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// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: MPL-2.0
package simplelru
import (
"errors"
"github.com/hashicorp/golang-lru/v2/internal"
)
// EvictCallback is used to get a callback when a cache entry is evicted
type EvictCallback[K comparable, V any] func(key K, value V)
// LRU implements a non-thread safe fixed size LRU cache
type LRU[K comparable, V any] struct {
size int
evictList *internal.LruList[K, V]
items map[K]*internal.Entry[K, V]
onEvict EvictCallback[K, V]
}
// NewLRU constructs an LRU of the given size
func NewLRU[K comparable, V any](size int, onEvict EvictCallback[K, V]) (*LRU[K, V], error) {
if size <= 0 {
return nil, errors.New("must provide a positive size")
}
c := &LRU[K, V]{
size: size,
evictList: internal.NewList[K, V](),
items: make(map[K]*internal.Entry[K, V]),
onEvict: onEvict,
}
return c, nil
}
// Purge is used to completely clear the cache.
func (c *LRU[K, V]) Purge() {
for k, v := range c.items {
if c.onEvict != nil {
c.onEvict(k, v.Value)
}
delete(c.items, k)
}
c.evictList.Init()
}
// Add adds a value to the cache. Returns true if an eviction occurred.
func (c *LRU[K, V]) Add(key K, value V) (evicted bool) {
// Check for existing item
if ent, ok := c.items[key]; ok {
c.evictList.MoveToFront(ent)
ent.Value = value
return false
}
// Add new item
ent := c.evictList.PushFront(key, value)
c.items[key] = ent
evict := c.evictList.Length() > c.size
// Verify size not exceeded
if evict {
c.removeOldest()
}
return evict
}
// Get looks up a key's value from the cache.
func (c *LRU[K, V]) Get(key K) (value V, ok bool) {
if ent, ok := c.items[key]; ok {
c.evictList.MoveToFront(ent)
return ent.Value, true
}
return
}
// Contains checks if a key is in the cache, without updating the recent-ness
// or deleting it for being stale.
func (c *LRU[K, V]) Contains(key K) (ok bool) {
_, ok = c.items[key]
return ok
}
// Peek returns the key value (or undefined if not found) without updating
// the "recently used"-ness of the key.
func (c *LRU[K, V]) Peek(key K) (value V, ok bool) {
var ent *internal.Entry[K, V]
if ent, ok = c.items[key]; ok {
return ent.Value, true
}
return
}
// Remove removes the provided key from the cache, returning if the
// key was contained.
func (c *LRU[K, V]) Remove(key K) (present bool) {
if ent, ok := c.items[key]; ok {
c.removeElement(ent)
return true
}
return false
}
// RemoveOldest removes the oldest item from the cache.
func (c *LRU[K, V]) RemoveOldest() (key K, value V, ok bool) {
if ent := c.evictList.Back(); ent != nil {
c.removeElement(ent)
return ent.Key, ent.Value, true
}
return
}
// GetOldest returns the oldest entry
func (c *LRU[K, V]) GetOldest() (key K, value V, ok bool) {
if ent := c.evictList.Back(); ent != nil {
return ent.Key, ent.Value, true
}
return
}
// Keys returns a slice of the keys in the cache, from oldest to newest.
func (c *LRU[K, V]) Keys() []K {
keys := make([]K, c.evictList.Length())
i := 0
for ent := c.evictList.Back(); ent != nil; ent = ent.PrevEntry() {
keys[i] = ent.Key
i++
}
return keys
}
// Values returns a slice of the values in the cache, from oldest to newest.
func (c *LRU[K, V]) Values() []V {
values := make([]V, len(c.items))
i := 0
for ent := c.evictList.Back(); ent != nil; ent = ent.PrevEntry() {
values[i] = ent.Value
i++
}
return values
}
// Len returns the number of items in the cache.
func (c *LRU[K, V]) Len() int {
return c.evictList.Length()
}
// Resize changes the cache size.
func (c *LRU[K, V]) Resize(size int) (evicted int) {
diff := c.Len() - size
if diff < 0 {
diff = 0
}
for i := 0; i < diff; i++ {
c.removeOldest()
}
c.size = size
return diff
}
// removeOldest removes the oldest item from the cache.
func (c *LRU[K, V]) removeOldest() {
if ent := c.evictList.Back(); ent != nil {
c.removeElement(ent)
}
}
// removeElement is used to remove a given list element from the cache
func (c *LRU[K, V]) removeElement(e *internal.Entry[K, V]) {
c.evictList.Remove(e)
delete(c.items, e.Key)
if c.onEvict != nil {
c.onEvict(e.Key, e.Value)
}
}
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