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/*
* Copyright 2020 Dgraph Labs, Inc. and Contributors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
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 struct {
sync.RWMutex
buckets map[int64]bucket
}
func newExpirationMap() *expirationMap {
return &expirationMap{
buckets: make(map[int64]bucket),
}
}
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)
}
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) cleanup(store store, policy policy, onEvict onEvictFunc) {
if m == nil {
return
}
m.Lock()
now := time.Now()
bucketNum := cleanupBucket(now)
keys := m.buckets[bucketNum]
delete(m.buckets, bucketNum)
m.Unlock()
for key, conflict := range keys {
// Sanity check. Verify that the store agrees that this key is expired.
if store.Expiration(key).After(now) {
continue
}
cost := policy.Cost(key)
policy.Del(key)
_, value := store.Del(key, conflict)
if onEvict != nil {
onEvict(key, conflict, value, cost)
}
}
}
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