// 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 provides interface and implementation of a cache algorithms.
package cache
import (
"sync"
"sync/atomic"
"unsafe"
"github.com/syndtr/goleveldb/leveldb/util"
)
// Cacher provides interface to implements a caching functionality.
// An implementation must be safe for concurrent use.
type Cacher interface {
// Capacity returns cache capacity.
Capacity() int
// SetCapacity sets cache capacity.
SetCapacity(capacity int)
// Promote promotes the 'cache node'.
Promote(n *Node)
// Ban evicts the 'cache node' and prevent subsequent 'promote'.
Ban(n *Node)
// Evict evicts the 'cache node'.
Evict(n *Node)
// EvictNS evicts 'cache node' with the given namespace.
EvictNS(ns uint64)
// EvictAll evicts all 'cache node'.
EvictAll()
// Close closes the 'cache tree'
Close() error
}
// Value is a 'cacheable object'. It may implements util.Releaser, if
// so the the Release method will be called once object is released.
type Value interface{}
// NamespaceGetter provides convenient wrapper for namespace.
type NamespaceGetter struct {
Cache *Cache
NS uint64
}
// Get simply calls Cache.Get() method.
func (g *NamespaceGetter) Get(key uint64, setFunc func() (size int, value Value)) *Handle {
return g.Cache.Get(g.NS, key, setFunc)
}
// The hash tables implementation is based on:
// "Dynamic-Sized Nonblocking Hash Tables", by Yujie Liu,
// Kunlong Zhang, and Michael Spear.
// ACM Symposium on Principles of Distributed Computing, Jul 2014.
const (
mInitialSize = 1 << 4
mOverflowThreshold = 1 << 5
mOverflowGrowThreshold = 1 << 7
)
type mBucket struct {
mu sync.Mutex
node []*Node
frozen bool
}
func (b *mBucket) freeze() []*Node {
b.mu.Lock()
defer b.mu.Unlock()
if !b.frozen {
b.frozen = true
}
return b.node
}
func (b *mBucket) get(r *Cache, h *mNode, hash uint32, ns, key uint64, noset bool) (done, added bool, n *Node) {
b.mu.Lock()
if b.frozen {
b.mu.Unlock()
return
}
// Scan the node.
for _, n := range b.node {
if n.hash == hash && n.ns == ns && n.key == key {
atomic.AddInt32(&n.ref, 1)
b.mu.Unlock()
return true, false, n
}
}
// Get only.
if noset {
b.mu.Unlock()
return true, false, nil
}
// Create node.
n = &Node{
r: r,
hash: hash,
ns: ns,
key: key,
ref: 1,
}
// Add node to bucket.
b.node = append(b.node, n)
bLen := len(b.node)
b.mu.Unlock()
// Update counter.
grow := atomic.AddInt32(&r.nodes, 1) >= h.growThreshold
if bLen > mOverflowThreshold {
grow = grow || atomic.AddInt32(&h.overflow, 1) >= mOverflowGrowThreshold
}
// Grow.
if grow && atomic.CompareAndSwapInt32(&h.resizeInProgess, 0, 1) {
nhLen := len(h.buckets) << 1
nh := &mNode{
buckets: make([]unsafe.Pointer, nhLen),
mask: uint32(nhLen) - 1,
pred: unsafe.Pointer(h),
growThreshold: int32(nhLen * mOverflowThreshold),
shrinkThreshold: int32(nhLen >> 1),
}
ok := atomic.CompareAndSwapPointer(&r.mHead, unsafe.Pointer(h), unsafe.Pointer(nh))
if !ok {
panic("BUG: failed swapping head")
}
go nh.initBuckets()
}
return true, true, n
}
func (b *mBucket) delete(r *Cache, h *mNode, hash uint32, ns, key uint64) (done, deleted bool) {
b.mu.Lock()
if b.frozen {
b.mu.Unlock()
return
}
// Scan the node.
var (
n *Node
bLen int
)
for i := range b.node {
n = b.node[i]
if n.ns == ns && n.key == key {
if atomic.LoadInt32(&n.ref) == 0 {
deleted = true
// Call releaser.
if n.value != nil {
if r, ok := n.value.(util.Releaser); ok {
r.Release()
}
n.value = nil
}
// Remove node from bucket.
