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cache.go
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cache.go
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// Copyright 2017 Monax Industries Limited
//
// 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 names
import (
"fmt"
"sort"
"sync"
)
// The Cache helps prevent unnecessary IAVLTree updates and garbage generation.
type Cache struct {
sync.RWMutex
backend Reader
names map[string]*nameInfo
}
type nameInfo struct {
sync.RWMutex
entry *Entry
removed bool
updated bool
}
var _ Writer = &Cache{}
// Returns a Cache that wraps an underlying NameRegCacheGetter to use on a cache miss, can write to an
// output Writer via Sync.
// Not goroutine safe, use syncStateCache if you need concurrent access
func NewCache(backend Reader) *Cache {
return &Cache{
backend: backend,
names: make(map[string]*nameInfo),
}
}
func (cache *Cache) GetName(name string) (*Entry, error) {
nameInfo, err := cache.get(name)
if err != nil {
return nil, err
}
nameInfo.RLock()
defer nameInfo.RUnlock()
if nameInfo.removed {
return nil, nil
}
return nameInfo.entry, nil
}
func (cache *Cache) UpdateName(entry *Entry) error {
nameInfo, err := cache.get(entry.Name)
if err != nil {
return err
}
nameInfo.Lock()
defer nameInfo.Unlock()
if nameInfo.removed {
return fmt.Errorf("UpdateName on a removed name: %s", nameInfo.entry.Name)
}
nameInfo.entry = entry
nameInfo.updated = true
return nil
}
func (cache *Cache) RemoveName(name string) error {
nameInfo, err := cache.get(name)
if err != nil {
return err
}
nameInfo.Lock()
defer nameInfo.Unlock()
if nameInfo.removed {
return fmt.Errorf("RemoveName on removed name: %s", name)
}
nameInfo.removed = true
return nil
}
// Writes whatever is in the cache to the output Writer state. Does not flush the cache, to do that call Reset()
// after Sync or use Flusth if your wish to use the output state as your next backend
func (cache *Cache) Sync(state Writer) error {
cache.Lock()
defer cache.Unlock()
// Determine order for names
// note names may be of any length less than some limit
var names sort.StringSlice
for nameStr := range cache.names {
names = append(names, nameStr)
}
sort.Stable(names)
// Update or delete names.
for _, name := range names {
nameInfo := cache.names[name]
nameInfo.RLock()
if nameInfo.removed {
err := state.RemoveName(name)
if err != nil {
nameInfo.RUnlock()
return err
}
} else if nameInfo.updated {
err := state.UpdateName(nameInfo.entry)
if err != nil {
nameInfo.RUnlock()
return err
}
}
nameInfo.RUnlock()
}
return nil
}
// Resets the cache to empty initialising the backing map to the same size as the previous iteration.
func (cache *Cache) Reset(backend Reader) {
cache.Lock()
defer cache.Unlock()
cache.backend = backend
cache.names = make(map[string]*nameInfo)
}
// Syncs the Cache and Resets it to use Writer as the backend Reader
func (cache *Cache) Flush(output Writer, backend Reader) error {
err := cache.Sync(output)
if err != nil {
return err
}
cache.Reset(backend)
return nil
}
func (cache *Cache) Backend() Reader {
return cache.backend
}
// Get the cache accountInfo item creating it if necessary
func (cache *Cache) get(name string) (*nameInfo, error) {
cache.RLock()
nmeInfo := cache.names[name]
cache.RUnlock()
if nmeInfo == nil {
cache.Lock()
defer cache.Unlock()
nmeInfo = cache.names[name]
if nmeInfo == nil {
entry, err := cache.backend.GetName(name)
if err != nil {
return nil, err
}
nmeInfo = &nameInfo{
entry: entry,
}
cache.names[name] = nmeInfo
}
}
return nmeInfo, nil
}