59 lines
1.7 KiB
Go
59 lines
1.7 KiB
Go
// Copyright 2016 Google Inc. All Rights Reserved.
|
|
//
|
|
// 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 atomiccache provides a map-based cache that supports very fast
|
|
// reads.
|
|
package atomiccache
|
|
|
|
import (
|
|
"sync"
|
|
"sync/atomic"
|
|
)
|
|
|
|
type mapType map[interface{}]interface{}
|
|
|
|
// Cache is a map-based cache that supports fast reads via use of atomics.
|
|
// Writes are slow, requiring a copy of the entire cache.
|
|
// The zero Cache is an empty cache, ready for use.
|
|
type Cache struct {
|
|
val atomic.Value // mapType
|
|
mu sync.Mutex // used only by writers
|
|
}
|
|
|
|
// Get returns the value of the cache at key. If there is no value,
|
|
// getter is called to provide one, and the cache is updated.
|
|
// The getter function may be called concurrently. It should be pure,
|
|
// returning the same value for every call.
|
|
func (c *Cache) Get(key interface{}, getter func() interface{}) interface{} {
|
|
mp, _ := c.val.Load().(mapType)
|
|
if v, ok := mp[key]; ok {
|
|
return v
|
|
}
|
|
|
|
// Compute value without lock.
|
|
// Might duplicate effort but won't hold other computations back.
|
|
newV := getter()
|
|
|
|
c.mu.Lock()
|
|
mp, _ = c.val.Load().(mapType)
|
|
newM := make(mapType, len(mp)+1)
|
|
for k, v := range mp {
|
|
newM[k] = v
|
|
}
|
|
newM[key] = newV
|
|
c.val.Store(newM)
|
|
c.mu.Unlock()
|
|
return newV
|
|
}
|