usage
        [NSThread sleepForTimeInterval:0.01];

        //set the level indicator value to showing progress
        [levelIndicator setIntValue:counter];

        //increment counter
        counter++;
    }

    //Notify main thread for process completed
    [self performSelectorOnMainThread:@selector(processCompleted) withObject:nil waitUntilDone:NO];

}

- (void)processCompleted {
    //Stop Animation
    [spinIndicator stopAnimation:nil];

    //set process flag to false
    self.isProcessStarted=NO;
}
@end 

I need to clear following things as per the above code.

1. How to interrupt/cancel processStart while loop from UI control?
2. I also need to show the counter value in main UI, which i suppose to do with performSelectorOnMainThread and passing argument. Just want to know, is there anyother way to do that?
3. When my app started it is showing 1 thread in Activity Monitor, but when i started the processStart() in background thread its creating two new thread,which makes the total 3 thread until or unless loop get finished.After completing the loop i can see 2 threads. So, my understanding is that, 2 thread created when i called performSelectorInBackground, but what about the thrid thread, from where it got created?
4. What if thread counts get increases on every call of selector.How to control that or my implementation is bad for such kind of requirements?

Thanks