A handle to a registered timer.

A set of timers (implemented as a priority queue).

create () is a fresh empty queue.

add t time thread adds a new event, due at time, and returns its ID. You must use Eio.Private.Fiber_context.set_cancel_fn on thread before calling pop. Your cancel function should call remove (in addition to resuming thread).

remove t key removes an event previously added with add.

pop ~now t removes and returns the earliest thread due by now. It also clears the thread's cancel function. If no thread is due yet, it returns the time the earliest thread becomes due.