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/*
* Copyright 2021 ByteDance Inc.
*
* 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 caching
import (
`sync`
`sync/atomic`
`unsafe`
`github.com/bytedance/sonic/internal/rt`
)
/** Program Map **/
const (
_LoadFactor = 0.5
_InitCapacity = 4096 // must be a power of 2
)
type _ProgramMap struct {
n uint64
m uint32
b []_ProgramEntry
}
type _ProgramEntry struct {
vt *rt.GoType
fn interface{}
}
func newProgramMap() *_ProgramMap {
return &_ProgramMap {
n: 0,
m: _InitCapacity - 1,
b: make([]_ProgramEntry, _InitCapacity),
}
}
func (self *_ProgramMap) copy() *_ProgramMap {
fork := &_ProgramMap{
n: self.n,
m: self.m,
b: make([]_ProgramEntry, len(self.b)),
}
for i, f := range self.b {
fork.b[i] = f
}
return fork
}
func (self *_ProgramMap) get(vt *rt.GoType) interface{} {
i := self.m + 1
p := vt.Hash & self.m
/* linear probing */
for ; i > 0; i-- {
if b := self.b[p]; b.vt == vt {
return b.fn
} else if b.vt == nil {
break
} else {
p = (p + 1) & self.m
}
}
/* not found */
return nil
}
func (self *_ProgramMap) add(vt *rt.GoType, fn interface{}) *_ProgramMap {
p := self.copy()
f := float64(atomic.LoadUint64(&p.n) + 1) / float64(p.m + 1)
/* check for load factor */
if f > _LoadFactor {
p = p.rehash()
}
/* insert the value */
p.insert(vt, fn)
return p
}
func (self *_ProgramMap) rehash() *_ProgramMap {
c := (self.m + 1) << 1
r := &_ProgramMap{m: c - 1, b: make([]_ProgramEntry, int(c))}
/* rehash every entry */
for i := uint32(0); i <= self.m; i++ {
if b := self.b[i]; b.vt != nil {
r.insert(b.vt, b.fn)
}
}
/* rebuild successful */
return r
}
func (self *_ProgramMap) insert(vt *rt.GoType, fn interface{}) {
h := vt.Hash
p := h & self.m
/* linear probing */
for i := uint32(0); i <= self.m; i++ {
if b := &self.b[p]; b.vt != nil {
p += 1
p &= self.m
} else {
b.vt = vt
b.fn = fn
atomic.AddUint64(&self.n, 1)
return
}
}
/* should never happens */
panic("no available slots")
}
/** RCU Program Cache **/
type ProgramCache struct {
m sync.Mutex
p unsafe.Pointer
}
func CreateProgramCache() *ProgramCache {
return &ProgramCache {
m: sync.Mutex{},
p: unsafe.Pointer(newProgramMap()),
}
}
func (self *ProgramCache) Get(vt *rt.GoType) interface{} {
return (*_ProgramMap)(atomic.LoadPointer(&self.p)).get(vt)
}
func (self *ProgramCache) Compute(vt *rt.GoType, compute func(*rt.GoType, ... interface{}) (interface{}, error), ex ...interface{}) (interface{}, error) {
var err error
var val interface{}
/* use defer to prevent inlining of this function */
self.m.Lock()
defer self.m.Unlock()
/* double check with write lock held */
if val = self.Get(vt); val != nil {
return val, nil
}
/* compute the value */
if val, err = compute(vt, ex...); err != nil {
return nil, err
}
/* update the RCU cache */
atomic.StorePointer(&self.p, unsafe.Pointer((*_ProgramMap)(atomic.LoadPointer(&self.p)).add(vt, val)))
return val, nil
}
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