add: waitgroup的几种用法

waitgroup/example2/main.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"sync"
+	"time"
+)
+
+/*
+限制并发数量的用法
+*/
+func main() {
+	wg := sync.WaitGroup{}
+	// 最多允许的并发数量
+	limit := make(chan struct{}, 20)
+	for i := 0; i < 100; i++ {
+		wg.Add(1)
+		limit <- struct{}{}
+		go func(num int) {
+			defer func() {
+				<-limit
+				wg.Done()
+			}()
+			dosth(num)
+		}(i)
+	}
+	wg.Wait()
+}
+
+func dosth(i int) {
+	fmt.Println("do sth-->", strconv.Itoa(i))
+	// 模拟耗时1s
+	time.Sleep(time.Second)
+}

waitgroup/example2/readme.md

@@ -0,0 +1 @@
+> 用waitgroup限制并发数量的用法