Question

[NSThread detachNewThreadSelector:@selector(addressLocation:) toTarget:self withObject:parameter];

[self addressLocation:parameter];

Should these two statements do the same thing? Because one of them (the second one) gives me an accurate result, and the other consistently gives me a random location off the coast of Africa. From what I have read, they should both do the same thing; execute addressLocation with the argument ‘parameter.’ The only difference is the thread, but it is accessing a global volatile variable, so that shouldn’t matter, should it?

Answer 1

Threads are much more complicated than that. When you call detachNewThreadSelector, you are creating a new thread, but there’s no simple way for you to know when that call completes. It could complete before the next line of code in the calling thread or many seconds later.

If you create the thread first, you can then use performSelector:onThread:withObject:waitUntilDone and you should get the same result as if you used [self addressLocation:parameter]. That won’t do you a lot of good though because your main thread will be doing nothing while you wait for the result.

There are lots of ways to get data back from a thread — I like to call performSelectorOnMainThread from the secondary thread to send the data back to the main thread, for example.

I would read up on Grand Central Dispatch to see if it suits your needs.