b.node = append(b.node[:i], b.node[i+1:]...)
bLen = len(b.node)
}
break
}
}
b.mu.Unlock()
if deleted {
// Call OnDel.
for _, f := range n.onDel {
f()
}
// Update counter.
atomic.AddInt32(&r.size, int32(n.size)*-1)
shrink := atomic.AddInt32(&r.nodes, -1) < h.shrinkThreshold
if bLen >= mOverflowThreshold {
atomic.AddInt32(&h.overflow, -1)
}
// Shrink.
if shrink && len(h.buckets) > mInitialSize && atomic.CompareAndSwapInt32(&h.resizeInProgess, 0, 1) {
nhLen := len(h.buckets) >> 1
nh := &mNode{
buckets: make([]unsafe.Pointer, nhLen),
mask: uint32(nhLen) - 1,
pred: unsafe.Pointer(h),
growThreshold: int32(nhLen * mOverflowThreshold),
shrinkThreshold: int32(nhLen >> 1),
}
ok := atomic.CompareAndSwapPointer(&r.mHead, unsafe.Pointer(h), unsafe.Pointer(nh))
if !ok {
panic("BUG: failed swapping head")
}
go nh.initBuckets()
}
}
return true, deleted
}
type mNode struct {
buckets []unsafe.Pointer // []*mBucket
mask uint32
pred unsafe.Pointer // *mNode
resizeInProgess int32
overflow int32
growThreshold int32
shrinkThreshold int32
}
func (n *mNode) initBucket(i uint32) *mBucket {
if b := (*mBucket)(atomic.LoadPointer(&n.buckets[i])); b != nil {
return b
}
p := (*mNode)(atomic.LoadPointer(&n.pred))
if p != nil {
var node []*Node
if n.mask > p.mask {
// Grow.
pb := (*mBucket)(atomic.LoadPointer(&p.buckets[i&p.mask]))
if pb == nil {
pb = p.initBucket(i & p.mask)
}
m := pb.freeze()
// Split nodes.
for _, x := range m {
if x.hash&n.mask == i {
node = append(node, x)
}
}
} else {
// Shrink.
pb0 := (*mBucket)(atomic.LoadPointer(&p.buckets[i]))
if pb0 == nil {
pb0 = p.initBucket(i)
}
pb1 := (*mBucket)(atomic.LoadPointer(&p.buckets[i+uint32(len(n.buckets))]))
if pb1 == nil {
pb1 = p.initBucket(i + uint32(len(n.buckets)))
}
m0 := pb0.freeze()
m1 := pb1.freeze()
// Merge nodes.
node = make([]*Node, 0, len(m0)+len(m1))
node = append(node, m0...)
node = append(node, m1...)
}
b := &mBucket{node: node}
if atomic.CompareAndSwapPointer(&n.buckets[i], nil, unsafe.Pointer(b)) {
if len(node) > mOverflowThreshold {
atomic.AddInt32(&n.overflow, int32(len(node)-mOverflowThreshold))
}
return b
}
}
return (*mBucket)(atomic.LoadPointer(&n.buckets[i]))
}
func (n *mNode) initBuckets() {
for i := range n.buckets {
n.initBucket(uint32(i))
}
atomic.StorePointer(&n.pred, nil)
}
// Cache is a 'cache map'.
type Cache struct {
mu sync.RWMutex
mHead unsafe.Pointer // *mNode
nodes int32
size int32
cacher Cacher
closed bool
}
// NewCache creates a new 'cache map'. The cacher is optional and
// may be nil.
func NewCache(cacher Cacher) *Cache {
h := &mNode{
buckets: make([]unsafe.Pointer, mInitialSize),
mask: mInitialSize - 1,
growThreshold: int32(mInitialSize * mOverflowThreshold),
shrinkThreshold: 0,
}
for i := range h.buckets {
h.buckets[i] = unsafe.Pointer(&mBucket{})
}
r := &Cache{
mHead: unsafe.Pointer(h),
cacher: cacher,
}
return r
}
func (r *Cache) getBucket(hash uint32) (*mNode, *mBucket) {
h := (*mNode)(atomic.LoadPointer(&r.mHead))
i := hash & h.mask
b := (*mBucket)(atomic.LoadPointer(&h.buckets[i]))
if b == nil {
b = h.initBucket(i)
}
return h, b
}
func (r *Cache) delete(n *Node) bool {
for {
h, b := r.getBucket(n.hash)
done, deleted := b.delete(r, h, n.hash, n.ns, n.key)
if done {
return deleted
}
}
return false
}
// Nodes returns number of 'cache node' in the map.
