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lru.go
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lru.go
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// Package simplelru provices a non thread-safe LRU cache with maximum size
// and TTL
package simplelru
import (
"container/list"
"time"
"darvaza.org/core"
)
// LRU Implements a least-recently-used cache with a maximum size and
// optional expiration date
type LRU[K comparable, T any] struct {
maxSize int
size int
count int
items map[K]*list.Element
eviction *list.List
onAdd func(K, T, int, time.Time)
onEvict func(K, T, int)
}
// NewLRU creates a new LRU with maximum size and eviction callback
func NewLRU[K comparable, T any](size int,
onAdd func(K, T, int, time.Time),
onEvict func(K, T, int)) *LRU[K, T] {
//
lru := &LRU[K, T]{
maxSize: size,
items: make(map[K]*list.Element),
eviction: list.New(),
onAdd: onAdd,
onEvict: onEvict,
}
return lru
}
// Len returns the number of entries in the cache
func (m *LRU[K, T]) Len() int {
return m.count
}
// Size returns the added size of all entries in the cache
func (m *LRU[K, T]) Size() int {
return m.size
}
// Available tells how much space is available without evictions
func (m *LRU[K, T]) Available() int {
return m.maxSize - m.size
}
func (m *LRU[K, T]) needsPruning() bool {
return m.size > m.maxSize
}
// Add adds an entry of a given size and optional expiration date, and
// returns true if entries were removed
func (m *LRU[K, T]) Add(key K, value T, size int, expire time.Time) bool {
var ex *time.Time
if !expire.IsZero() {
ex = &expire
}
e := entry[K, T]{
key: key,
value: value,
size: size,
expire: ex,
}
if le, ok := m.items[key]; ok {
// update entry
m.eviction.MoveToBack(le)
// old
p := le.Value.(*entry[K, T])
m.size -= p.size
// new
*p = e
m.size += e.size
} else {
// new entry
le := m.eviction.PushBack(&e)
m.items[key] = le
m.size += e.size
m.count++
}
// evict entries if needed
evicted := m.prune()
if m.onAdd != nil {
// notify the user
m.onAdd(key, value, size, expire)
}
return evicted
}
// Evict removes an entry if present
func (m *LRU[K, T]) Evict(key K) {
if le, ok := m.items[key]; ok {
m.evictElement(le)
}
}
// Get tries to find an entry, and returns its value, expiration date,
// and if it was found
func (m *LRU[K, T]) Get(key K) (T, time.Time, bool) {
var zero T
if le, ok := m.items[key]; ok {
p := le.Value.(*entry[K, T])
if !p.Expired() {
var e time.Time
m.eviction.MoveToBack(le)
if ex := p.expire; ex != nil {
e = *ex
}
return p.value, e, true
}
m.evictElement(le)
}
return zero, time.Time{}, false
}
// prune removes entries if space is needed. It tries
// the oldests expired first, and then just the oldests.
func (m *LRU[K, T]) prune() bool {
evicted := false
if m.needsPruning() {
// evict expired first
core.ListForEachElement(m.eviction,
func(le *list.Element) bool {
p := le.Value.(*entry[K, T])
if p.Expired() {
evicted = true
m.evictElement(le)
}
return !m.needsPruning()
})
}
if m.needsPruning() {
// evict oldest
core.ListForEachElement(m.eviction,
func(le *list.Element) bool {
evicted = true
m.evictElement(le)
return !m.needsPruning()
})
}
return evicted
}
// EvictExpired scans the whole cache and evicts all expired entries
func (m *LRU[K, T]) EvictExpired() bool {
var evicted bool
core.ListForEachElement(m.eviction,
func(le *list.Element) bool {
p := le.Value.(*entry[K, T])
if p.Expired() {
evicted = true
m.evictElement(le)
}
return false
})
return evicted
}
func (m *LRU[K, T]) evictElement(le *list.Element) {
p := le.Value.(*entry[K, T])
// remove from eviction list
m.eviction.Remove(le)
// remove from items
delete(m.items, p.key)
// remove from size
m.size -= p.size
// remove from count
m.count--
// notify user
if fn := m.onEvict; fn != nil {
fn(p.key, p.value, p.size)
}
}
// ForEach allows you to iterate over all non-expired entries in the Cache.
// ForEach will automatically evict any expired entry it finds along the way,
// and it will stop if the callback returns true.
func (m *LRU[K, T]) ForEach(fn func(K, T, int, time.Time) bool) {
if fn != nil {
core.ListForEachElement(m.eviction, func(le *list.Element) bool {
return m.forEachIter(le, fn)
})
}
}
func (m *LRU[K, T]) forEachIter(le *list.Element, fn func(K, T, int, time.Time) bool) bool {
var ex time.Time
p := le.Value.(*entry[K, T])
if p.Expired() {
m.evictElement(le)
return false
}
if p.expire != nil {
ex = *p.expire
}
return fn(p.key, p.value, p.size, ex)
}
type entry[K comparable, T any] struct {
key K
value T
size int
expire *time.Time
}
func (e *entry[K, T]) Expired() bool {
if e.expire == nil {
return false
}
return time.Now().After(*e.expire)
}