Goroutine退出時如何安全調用清理函數?

今天遇到一個問題(應該算是坑吧):

在Goroutine中退出時defer調用RPC的Close函數, 可是server老是提示網絡非正常退出.

最終發現是Goroutine退出時調用Close可能致使阻塞, 阻塞致使Goroutine切換到main.

main 退出後程序就終止了.

我構造了一個相似的例子:

package main

import (
	"log"
	"time"
)

func worker(quit <-chan bool) {
	defer func() {
		// 若是被調用函數內部可能阻塞的話
		// 將不能保證被徹底執行
		time.Sleep(time.Second)
		log.Println("worker clean up")
	}()

	for {
		select {
		case <-quit:
			log.Println("worker quit ...")
			return
		default:
		}
	}
}

func main() {
	quit := make(chan bool)
	go worker(quit)
	quit <- true
}

我目前想到的安全作法是: 再設置一個done管道, 在main函數中阻塞等待Goroutine清理工做所有完成.

更好的等待Goroutine完成的方法是用sync.WaitGroup:

// This example fetches several URLs concurrently,
// using a WaitGroup to block until all the fetches are complete.
func ExampleWaitGroup() {
	var wg sync.WaitGroup
	var urls = []string{
		"http://www.golang.org/",
		"http://www.google.com/",
		"http://www.somestupidname.com/",
	}
	for _, url := range urls {
		// Increment the WaitGroup counter.
		wg.Add(1)
		// Launch a goroutine to fetch the URL.
		go func(url string) {
			// Decrement the counter when the goroutine completes.
			defer wg.Done()
			// Fetch the URL.
			http.Get(url)
		}(url)
	}
	// Wait for all HTTP fetches to complete.
	wg.Wait()
}

關於sync.WaitGroup文檔請參考: http://golang.org/pkg/sync/#WaitGroup