| // Copyright 2013 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| package net |
| |
| import "sync" |
| |
| // call is an in-flight or completed singleflight.Do call |
| type call struct { |
| wg sync.WaitGroup |
| val interface{} |
| err error |
| dups int |
| } |
| |
| // singleflight represents a class of work and forms a namespace in |
| // which units of work can be executed with duplicate suppression. |
| type singleflight struct { |
| mu sync.Mutex // protects m |
| m map[string]*call // lazily initialized |
| } |
| |
| // Do executes and returns the results of the given function, making |
| // sure that only one execution is in-flight for a given key at a |
| // time. If a duplicate comes in, the duplicate caller waits for the |
| // original to complete and receives the same results. |
| // The return value shared indicates whether v was given to multiple callers. |
| func (g *singleflight) Do(key string, fn func() (interface{}, error)) (v interface{}, err error, shared bool) { |
| g.mu.Lock() |
| if g.m == nil { |
| g.m = make(map[string]*call) |
| } |
| if c, ok := g.m[key]; ok { |
| c.dups++ |
| g.mu.Unlock() |
| c.wg.Wait() |
| return c.val, c.err, true |
| } |
| c := new(call) |
| c.wg.Add(1) |
| g.m[key] = c |
| g.mu.Unlock() |
| |
| c.val, c.err = fn() |
| c.wg.Done() |
| |
| g.mu.Lock() |
| delete(g.m, key) |
| g.mu.Unlock() |
| |
| return c.val, c.err, c.dups > 0 |
| } |