type timeBudget interface {
	takeAvailable() time.Duration
	returnUnused(unused time.Duration)
}

type timeBudgetImpl struct {
	sync.Mutex
	clock     clock.Clock
	budget    time.Duration
	maxBudget time.Duration
	refresh   time.Duration
	// last store last access time
	last time.Time
}

func newTimeBudget() timeBudget {
	result := &timeBudgetImpl{

	watcherIdx int
	watchers   indexedWatchers

	// Defines a time budget that can be spend on waiting for not-ready watchers
	// while dispatching event before shutting them down.
	dispatchTimeoutBudget timeBudget

	// Handling graceful termination.
	stopLock sync.RWMutex
	stopped  bool
	stopCh   chan struct{}
	stopWg   sync.WaitGroup

	clock clock.Clock

	//    happening in the test at all
	// 3) if the test was cpu-starved and we weren't able to consume events
	//    from w2 ResultCh it could have happened that its buffer was also
	//    filling in and given we no longer had timeBudget (consumed in (1))
	//    trying to put next item was simply breaking the watch
	// Using fakeTimeBudget gives us always a budget to wait and have a test
	// pick up something from ResultCh in the meantime.