直接上代码:
1. 第一种情况, 如果没有select{}, main 主线程不会等待coroutine运行,导致coroutine得不到机会运行。
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, 程序正常运行。
package main import ( "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有机会运行,但是会发生死锁,fatal error: all goroutines are asleep - deadlock!
The goroutine executing func1 exited,ditto for func2. The maingoroutine is blocked with no hope to recover while no other goroutinecan be scheduled.
package main import ( "fmt" //"time" ) func main() { go func1() go func2() select { } } func func1() { fmt.Println("here1") } func func2() { fmt.Println("here2") }
3. 第三种情况, 正常运行。
package main import ( "fmt" ) var c = make(chan int,2) func main() { go func1() go func2() <-c <-c fmt.Println("ok") } func func1() { fmt.Println("here1") c <- 1 } func func2() { fmt.Println("here2") c <- 1 }
4. 实现上面的目的的另外一种方法:
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()