This resolves #38. Read the issue for context, but after debugging the problem looks like this:

When a pty is in the uv kqueue, the poll kqueue does not properly clear the event after receiving it. The obvious fix would be to add EV_CLEAR to the event flags so that it is definitely cleared after receiving any event, however this causes a race condition in Darwin. The poll kqueue is signaled before the uv kqueue, resulting in the uv thread running once, seeing no events, and going back to sleep, while simultaneously the poll thread clears its kqueue out. This results in events being delayed until the next event comes in. You can verify that this is a race condition by adding EV_CLEAR to the original kevent call and then adding a sleep at the end of PollEvents

The code is simply waiting for data to be available for reading on the uv kqueue file descriptor, which select also does. I have migrated the Darwin-specific uv polling code to use select instead of kqueue.

I've verified that events still get processed like they should on El Capitan 10.11.3 (15D21).

Note: poll doesn't work on kqueues, otherwise I would have used that instead.