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 main goroutine is blocked with no hope to recover while no other goroutine can 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()
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