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local_storage.go
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local_storage.go
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package glocalstorage
import (
"fmt"
"runtime"
"sync"
"time"
)
type backgroundCleaner struct {
Interval time.Duration
stop chan bool
}
type node struct {
key string
value []byte
expiration *time.Time
next *node
prev *node
}
type CacheItem struct {
Value []byte
Expiration *time.Time
}
type StorageConfig struct {
Expiration time.Duration // if set = 0 items will never expire
Capacity int64
CleanupInterval time.Duration // if set > 0 will run a background storage cleaner
}
type InternalLocalStorage struct {
kv_storage map[string]*node
head *node
tail *node
size int64
defaultConfigs StorageConfig
lock *sync.Mutex
cleaner *backgroundCleaner
}
type LocalStorage struct {
*InternalLocalStorage
}
func New(config StorageConfig) *LocalStorage {
intLocalStorage := &InternalLocalStorage{
kv_storage: make(map[string]*node),
head: nil,
tail: nil,
size: 0,
defaultConfigs: config,
lock: &sync.Mutex{},
}
localStorage := &LocalStorage{InternalLocalStorage: intLocalStorage}
cleanupInterval := config.CleanupInterval
if cleanupInterval > 0 && config.Expiration > 0 { // run background cleaner iff nodes can actually expire
runCleaner(intLocalStorage, cleanupInterval)
runtime.SetFinalizer(localStorage, stopCleaner)
} else {
fmt.Println("Background cleaner has NOT been SET")
}
return localStorage
}
func runCleaner(intLocalStorage *InternalLocalStorage, cleanupInterval time.Duration) {
cleaner := &backgroundCleaner{
Interval: cleanupInterval,
stop: make(chan bool),
}
intLocalStorage.cleaner = cleaner
go cleaner.Run(intLocalStorage)
}
func (cleaner *backgroundCleaner) Run(intLocalStorage *InternalLocalStorage) {
ticker := time.NewTicker(cleaner.Interval)
for {
select {
case <-ticker.C:
fmt.Println("STARTING Backgroung cleaner")
intLocalStorage.CleanUpExpired()
case <-cleaner.stop:
ticker.Stop()
fmt.Println("STOPPED Backgroung cleaner")
return
}
}
}
func stopCleaner(c *LocalStorage) {
fmt.Println("Stopping backgroung cleaner")
c.cleaner.stop <- true
}
func (local_storage *InternalLocalStorage) Set(key string, value []byte, itemExpiration time.Duration) (updated bool) {
local_storage.lock.Lock()
defer local_storage.lock.Unlock()
var expiration *time.Time
if itemExpiration > 0 {
tmp := time.Now().Add(itemExpiration)
expiration = &tmp
} else if itemExpiration == 0 {
expiration = nil
} else if local_storage.defaultConfigs.Expiration > 0 && itemExpiration == -1 {
tmp := time.Now().Add(local_storage.defaultConfigs.Expiration)
expiration = &tmp
} else {
expiration = nil
}
// key does not exist --> insert
if local_storage.kv_storage[key] == nil {
if local_storage.head == nil && local_storage.tail == nil { // first element
tmp_node := &node{
key: key,
value: value,
expiration: expiration, // results in the time when the value expires: if defaultExpiration = 1day and now is 24Jan --> expiration = 25Jan
next: nil,
prev: nil,
}
local_storage.head = tmp_node
local_storage.tail = local_storage.head
local_storage.kv_storage[key] = tmp_node
} else {
if local_storage.size == local_storage.defaultConfigs.Capacity {
local_storage.evict()
}
tmp_node := &node{
key: key,
value: value,
expiration: expiration, // results in the time when the value expires: if defaultExpiration = 1day and now is 24Jan --> expiration = 25Jan
next: local_storage.head,
prev: nil,
}
local_storage.head.prev = tmp_node
local_storage.head = tmp_node
local_storage.kv_storage[key] = tmp_node
}
local_storage.size++
return false
} else { // key does already exist --> update value and bring up the updated node to be the new head
// update value
newHead := local_storage.kv_storage[key]
newHead.value = value
// update head
local_storage.updateHead(newHead)
return true
}
}
func (local_storage *InternalLocalStorage) Get(key string) (cacheItem *CacheItem, hit bool) {
local_storage.lock.Lock()
defer local_storage.lock.Unlock()
newHead := local_storage.kv_storage[key]
if newHead == nil {
return nil, false
} else if local_storage.isNodeExpired(newHead) {
local_storage.removeNode(newHead)
return nil, false
}
local_storage.updateHead(newHead)
return &CacheItem{Value: newHead.value, Expiration: newHead.expiration}, true
}
func (local_storage *InternalLocalStorage) Delete(key string) bool {
local_storage.lock.Lock()
defer local_storage.lock.Unlock()
toRemove := local_storage.kv_storage[key]
if toRemove == nil {
return false
}
local_storage.removeNode(toRemove)
return true
}
func (local_storage *InternalLocalStorage) Clear() {
local_storage.lock.Lock()
defer local_storage.lock.Unlock()
for i := local_storage.tail; i != nil; {
local_storage.removeNode(i)
i = local_storage.tail
}
}
func (local_storage *InternalLocalStorage) Show() {
for i := local_storage.head; i != nil; {
fmt.Println("Key: ", i.key)
fmt.Println("Value: ", string(i.value))
fmt.Println("ttl: ", i.expiration)
i = i.next
}
}
// LRU policy eviction
func (local_storage *InternalLocalStorage) evict() {
to_evict := local_storage.tail
local_storage.tail = to_evict.prev
local_storage.tail.next = nil
local_storage.size--
to_evict.next = nil
to_evict.prev = nil
delete(local_storage.kv_storage, to_evict.key)
}
func (local_storage *InternalLocalStorage) updateHead(newHead *node) {
if local_storage.head == local_storage.tail || newHead == local_storage.head {
return
}
prev_ := newHead.prev
prev_.next = newHead.next
if prev_.next == nil {
local_storage.tail = prev_
}
newHead.next = local_storage.head
newHead.prev = nil
local_storage.head = newHead
local_storage.head.next.prev = local_storage.head
}
func (local_storage *InternalLocalStorage) CleanUpExpired() {
local_storage.lock.Lock()
defer local_storage.lock.Unlock()
for i := local_storage.head; i != nil; {
if local_storage.isNodeExpired(i) {
local_storage.removeNode(i)
}
i = i.next
}
}
func (local_storage *InternalLocalStorage) isNodeExpired(node *node) bool {
if node.expiration != nil {
return node.expiration.Before(time.Now())
}
return false
}
func (local_storage *InternalLocalStorage) removeNode(nodeToRemove *node) {
if nodeToRemove.prev == nil && nodeToRemove.next == nil { // last elem
local_storage.head = nil
local_storage.tail = nil
} else if nodeToRemove.prev == nil { // head
local_storage.head = nodeToRemove.next
local_storage.head.prev = nil
} else if nodeToRemove.next == nil { // tail
local_storage.tail = nodeToRemove.prev
local_storage.tail.next = nil
} else {
nodeToRemove.prev.next = nodeToRemove.next
nodeToRemove.next.prev = nodeToRemove.prev
}
nodeToRemove.next = nil
nodeToRemove.prev = nil
delete(local_storage.kv_storage, nodeToRemove.key)
local_storage.size--
}