Goroutine退出时如何安全调用清理函数?

今天遇到一个问题(应该算是坑吧):

在Goroutine中退出时defer调用RPC的Close函数, 但是server总是提示网络非正常退出.

最终发现是Goroutine退出时调用Close可能导致阻塞, 阻塞导致Goroutine切换到main.

main 退出后程序就终止了.

我构造了一个类似的例子:

package main

import (
    "log"
    "time"
)

func worker(quit <-chan bool) {
    defer func() {
        // 如果被调用函数内部可能阻塞的话
        // 将不能保证被完全执行
        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
}

我目前想到的安全做法是: 再设置一个done管道, 在main函数中阻塞等待Goroutine清理工作全部完成.

更好的等待Goroutine完成的方法是用sync.WaitGroup:

        "http://www.golang.org/",
// 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()
}

关于sync.WaitGroup文档请参考: http://golang.org/pkg/sync/#WaitGroup