In main I spawn a new NSThread, and at a later point in main when a condition is met I want to stop the thread. How?

Question

In my main function for my command line program, I create a new instance of an NSThread subclass, and call start on it, where it runs a timer in a different thread. If the user wants to stop the timer, they type "stop" and I want it to end the thread as well.

How would I go about doing this? I'm gathering that I should call cancel on the thread, then in the main of the NSThread subclass check if isCancelled is YES, but as far as I know main is only called when I call start initially. I don't see where else I could check isCancelled in order to call [NSThread exit].

How should I handle exiting this NSThread?

Answer 1

You check for isCancelled in your NSThread subclass. You check for isCancelled throughout your code in NSThread subclass. When you call cancel, your NSThread subclass continues to run until it hits a check for isCancelled. What you do is place the isCancelled check multiple places in hopes when you call cancel it hits a isCancelled check and exits as soon as possible.

From your example code you posted I changed the TimerThread.m to look like this and it works fine:

#import "TimerThread.h"
#import "Giraffe.h"

@interface TimerThread () {
    Giraffe *giraffe;
}

@end

@implementation TimerThread

- (void)main {

    if (self.isCancelled)
        return;

    giraffe = [[Giraffe alloc] init];

    [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(calculate:) userInfo:nil repeats:YES];

    [[NSRunLoop currentRunLoop] run];
}

- (void)calculate:(NSTimer*)timer {
    if (self.isCancelled) {

        [timer invalidate];

        return;
    }

    [giraffe calculateValues:timer];
}

@end