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| 1 // Copyright 2013 The Go Authors. All rights reserved. |
| 2 // Use of this source code is governed by a BSD-style |
| 3 // license that can be found in the LICENSE file. |
| 4 |
| 5 package net |
| 6 |
| 7 import "sync" |
| 8 |
| 9 // call is an in-flight or completed singleflight.Do call |
| 10 type call struct { |
| 11 wg sync.WaitGroup |
| 12 val interface{} |
| 13 err error |
| 14 dups int |
| 15 } |
| 16 |
| 17 // singleflight represents a class of work and forms a namespace in |
| 18 // which units of work can be executed with duplicate suppression. |
| 19 type singleflight struct { |
| 20 mu sync.Mutex // protects m |
| 21 m map[string]*call // lazily initialized |
| 22 } |
| 23 |
| 24 // Do executes and returns the results of the given function, making |
| 25 // sure that only one execution is in-flight for a given key at a |
| 26 // time. If a duplicate comes in, the duplicate caller waits for the |
| 27 // original to complete and receives the same results. |
| 28 // The return value shared indicates whether v was given to multiple callers. |
| 29 func (g *singleflight) Do(key string, fn func() (interface{}, error)) (v interfa
ce{}, err error, shared bool) { |
| 30 g.mu.Lock() |
| 31 if g.m == nil { |
| 32 g.m = make(map[string]*call) |
| 33 } |
| 34 if c, ok := g.m[key]; ok { |
| 35 c.dups++ |
| 36 g.mu.Unlock() |
| 37 c.wg.Wait() |
| 38 return c.val, c.err, true |
| 39 } |
| 40 c := new(call) |
| 41 c.wg.Add(1) |
| 42 g.m[key] = c |
| 43 g.mu.Unlock() |
| 44 |
| 45 c.val, c.err = fn() |
| 46 c.wg.Done() |
| 47 |
| 48 g.mu.Lock() |
| 49 delete(g.m, key) |
| 50 g.mu.Unlock() |
| 51 |
| 52 return c.val, c.err, c.dups > 0 |
| 53 } |
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