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/*
* SPDX-FileCopyrightText: © Hypermode Inc. <hello@hypermode.com>
* SPDX-License-Identifier: Apache-2.0
*/
package ristretto
import (
"sync"
"time"
)
var (
// TODO: find the optimal value or make it configurable.
bucketDurationSecs = int64(5)
)
func storageBucket(t time.Time) int64 {
return (t.Unix() / bucketDurationSecs) + 1
}
func cleanupBucket(t time.Time) int64 {
// The bucket to cleanup is always behind the storage bucket by one so that
// no elements in that bucket (which might not have expired yet) are deleted.
return storageBucket(t) - 1
}
// bucket type is a map of key to conflict.
type bucket map[uint64]uint64
// expirationMap is a map of bucket number to the corresponding bucket.
type expirationMap[V any] struct {
sync.RWMutex
buckets map[int64]bucket
lastCleanedBucketNum int64
}
func newExpirationMap[V any]() *expirationMap[V] {
return &expirationMap[V]{
buckets: make(map[int64]bucket),
lastCleanedBucketNum: cleanupBucket(time.Now()),
}
}
func (m *expirationMap[_]) add(key, conflict uint64, expiration time.Time) {
if m == nil {
return
}
// Items that don't expire don't need to be in the expiration map.
if expiration.IsZero() {
return
}
bucketNum := storageBucket(expiration)
m.Lock()
defer m.Unlock()
b, ok := m.buckets[bucketNum]
if !ok {
b = make(bucket)
m.buckets[bucketNum] = b
}
b[key] = conflict
}
func (m *expirationMap[_]) update(key, conflict uint64, oldExpTime, newExpTime time.Time) {
if m == nil {
return
}
m.Lock()
defer m.Unlock()
oldBucketNum := storageBucket(oldExpTime)
oldBucket, ok := m.buckets[oldBucketNum]
if ok {
delete(oldBucket, key)
}
// Items that don't expire don't need to be in the expiration map.
if newExpTime.IsZero() {
return
}
newBucketNum := storageBucket(newExpTime)
newBucket, ok := m.buckets[newBucketNum]
if !ok {
newBucket = make(bucket)
m.buckets[newBucketNum] = newBucket
}
newBucket[key] = conflict
}
func (m *expirationMap[_]) del(key uint64, expiration time.Time) {
if m == nil {
return
}
bucketNum := storageBucket(expiration)
m.Lock()
defer m.Unlock()
_, ok := m.buckets[bucketNum]
if !ok {
return
}
delete(m.buckets[bucketNum], key)
}
// cleanup removes all the items in the bucket that was just completed. It deletes
// those items from the store, and calls the onEvict function on those items.
// This function is meant to be called periodically.
func (m *expirationMap[V]) cleanup(store store[V], policy *defaultPolicy[V], onEvict func(item *Item[V])) int {
if m == nil {
return 0
}
m.Lock()
now := time.Now()
currentBucketNum := cleanupBucket(now)
// Clean up all buckets up to and including currentBucketNum, starting from
// (but not including) the last one that was cleaned up
var buckets []bucket
for bucketNum := m.lastCleanedBucketNum + 1; bucketNum <= currentBucketNum; bucketNum++ {
// With an empty bucket, we don't need to add it to the Clean list
if b := m.buckets[bucketNum]; b != nil {
buckets = append(buckets, b)
}
delete(m.buckets, bucketNum)
}
m.lastCleanedBucketNum = currentBucketNum
m.Unlock()
for _, keys := range buckets {
for key, conflict := range keys {
expr := store.Expiration(key)
// Sanity check. Verify that the store agrees that this key is expired.
if expr.After(now) {
continue
}
cost := policy.Cost(key)
policy.Del(key)
_, value := store.Del(key, conflict)
if onEvict != nil {
onEvict(&Item[V]{Key: key,
Conflict: conflict,
Value: value,
Cost: cost,
Expiration: expr,
})
}
}
}
cleanedBucketsCount := len(buckets)
return cleanedBucketsCount
}
// clear clears the expirationMap, the caller is responsible for properly
// evicting the referenced items
func (m *expirationMap[V]) clear() {
if m == nil {
return
}
m.Lock()
m.buckets = make(map[int64]bucket)
m.lastCleanedBucketNum = cleanupBucket(time.Now())
m.Unlock()
}
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