func (r *Cache) Nodes() int {
return int(atomic.LoadInt32(&r.nodes))
}
// Size returns sums of 'cache node' size in the map.
func (r *Cache) Size() int {
return int(atomic.LoadInt32(&r.size))
}
// Capacity returns cache capacity.
func (r *Cache) Capacity() int {
if r.cacher == nil {
return 0
}
return r.cacher.Capacity()
}
// SetCapacity sets cache capacity.
func (r *Cache) SetCapacity(capacity int) {
if r.cacher != nil {
r.cacher.SetCapacity(capacity)
}
}
// Get gets 'cache node' with the given namespace and key.
// If cache node is not found and setFunc is not nil, Get will atomically creates
// the 'cache node' by calling setFunc. Otherwise Get will returns nil.
//
// The returned 'cache handle' should be released after use by calling Release
// method.
func (r *Cache) Get(ns, key uint64, setFunc func() (size int, value Value)) *Handle {
r.mu.RLock()
defer r.mu.RUnlock()
if r.closed {
return nil
}
hash := murmur32(ns, key, 0xf00)
for {
h, b := r.getBucket(hash)
done, _, n := b.get(r, h, hash, ns, key, setFunc == nil)
if done {
if n != nil {
n.mu.Lock()
if n.value == nil {
if setFunc == nil {
n.mu.Unlock()
n.unref()
return nil
}
n.size, n.value = setFunc()
if n.value == nil {
n.size = 0
n.mu.Unlock()
n.unref()
return nil
}
atomic.AddInt32(&r.size, int32(n.size))
}
n.mu.Unlock()
if r.cacher != nil {
r.cacher.Promote(n)
}
return &Handle{unsafe.Pointer(n)}
}
break
}
}
return nil
}
// Delete removes and ban 'cache node' with the given namespace and key.
// A banned 'cache node' will never inserted into the 'cache tree'. Ban
// only attributed to the particular 'cache node', so when a 'cache node'
// is recreated it will not be banned.
//
// If onDel is not nil, then it will be executed if such 'cache node'
// doesn't exist or once the 'cache node' is released.
//
// Delete return true is such 'cache node' exist.
func (r *Cache) Delete(ns, key uint64, onDel func()) bool {
r.mu.RLock()
defer r.mu.RUnlock()
if r.closed {
return false
}
hash := murmur32(ns, key, 0xf00)
for {
h, b := r.getBucket(hash)
done, _, n := b.get(r, h, hash, ns, key, true)
if done {
if n != nil {
if onDel != nil {
n.mu.Lock()
n.onDel = append(n.onDel, onDel)
n.mu.Unlock()
}
if r.cacher != nil {
r.cacher.Ban(n)
}
n.unref()
return true
}
break
}
}
if onDel != nil {
onDel()
}
return false
}
// Evict evicts 'cache node' with the given namespace and key. This will
// simply call Cacher.Evict.
//
// Evict return true is such 'cache node' exist.
func (r *Cache) Evict(ns, key uint64) bool {
r.mu.RLock()
defer r.mu.RUnlock()
if r.closed {
return false
}
hash := murmur32(ns, key, 0xf00)
for {
h, b := r.getBucket(hash)
done, _, n := b.get(r, h, hash, ns, key, true)
if done {
if n != nil {
if r.cacher != nil {
r.cacher.Evict(n)
}
n.unref()
return true
}
break
}
}
return false
}
// EvictNS evicts 'cache node' with the given namespace. This will
// simply call Cacher.EvictNS.
func (r *Cache) EvictNS(ns uint64) {
r.mu.RLock()
defer r.mu.RUnlock()
if r.closed {
return
}
if r.cacher != nil {
r.cacher.EvictNS(ns)
}
}
// EvictAll evicts all 'cache node'. This will simply call Cacher.EvictAll.
