/
singleflight.go
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/
singleflight.go
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//
// Copyright (C) 2019-2021 vdaas.org vald team <vald@vdaas.org>
//
// 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 singleflight represents zero time caching.
package singleflight
import (
"context"
"sync"
"sync/atomic"
)
type call struct {
wg sync.WaitGroup
val interface{}
err error
dups uint64
}
// Group represents interface for zero time cache.
type Group interface {
Do(ctx context.Context, key string, fn func() (interface{}, error)) (v interface{}, shared bool, err error)
}
type group struct {
m sync.Map
}
// New returns Group implementation.
func New() Group {
return new(group)
}
// Do execute the given function and return the result.
// It makes sure only one execution of the function for each given key.
// If duplicate comes, the duplicated call with the same key will wait for the first caller return.
// It returns the result and the error of the given function, and whether the result is shared from the first caller.
func (g *group) Do(ctx context.Context, key string, fn func() (interface{}, error)) (v interface{}, shared bool, err error) {
actual, loaded := g.m.LoadOrStore(key, new(call))
c := actual.(*call)
if loaded {
atomic.AddUint64(&c.dups, 1)
c.wg.Wait()
v, err = c.val, c.err
return v, true, err
}
c.wg.Add(1)
c.val, c.err = fn()
c.wg.Done()
g.m.LoadAndDelete(key)
return c.val, atomic.LoadUint64(&c.dups) > 0, c.err
}