The callback_handler function should be run as an infinite loop. This was previously handled by libuv:

but has not been replaced after the removal of libuv.

In the absence of such a loop, the callback_handler thread stops after a single run through the different update piles and stops listening to further changes thereafter.

I managed to fixed the issue by enclosing the part after the mutex request into a simple while (true) {... loop, but I'm not 100% certain that this would be the appropriate way of doing things since I actually have no experience whatsoever with C++ 😄 If this approach seems alright though, I'd be happy to submit this very simple PR.