func (r *Cache) EvictAll() {
r.mu.RLock()
defer r.mu.RUnlock()
if r.closed {
return
}
if r.cacher != nil {
r.cacher.EvictAll()
}
}
// Close closes the 'cache map' and forcefully releases all 'cache node'.
func (r *Cache) Close() error {
r.mu.Lock()
if !r.closed {
r.closed = true
h := (*mNode)(r.mHead)
h.initBuckets()
for i := range h.buckets {
b := (*mBucket)(h.buckets[i])
for _, n := range b.node {
// Call releaser.
if n.value != nil {
if r, ok := n.value.(util.Releaser); ok {
r.Release()
}
n.value = nil
}
// Call OnDel.
for _, f := range n.onDel {
f()
}
n.onDel = nil
}
}
}
r.mu.Unlock()
// Avoid deadlock.
if r.cacher != nil {
if err := r.cacher.Close(); err != nil {
return err
}
}
return nil
}
// CloseWeak closes the 'cache map' and evict all 'cache node' from cacher, but
// unlike Close it doesn't forcefully releases 'cache node'.
func (r *Cache) CloseWeak() error {
r.mu.Lock()
if !r.closed {
r.closed = true
}
r.mu.Unlock()
// Avoid deadlock.
if r.cacher != nil {
r.cacher.EvictAll()
if err := r.cacher.Close(); err != nil {
return err
}
}
return nil
}
// Node is a 'cache node'.
type Node struct {
r *Cache
hash uint32
ns, key uint64
mu sync.Mutex
size int
value Value
ref int32
onDel []func()
CacheData unsafe.Pointer
}
// NS returns this 'cache node' namespace.
func (n *Node) NS() uint64 {
return n.ns
}
// Key returns this 'cache node' key.
func (n *Node) Key() uint64 {
return n.key
}
// Size returns this 'cache node' size.
func (n *Node) Size() int {
return n.size
}
// Value returns this 'cache node' value.
func (n *Node) Value() Value {
return n.value
}
// Ref returns this 'cache node' ref counter.
func (n *Node) Ref() int32 {
return atomic.LoadInt32(&n.ref)
}
// GetHandle returns an handle for this 'cache node'.
func (n *Node) GetHandle() *Handle {
if atomic.AddInt32(&n.ref, 1) <= 1 {
panic("BUG: Node.GetHandle on zero ref")
}
return &Handle{unsafe.Pointer(n)}
}
func (n *Node) unref() {
if atomic.AddInt32(&n.ref, -1) == 0 {
n.r.delete(n)
}
}
func (n *Node) unrefLocked() {
if atomic.AddInt32(&n.ref, -1) == 0 {
n.r.mu.RLock()
if !n.r.closed {
n.r.delete(n)
}
n.r.mu.RUnlock()
}
}
// Handle is a 'cache handle' of a 'cache node'.
type Handle struct {
n unsafe.Pointer // *Node
}
// Value returns the value of the 'cache node'.
func (h *Handle) Value() Value {
n := (*Node)(atomic.LoadPointer(&h.n))
if n != nil {
return n.value
}
return nil
}
// Release releases this 'cache handle'.
// It is safe to call release multiple times.
func (h *Handle) Release() {
nPtr := atomic.LoadPointer(&h.n)
if nPtr != nil && atomic.CompareAndSwapPointer(&h.n, nPtr, nil) {
n := (*Node)(nPtr)
n.unrefLocked()
}
}
func murmur32(ns, key uint64, seed uint32) uint32 {
const (
m = uint32(0x5bd1e995)
r = 24
)
k1 := uint32(ns >> 32)
k2 := uint32(ns)
k3 := uint32(key >> 32)
k4 := uint32(key)
k1 *= m
k1 ^= k1 >> r
k1 *= m
k2 *= m
k2 ^= k2 >> r
k2 *= m
k3 *= m
k3 ^= k3 >> r
k3 *= m
k4 *= m
k4 ^= k4 >> r
k4 *= m
h := seed
h *= m
h ^= k1
h *= m
h ^= k2
h *= m
h ^= k3
h *= m
h ^= k4
h ^= h >> 13
h *= m
h ^= h >> 15
return h
}