How can I tell reliably if a boost thread has exited its run method?

Question

I assumed joinable would indicate this, however, it does not seem to be the case.

In a worker class, I was trying to indicate that it was still processing through a predicate:

bool isRunning(){return thread_->joinable();}

Wouldn't a thread that has exited not be joinable? What am I missing... what is the meaning of boost thread::joinable?

Answer 1

You fundamentally can't do this. The reason is that the two possible answers are "Yes" and "Not when I last looked but perhaps now". There is no reliable way to determine that a thread is still inside its run method, even if there was a reliable way to determine the opposite.

Answer 2

Use thread::timed_join() with a minimal timeout. It will return false if the thread is still running.

Answer 3

Since you can join a thread even after it has terminated, joinable() will still return true until you call join() or detach(). If you want to know if a thread is still running, you should be able to call timed_join with a wait time of 0. Note that this can result in a race condition since the thread may terminate right after the call.