type Wait interface {
	// Register waits returns a chan that waits on the given ID.
	// The chan will be triggered when Trigger is called with
	// the same ID.
	Register(id uint64) <-chan interface{}
	// Trigger triggers the waiting chans with the given ID.
	Trigger(id uint64, x interface{})
	IsRegistered(id uint64) bool
}

type WaitTime interface {
	// Wait returns a chan that waits on the given logical deadline.
	// The chan will be triggered when Trigger is called with a
	// deadline that is later than the one it is waiting for.
	Wait(deadline uint64) <-chan struct{}
	// Trigger triggers all the waiting chans with an earlier logical deadline.
	Trigger(deadline uint64)
}