75 lines
2.1 KiB
Go
75 lines
2.1 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 android
|
|
|
|
import (
|
|
"fmt"
|
|
"sync"
|
|
)
|
|
|
|
type OncePer struct {
|
|
values sync.Map
|
|
valuesLock sync.Mutex
|
|
}
|
|
|
|
type valueMap map[interface{}]interface{}
|
|
|
|
// Once computes a value the first time it is called with a given key per OncePer, and returns the
|
|
// value without recomputing when called with the same key. key must be hashable.
|
|
func (once *OncePer) Once(key interface{}, value func() interface{}) interface{} {
|
|
// Fast path: check if the key is already in the map
|
|
if v, ok := once.values.Load(key); ok {
|
|
return v
|
|
}
|
|
|
|
// Slow path: lock so that we don't call the value function twice concurrently
|
|
once.valuesLock.Lock()
|
|
defer once.valuesLock.Unlock()
|
|
|
|
// Check again with the lock held
|
|
if v, ok := once.values.Load(key); ok {
|
|
return v
|
|
}
|
|
|
|
// Still not in the map, call the value function and store it
|
|
v := value()
|
|
once.values.Store(key, v)
|
|
|
|
return v
|
|
}
|
|
|
|
func (once *OncePer) Get(key interface{}) interface{} {
|
|
v, ok := once.values.Load(key)
|
|
if !ok {
|
|
panic(fmt.Errorf("Get() called before Once()"))
|
|
}
|
|
|
|
return v
|
|
}
|
|
|
|
func (once *OncePer) OnceStringSlice(key interface{}, value func() []string) []string {
|
|
return once.Once(key, func() interface{} { return value() }).([]string)
|
|
}
|
|
|
|
func (once *OncePer) Once2StringSlice(key interface{}, value func() ([]string, []string)) ([]string, []string) {
|
|
type twoStringSlice [2][]string
|
|
s := once.Once(key, func() interface{} {
|
|
var s twoStringSlice
|
|
s[0], s[1] = value()
|
|
return s
|
|
}).(twoStringSlice)
|
|
return s[0], s[1]
|
|
}
|