// Copyright (c) 2012, Suryandaru Triandana <syndtr@gmail.com>
// All rights reserved.
//
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
package cache
import (
"sync"
"sync/atomic"
)
// lruCache represent a LRU cache state.
type lruCache struct {
sync.Mutex
recent lruNode
table map[uint64]*lruNs
capacity int
size int
}
// NewLRUCache creates a new initialized LRU cache with the given capacity.
func NewLRUCache(capacity int) Cache {
c := &lruCache{
table: make(map[uint64]*lruNs),
capacity: capacity,
}
c.recent.rNext = &c.recent
c.recent.rPrev = &c.recent
return c
}
// SetCapacity set cache capacity.
func (c *lruCache) SetCapacity(capacity int) {
c.Lock()
c.capacity = capacity
c.evict()
c.Unlock()
}
// GetNamespace return namespace object for given id.
func (c *lruCache) GetNamespace(id uint64) Namespace {
c.Lock()
defer c.Unlock()
if p, ok := c.table[id]; ok {
return p
}
p := &lruNs{
lru: c,
id: id,
table: make(map[uint64]*lruNode),
}
c.table[id] = p
return p
}
// Purge purge entire cache.
func (c *lruCache) Purge(fin PurgeFin) {
c.Lock()
for _, ns := range c.table {
ns.purgeNB(fin)
}
c.Unlock()
}
func (c *lruCache) Zap(closed bool) {
c.Lock()
for _, ns := range c.table {
ns.zapNB(closed)
}
c.table = make(map[uint64]*lruNs)
c.Unlock()
}
func (c *lruCache) evict() {
top := &c.recent
for n := c.recent.rPrev; c.size > c.capacity && n != top; {
n.state = nodeEvicted
n.rRemove()
n.evictNB()
c.size -= n.charge
n = c.recent.rPrev
}
}
type lruNs struct {
lru *lruCache
id uint64
table map[uint64]*lruNode
state nsState
}
func (ns *lruNs) Get(key uint64, setf SetFunc) (o Object, ok bool) {
lru := ns.lru
lru.Lock()
switch ns.state {
case nsZapped:
lru.Unlock()
if setf == nil {
return
}
var value interface{}
var fin func()
ok, value, _, fin = setf()
if ok {
o = &fakeObject{
value: value,
fin: fin,
}
}
return
case nsClosed:
lru.Unlock()
return
}
n, ok := ns.table[key]
if ok {
switch n.state {
case nodeEvicted:
// Insert to recent list.
n.state = nodeEffective
n.ref++
lru.size += n.charge
lru.evict()
fallthrough
case nodeEffective:
// Bump to front
n.rRemove()
n.rInsert(&lru.recent)
}
n.ref++
} else {
if setf == nil {
lru.Unlock()
return
}
var value interface{}
var charge int
var fin func()
ok, value, charge, fin = setf()
if !ok {
lru.Unlock()
return
}
n = &lruNode{
ns: ns,
key: key,
value: value,
charge: charge,
setfin: fin,
ref: 2,
}
ns.table[key] = n
n.rInsert(&lru.recent)
lru.size += charge
lru.evict()
}
lru.Unlock()
o = &lruObject{node: n}
return
}
func (ns *lruNs) Delete(key uint64, fin DelFin) bool {
lru := ns.lru
lru.Lock()
if ns.state != nsEffective {
lru.Unlock()
if fin != nil {
fin(false)
}
return false
}
n, ok := ns.table[key]
if !ok {
lru.Unlock()
if fin != nil {
fin(false)
}
return false
}
n.delfin = fin
switch n.state {
case nodeRemoved:
lru.Unlock()
return false
case nodeEffective:
lru.size -= n.charge
n.rRemove()
n.evictNB()
}
n.state = nodeRemoved
lru.Unlock()
return true
}
func (ns *lruNs) purgeNB(fin PurgeFin) {
lru := ns.lru
if ns.state != nsEffective {
return
}
for _, n := range ns.table {
n.purgefin = fin
if n.state == nodeEffective {
lru.size -= n.charge
n.rRemove()
n.evictNB()
}
n.state = nodeRemoved
}
}
func (ns *lruNs) Purge(fin PurgeFin) {
ns.lru.Lock()
ns.purgeNB(fin)
ns.lru.Unlock()
}
func (ns *lruNs) zapNB(closed bool) {
lru := ns.lru
if ns.state != nsEffective {
return
}
if closed {
ns.state = nsClosed
} else {
ns.state = nsZapped
}
for _, n := range ns.table {
if n.state == nodeEffective {
lru.size -= n.charge
n.rRemove()
}
n.state = nodeRemoved
n.execFin()
}
ns.table = nil
}
func (ns *lruNs) Zap(closed bool) {
ns.lru.Lock()
ns.zapNB(closed)
delete(ns.lru.table, ns.id)
ns.lru.Unlock()
}
type lruNode struct {
ns *lruNs
rNext, rPrev *lruNode
key uint64
value interface{}
charge int
ref int
state nodeState
setfin SetFin
delfin DelFin
purgefin PurgeFin
}
func (n *lruNode) rInsert(at *lruNode) {
x := at.rNext
at.rNext = n
n.rPrev = at
n.rNext = x
x.rPrev = n
}
func (n *lruNode) rRemove() bool {
// only remove if not already removed
if n.rPrev == nil {
return false
}
n.rPrev.rNext = n.rNext
n.rNext.rPrev = n.rPrev
n.rPrev = nil
n.rNext = nil
return true
}
func (n *lruNode) execFin() {
if n.setfin != nil {
n.setfin()
n.setfin = nil
}
if n.purgefin != nil {
n.purgefin(n.ns.id, n.key, n.delfin)
n.delfin = nil
n.purgefin = nil
} else if n.delfin != nil {
n.delfin(true)
n.delfin = nil
}
}
func (n *lruNode) evictNB() {
n.ref--
if n.ref == 0 {
if n.ns.state == nsEffective {
// remove elem
delete(n.ns.table, n.key)
// execute finalizer
n.execFin()
}
} else if n.ref < 0 {
panic("leveldb/cache: lruCache: negative node reference")
}
}
func (n *lruNode) evict() {
n.ns.lru.Lock()
n.evictNB()
n.ns.lru.Unlock()
}
type lruObject struct {
node *lruNode
once uint32
}
func (o *lruObject) Value() interface{} {
if atomic.LoadUint32(&o.once) == 0 {
return o.node.value
}
return nil
}
func (o *lruObject) Release() {
if !atomic.CompareAndSwapUint32(&o.once, 0, 1) {
return
}
o.node.evict()
o.node = nil
}