how to join thread if joinable do nothing otherwise?

Question

I'm using boost::thread join method to wait until thread is finished. But if I try to join the thread when it already finished I receive an exception. So how can I:

Join thread if active and do nothing if not active?

Answer 1

Use the joinable() function to check whether it should be joined:

if (thread.joinable()) thread.join();

You can (in fact, you must) join a thread even if it's already finished, unless it's been detached. It's an error to join it twice, or to join an empty or detached thread.