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checklist.go
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checklist.go
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//
// Copyright (C) 2019-2020 Vdaas.org Vald team ( kpango, rinx, kmrmt )
//
// 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
//
// https://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 grpc
import (
"sync"
"sync/atomic"
"unsafe"
)
type checkList struct {
mu sync.Mutex
read atomic.Value
dirty map[string]*entryCheckList
misses int
}
type readOnlyCheckList struct {
m map[string]*entryCheckList
amended bool
}
var expungedCheckList = unsafe.Pointer(new(struct{}))
type entryCheckList struct {
p unsafe.Pointer
}
func (m *checkList) Exists(key string) bool {
read, _ := m.read.Load().(readOnlyCheckList)
e, ok := read.m[key]
if !ok && read.amended {
m.mu.Lock()
read, _ = m.read.Load().(readOnlyCheckList)
e, ok = read.m[key]
if !ok && read.amended {
e, ok = m.dirty[key]
m.missLocked()
}
m.mu.Unlock()
}
if !ok {
return false
}
p := atomic.LoadPointer(&e.p)
if p == nil || p == expungedCheckList {
return false
}
return true
}
func (m *checkList) Check(key string) {
value := struct{}{}
read, _ := m.read.Load().(readOnlyCheckList)
if e, ok := read.m[key]; ok && e.tryStore(&value) {
return
}
m.mu.Lock()
read, _ = m.read.Load().(readOnlyCheckList)
if e, ok := read.m[key]; ok {
if e.unexpungeLocked() {
m.dirty[key] = e
}
atomic.StorePointer(&e.p, unsafe.Pointer(&value))
} else if e, ok := m.dirty[key]; ok {
atomic.StorePointer(&e.p, unsafe.Pointer(&value))
} else {
if !read.amended {
m.dirtyLocked()
m.read.Store(readOnlyCheckList{m: read.m, amended: true})
}
m.dirty[key] = &entryCheckList{p: unsafe.Pointer(&value)}
}
m.mu.Unlock()
}
func (e *entryCheckList) tryStore(i *struct{}) bool {
for {
p := atomic.LoadPointer(&e.p)
if p == expungedCheckList {
return false
}
if atomic.CompareAndSwapPointer(&e.p, p, unsafe.Pointer(i)) {
return true
}
}
}
func (e *entryCheckList) unexpungeLocked() (wasExpunged bool) {
return atomic.CompareAndSwapPointer(&e.p, expungedCheckList, nil)
}
func (m *checkList) missLocked() {
m.misses++
if m.misses < len(m.dirty) {
return
}
m.read.Store(readOnlyCheckList{m: m.dirty})
m.dirty = nil
m.misses = 0
}
func (m *checkList) dirtyLocked() {
if m.dirty != nil {
return
}
read, _ := m.read.Load().(readOnlyCheckList)
m.dirty = make(map[string]*entryCheckList, len(read.m))
for k, e := range read.m {
if !e.tryExpungeLocked() {
m.dirty[k] = e
}
}
}
func (e *entryCheckList) tryExpungeLocked() (isExpunged bool) {
p := atomic.LoadPointer(&e.p)
for p == nil {
if atomic.CompareAndSwapPointer(&e.p, nil, expungedCheckList) {
return true
}
p = atomic.LoadPointer(&e.p)
}
return p == expungedCheckList
}