golang coroutine 的等待與死結

這是一個建立於 的文章，其中的資訊可能已經有所發展或是發生改變。

直接上代碼：

1. 第一種情況， 如果沒有select{}， main 主線程不會等待coroutine運行，導致coroutine得不到機會運行。

You are requesting eventual scheduling (using the two go statements) 
of two goroutines and then you exit main without giving the scheduler 
a chance to do anything. 

有了select， 程式正常運行。

package mainimport ("fmt"        "time")func main() {go func1()go func2()select{}}func func1() {       for{    fmt.Println("here1")            time.Sleep(10 * time.Minute)        }}func func2() {       for{   fmt.Println("here2")           time.Sleep(10 * time.Minute)       }

}

2. coroutine有機會運行，但是會發生死結， fatal error: all goroutines are asleep - deadlock!

The goroutine executing func1 exited, ditto for func2. The main goroutine is blocked with no hope to recover while no other goroutine can be scheduled.

package mainimport ("fmt"//"time")func main() {go func1()go func2()select {}}func func1() {fmt.Println("here1")}func func2() {fmt.Println("here2")}

3. 第三種情況， 正常運行。

package mainimport ("fmt")var c = make(chan int, 2)func main() {go func1()go func2()<-c<-cfmt.Println("ok")}func func1() {fmt.Println("here1")c <- 1}func func2() {fmt.Println("here2")c <- 1}

4. 實現上面的目的的另外一種方法：

  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()