feat: new experimental gc friendly flatten cache

Signed-off-by: Rueian <rueiancsie@gmail.com>

Author: rueian

Diff for: cache.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"sync"
 	"time"
+	"unsafe"
 )
 
 // NewCacheStoreFn can be provided in ClientOption for using a custom CacheStore implementation
@@ -178,3 +179,222 @@ func (a *adapterEntry) Wait(ctx context.Context) (RedisMessage, error) {
 		return a.val, a.err
 	}
 }
+
+type flatentry struct {
+	ovfl *flatentry
+	next unsafe.Pointer
+	prev unsafe.Pointer
+	cmd  string
+	key  string
+	val  []byte
+	ttl  int64
+	siz  int64
+	mu   sync.Mutex
+	mark int64
+}
+
+func (f *flatentry) insert(e *flatentry) {
+	f.siz += e.siz
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	e.ovfl = f.ovfl
+	f.ovfl = e
+}
+
+func (f *flatentry) find(cmd string, ts int64) (ret RedisMessage, expired bool) {
+	if f == nil {
+		return
+	}
+	if ts >= f.ttl {
+		expired = true
+		return
+	}
+	if cmd == f.cmd {
+		_ = ret.CacheUnmarshalView(f.val)
+		return
+	}
+	f.mu.Lock()
+	ovfl := f.ovfl
+	f.mu.Unlock()
+	return ovfl.find(cmd, ts)
+}
+
+const lrBatchSize = 64
+
+type lrBatch struct {
+	m map[*flatentry]struct{}
+}
+
+func NewFlattenCache(limit int64) CacheStore {
+	f := &flatten{
+		flights: make(map[string]*adapterEntry),
+		cache:   make(map[string]*flatentry),
+		head:    &flatentry{},
+		tail:    &flatentry{},
+		size:    0,
+		limit:   limit,
+	}
+	f.head.next = unsafe.Pointer(f.tail)
+	f.tail.prev = unsafe.Pointer(f.head)
+	f.lrup = sync.Pool{New: func() any {
+		return &lrBatch{m: make(map[*flatentry]struct{}, lrBatchSize)}
+	}}
+	return f
+}
+
+type flatten struct {
+	flights map[string]*adapterEntry
+	cache   map[string]*flatentry
+	head    *flatentry
+	tail    *flatentry
+	lrup    sync.Pool
+	mark    int64
+	size    int64
+	limit   int64
+	mu      sync.RWMutex
+}
+
+func (f *flatten) llAdd(e *flatentry) {
+	e.mark = f.mark
+	e.prev = f.tail.prev
+	e.next = unsafe.Pointer(f.tail)
+	f.tail.prev = unsafe.Pointer(e)
+	(*flatentry)(e.prev).next = unsafe.Pointer(e)
+}
+
+func (f *flatten) llDel(e *flatentry) {
+	(*flatentry)(e.prev).next = e.next
+	(*flatentry)(e.next).prev = e.prev
+	e.mark = 0
+}
+
+func (f *flatten) llTail(e *flatentry) {
+	f.llDel(e)
+	f.llAdd(e)
+}
+
+func (f *flatten) remove(e *flatentry) {
+	f.size -= e.siz
+	f.llDel(e)
+	delete(f.cache, e.key)
+}
+
+func (f *flatten) Flight(key, cmd string, ttl time.Duration, now time.Time) (RedisMessage, CacheEntry) {
+	f.mu.RLock()
+	e := f.cache[key]
+	f.mu.RUnlock()
+	ts := now.UnixMilli()
+	if v, _ := e.find(cmd, ts); v.typ != 0 {
+		batch := f.lrup.Get().(*lrBatch)
+		batch.m[e] = struct{}{}
+		if len(batch.m) == lrBatchSize {
+			f.mu.Lock()
+			for e := range batch.m {
+				if e.mark == f.mark {
+					f.llTail(e)
+				}
+			}
+			f.mu.Unlock()
+			clear(batch.m)
+		}
+		f.lrup.Put(batch)
+		return v, nil
+	}
+	fk := key + cmd
+	f.mu.RLock()
+	af := f.flights[fk]
+	f.mu.RUnlock()
+	if af != nil {
+		return RedisMessage{}, af
+	}
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	e = f.cache[key]
+	v, expired := e.find(cmd, ts)
+	if v.typ != 0 {
+		f.llTail(e)
+		return v, nil
+	}
+	if expired {
+		f.remove(e)
+	}
+	if af = f.flights[fk]; af != nil {
+		return RedisMessage{}, af
+	}
+	f.flights[fk] = &adapterEntry{ch: make(chan struct{}), xat: ts + ttl.Milliseconds()}
+	return RedisMessage{}, nil
+}
+
+func (f *flatten) Update(key, cmd string, val RedisMessage) int64 {
+	fk := key + cmd
+	bs := val.CacheMarshal(nil)
+	fe := &flatentry{cmd: cmd, val: bs, ttl: val.CachePXAT(), siz: int64(len(bs)+len(key)+len(cmd)) + int64(unsafe.Sizeof(flatentry{}))}
+	f.mu.Lock()
+	af := f.flights[fk]
+	if af != nil {
+		delete(f.flights, fk)
+		if af.xat < fe.ttl {
+			fe.ttl = af.xat
+		}
+	}
+	f.size += fe.siz
+	for ep := f.head.next; f.size > f.limit && ep != unsafe.Pointer(f.tail); {
+		e := (*flatentry)(ep)
+		f.remove(e)
+		ep = e.next
+	}
+	if e := f.cache[key]; e == nil {
+		fe.key = key
+		f.cache[key] = fe
+		f.llAdd(fe)
+	} else {
+		e.insert(fe)
+	}
+	f.mu.Unlock()
+	if af != nil {
+		af.set(val, nil)
+	}
+	return fe.ttl
+}
+
+func (f *flatten) Cancel(key, cmd string, err error) {
+	fk := key + cmd
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	if af := f.flights[fk]; af != nil {
+		delete(f.flights, fk)
+		af.set(RedisMessage{}, err)
+	}
+}
+
+func (f *flatten) Delete(keys []RedisMessage) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	if keys == nil {
+		f.cache = make(map[string]*flatentry, len(f.cache))
+		f.head.next = unsafe.Pointer(f.tail)
+		f.tail.prev = unsafe.Pointer(f.head)
+		f.mark++
+		f.size = 0
+	} else {
+		for _, k := range keys {
+			if e := f.cache[k.string]; e != nil {
+				f.remove(e)
+			}
+		}
+	}
+}
+
+func (f *flatten) Close(err error) {
+	f.mu.Lock()
+	flights := f.flights
+	f.flights = nil
+	f.cache = nil
+	f.tail = nil
+	f.head = nil
+	f.mark++
+	f.mu.Unlock()
+	for _, entry := range flights {
+		entry.set(RedisMessage{}, err)
+	}
+}