Question

In other words, if I have a process that continuously runs, but users can change parameters on the GUI that effect the process operation characteristics, where is a better place to put the process, in a NSThread or NSTimer?

Answer 1

While NSThread and NSTimer are two separate things for different needs, lets compare the two functions:

Using NSThread:

-(void) doSomethingEverySecond {
     __block int cumValue = 0; // cumulative value
     __block void(^execBlock)() = ^{        
        while (1)
        {
            @try 
            {
                // some code here that might either A: call continue to continue the loop, 
                // or B: throw an exception.
                cumValue++;
                NSLog(@"Cumulative Value is: %i", cumValue);

                if (cumValue == 5)
                    return;
            }
            @finally 
            {
                [NSThread sleepForTimeInterval:1];
            }
        }
    };

    [NSThread detachNewThreadSelector:@selector(invoke) toTarget:[execBlock copy] withObject:nil];
}

Using NSTimer:

-(void) doSomethingEverySecond {
    __block NSTimer *timer = nil;
    __block int cumValue = 0;
    __block void (^execBlock)() = ^{
        cumValue++;
        NSLog(@"Cumulative Value is: %i", cumValue);

        if (cumValue == 5)
            [timer invalidate];
    };

    timer = [NSTimer scheduledTimerWithTimeInterval:1 target:[execBlock copy] selector:@selector(invoke) userInfo:nil repeats:YES];
}

Now, if we want to something only once, NSThread is the way to go, as shown in the following:

-(void) doSomethingOnce {    
    __block void (^execBlock)() = ^{
        NSLog(@"Doing something that could take a LONG time!");
    };

    [NSThread detachNewThreadSelector:@selector(invoke) toTarget:[execBlock copy] withObject:nil];
}

Now, for the NSTimer variant:

-(void) doSomethingOnce {    
    __block void (^execBlock)() = ^{
        NSLog(@"Doing something that could take a LONG time!");
    };

    [NSTimer scheduledTimerWithTimeInterval:0 target:[execBlock copy] selector:@selector(invoke) userInfo:nil repeats:NO];
}

The reason for this is that we have complete control over the thread while using a NSThread, but if using a NSTimer, than we are executing inside a NSRunLoop which may freeze the UI if any heavy lifting is done inside. THAT is the advantage of a NSThread over a NSTimer.

You are also guaranteed that a NSThread that is detached is executed immediately, with a NSTimer, which is based on NSRunLoop, cannot, as it may or may not be able to execute immediately.

There is a 3rd alternative (well technically a fourth too, pthreads, but I will ignore that for now), GCD, but I would suggest you RTFM on that, as it’s too broad of a topic to cover in this post.