Will detached NSThreads always complete prior to application exit?

Question

When using NSThread's detachNewThreadSelector:toTarget:withObject:, I'm finding that the thread will fully complete its execution before the application is terminated normally if the user were to attempt to quit the application while the background process was executing.

In this case, this is the behavior I desire, but I couldn't find anything in Apple's docs that suggests that this will always be the case. The only relevant information I was able to find was the following, from Apple's Threading Programming Guide:

Important: At application exit time, detached threads can be terminated immediately but joinable threads cannot. Each joinable thread must be joined before the process is allowed to exit. Joinable threads may therefore be preferable in cases where the thread is doing critical work that should not be interrupted, such as saving data to disk.

So from this, I know that detached threads can be terminated at the time of application exit, but will they ever be terminated automatically? Or, am I always safe to assume the thread will complete its execution before the application quits?

Answer 1

You cannot assume that any thread -- including the main thread -- will ever complete execution normally, regardless of the documentation.

This is because the user can quit an application at any time, the system may lose power/panic, or the app may crash.

As for detached threads, it would not be unheard of for the system frameworks to automatically terminate the app forcibly after some timeout once the main event loop has given up the ghost.