mirror of
https://github.com/ceph/ceph-csi.git
synced 2024-11-25 15:50:20 +00:00
84 lines
2.2 KiB
Go
84 lines
2.2 KiB
Go
|
/*
|
||
|
|
Copyright 2023 The Kubernetes Authors.
|
||
|
|
|
||
|
|
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 synctrack
|
||
|
|
|
||
|
|
import (
|
||
|
|
"sync"
|
||
|
|
"sync/atomic"
|
||
|
|
)
|
||
|
|
|
||
|
|
// Lazy defers the computation of `Evaluate` to when it is necessary. It is
|
||
|
|
// possible that Evaluate will be called in parallel from multiple goroutines.
|
||
|
|
type Lazy[T any] struct {
|
||
|
|
Evaluate func() (T, error)
|
||
|
|
|
||
|
|
cache atomic.Pointer[cacheEntry[T]]
|
||
|
|
}
|
||
|
|
|
||
|
|
type cacheEntry[T any] struct {
|
||
|
|
eval func() (T, error)
|
||
|
|
lock sync.RWMutex
|
||
|
|
result *T
|
||
|
|
}
|
||
|
|
|
||
|
|
func (e *cacheEntry[T]) get() (T, error) {
|
||
|
|
if cur := func() *T {
|
||
|
|
e.lock.RLock()
|
||
|
|
defer e.lock.RUnlock()
|
||
|
|
return e.result
|
||
|
|
}(); cur != nil {
|
||
|
|
return *cur, nil
|
||
|
|
}
|
||
|
|
|
||
|
|
e.lock.Lock()
|
||
|
|
defer e.lock.Unlock()
|
||
|
|
if e.result != nil {
|
||
|
|
return *e.result, nil
|
||
|
|
}
|
||
|
|
r, err := e.eval()
|
||
|
|
if err == nil {
|
||
|
|
e.result = &r
|
||
|
|
}
|
||
|
|
return r, err
|
||
|
|
}
|
||
|
|
|
||
|
|
func (z *Lazy[T]) newCacheEntry() *cacheEntry[T] {
|
||
|
|
return &cacheEntry[T]{eval: z.Evaluate}
|
||
|
|
}
|
||
|
|
|
||
|
|
// Notify should be called when something has changed necessitating a new call
|
||
|
|
// to Evaluate.
|
||
|
|
func (z *Lazy[T]) Notify() { z.cache.Swap(z.newCacheEntry()) }
|
||
|
|
|
||
|
|
// Get should be called to get the current result of a call to Evaluate. If the
|
||
|
|
// current cached value is stale (due to a call to Notify), then Evaluate will
|
||
|
|
// be called synchronously. If subsequent calls to Get happen (without another
|
||
|
|
// Notify), they will all wait for the same return value.
|
||
|
|
//
|
||
|
|
// Error returns are not cached and will cause multiple calls to evaluate!
|
||
|
|
func (z *Lazy[T]) Get() (T, error) {
|
||
|
|
e := z.cache.Load()
|
||
|
|
if e == nil {
|
||
|
|
// Since we don't force a constructor, nil is a possible value.
|
||
|
|
// If multiple Gets race to set this, the swap makes sure only
|
||
|
|
// one wins.
|
||
|
|
z.cache.CompareAndSwap(nil, z.newCacheEntry())
|
||
|
|
e = z.cache.Load()
|
||
|
|
}
|
||
|
|
return e.get()
|
||
|
|
}
|