NSRunLoop- Clarification needed

Question

I am trying to understand the concept of RunLoops. I have read Apple developer's guide on RunLoops and to some extent I have understood the concept of RunLoops. To make my concept more clearer I wrote a very simple code which uses RunLoops in it. The code can be seen below. ``` - (void)viewDidLoad { [super viewDidLoad]; thread = [[NSThread alloc] initWithTarget:self selector:@selector(testMethod) object:nil]; [thread start]; } - (void)testMethod { NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init]; NSLog(@"Thread Entered"); NSMachPort* dummyPort = [[NSMachPort alloc] init]; [[NSRunLoop currentRunLoop] addPort:dummyPort forMode:NSDefaultRunLoopMode]; while(!exitThread) { NSLog(@"Thread did some work"); [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]]; } [[NSRunLoop currentRunLoop] removePort:dummyPort forMode:NSDefaultRunLoopMode]; [dummyPort release]; NSLog(@"Thread Exited"); [pool drain]; } - (IBAction)doDomeWorkOnBackgroundThread:(i…

Accepted Answer

The change you see when you use `run` or `runUntilDate:` instead of `runMode:beforeDate:` is expected. The documentation for `runMode:beforeDate:` says this:

it returns after either the first input source is processed or `limitDate` is reached.

There is an input source responsible for handling the `performSelector:...` requests. So when you send `performSelector:...`, the run loop processes an input source and then returns.

On the other hand, the documentation for `run` says this:

it runs the receiver in the NSDefaultRunLoopMode by repeatedly invoking runMode:beforeDate:. In other words, this method effectively begins an infinite loop that processes data from the run loop’s input sources and timers.

So after the run loop processes the input source for your `performSelector:...` request, it waits for another input source to be ready. It doesn't return. Since it doesn't return, your `while` loop never gets a chance to test `exitThread`.

Your attempt to use `CFRunLoopStop` is a good idea, but unfortunately, the documentation for `run` says this:

If you want the run loop to terminate, you shouldn't use this method. Instead, use one of the other run methods and also check other arbitrary conditions of your own, in a loop.

So you can't rely on `CFRunLoopStop` to make `run` return.

Instead, you can drop to a lower level and use `CFRunLoopRun` to run the run loop, because `CFRunLoopStop` is documented to make that function return:

This function forces `rl` to stop running and return control to the function that called `CFRunLoopRun` or `CFRunLoopRunInMode` for the current run loop activation.

So try this to run your run loop:

```
while(!exitThread) {
    NSLog(@"Thread did some work");
    CFRunLoopRun([NSRunLoop currentRunLoop].getCFRunLoop);
}
```

NSRunLoop- Clarification needed

Solution

Problem