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package mru
// Sync reconciles the order's membership to present.
//
// Surviving keys keep their relative recency order,
// absent keys are dropped,
// and newly present keys are placed before the survivors,
// since new members are presumed recently used.
func (order *Order[K]) Sync(present map[K]struct{}) {
order.mu.Lock()
defer order.mu.Unlock()
keys := order.Keys()
survivors := make(map[K]struct{}, len(present))
for _, key := range keys {
if _, ok := present[key]; ok {
survivors[key] = struct{}{}
}
}
next := make([]K, 0, len(present))
for key := range present {
if _, ok := survivors[key]; !ok {
next = append(next, key)
}
}
for _, key := range keys {
if _, ok := survivors[key]; ok {
next = append(next, key)
}
}
order.snapshot.Store(&next)
}
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