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package cache
import (
"container/heap"
"time"
)
type expirationManager[K comparable] struct {
queue expirationQueue[K]
mapping map[K]*expirationKey[K]
}
func newExpirationManager[K comparable]() *expirationManager[K] {
q := make(expirationQueue[K], 0)
heap.Init(&q)
return &expirationManager[K]{
queue: q,
mapping: make(map[K]*expirationKey[K]),
}
}
func (m *expirationManager[K]) update(key K, expiration time.Time) {
if e, ok := m.mapping[key]; ok {
e.expiration = expiration
heap.Fix(&m.queue, e.index)
} else {
v := &expirationKey[K]{
key: key,
expiration: expiration,
}
heap.Push(&m.queue, v)
m.mapping[key] = v
}
}
func (m *expirationManager[K]) len() int {
return m.queue.Len()
}
func (m *expirationManager[K]) pop() K {
v := heap.Pop(&m.queue)
key := v.(*expirationKey[K]).key
delete(m.mapping, key)
return key
}
func (m *expirationManager[K]) remove(key K) {
if e, ok := m.mapping[key]; ok {
heap.Remove(&m.queue, e.index)
delete(m.mapping, key)
}
}
type expirationKey[K comparable] struct {
key K
expiration time.Time
index int
}
// expirationQueue implements heap.Interface and holds CacheItems.
type expirationQueue[K comparable] []*expirationKey[K]
var _ heap.Interface = (*expirationQueue[int])(nil)
func (pq expirationQueue[K]) Len() int { return len(pq) }
func (pq expirationQueue[K]) Less(i, j int) bool {
// We want Pop to give us the least based on expiration time, not the greater
return pq[i].expiration.Before(pq[j].expiration)
}
func (pq expirationQueue[K]) Swap(i, j int) {
pq[i], pq[j] = pq[j], pq[i]
pq[i].index = i
pq[j].index = j
}
func (pq *expirationQueue[K]) Push(x interface{}) {
n := len(*pq)
item := x.(*expirationKey[K])
item.index = n
*pq = append(*pq, item)
}
func (pq *expirationQueue[K]) Pop() interface{} {
old := *pq
n := len(old)
item := old[n-1]
item.index = -1 // For safety
*pq = old[0 : n-1]
return item
}
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