From cdffce3865a987594d233b79f03d2a0954507f79 Mon Sep 17 00:00:00 2001
From: "feixiao2020@sina.com" <fx@arcvideo.com>
Date: Mon, 25 May 2020 15:31:52 +0800
Subject: [PATCH] =?UTF-8?q?=E8=A7=A3=E8=AF=BB=E9=98=B2=E6=AD=A2=E7=BC=93?=
 =?UTF-8?q?=E5=AD=98=E5=87=BB=E7=A9=BF=E4=BB=A3=E7=A0=81=E5=AD=A6=E4=B9=A0?=
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---
 singleflight/singleflight.go | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/singleflight/singleflight.go b/singleflight/singleflight.go
index ff2c2ee..0dc74eb 100644
--- a/singleflight/singleflight.go
+++ b/singleflight/singleflight.go
@@ -21,6 +21,7 @@ package singleflight
 import "sync"
 
 // call is an in-flight or completed Do call
+// 包装一个key获取值锁需要的一些参数
 type call struct {
 	wg  sync.WaitGroup
 	val interface{}
@@ -43,19 +44,24 @@ func (g *Group) Do(key string, fn func() (interface{}, error)) (interface{}, err
 	if g.m == nil {
 		g.m = make(map[string]*call)
 	}
+
 	if c, ok := g.m[key]; ok {
+		// 已经有协程在处理了，阻塞(c.wg.Wait())等待完成
 		g.mu.Unlock()
 		c.wg.Wait()
 		return c.val, c.err
 	}
+	// 目前没有协程在处理，新建一个处理的任务
 	c := new(call)
 	c.wg.Add(1)
 	g.m[key] = c
 	g.mu.Unlock()
 
+	// 执行获取key的函数，并将结果赋值给这个Call
 	c.val, c.err = fn()
 	c.wg.Done()
 
+	// 重新上锁删除key
 	g.mu.Lock()
 	delete(g.m, key)
 	g.mu.Unlock()