英文:
Why aren't my goroutines launched?
问题
不，不是因为我的程序结束得太快。
我有这个脚本：
package main
import ("log"; "io/ioutil"; "strings")
const BASE_FILE_NAME = "abc_"
func mygoroutine(file_name string) {
log.Println("在文件", file_name, "的goroutine中")
}
func get_file_names() []string {
file_names := make([]string, 0)
files, _ := ioutil.ReadDir("./")
for _, file := range files {
if strings.HasPrefix(file.Name(), BASE_FILE_NAME) {
file_names = append(file_names, file.Name())
}
}
return file_names
}
func main() {
file_names := get_file_names()
for _, file_name := range file_names {
log.Println("现在启动文件", file_name, "的goroutine")
go mygoroutine(file_name)
}
log.Println("启动完成。")
for {}
log.Println("现在退出")
}
在包含可执行文件的目录中，我有两个以abc_开头的文件，所以输出结果是：
2016/03/04 20:35:14 现在启动文件 abc_fr 的goroutine
2016/03/04 20:35:14 现在启动文件 abc_hrty 的goroutine
2016/03/04 20:35:14 启动完成。
脚本不会停止，它永远不会记录现在退出的消息，因为它在空的for循环中循环。但是我没有看到In goroutine for file的消息。
为什么会这样？我做错了什么？
谢谢帮助！
英文:
No, it's not because my program ends too fast.
I have this script:
package main
import ("log"; "io/ioutil"; "strings")
const BASE_FILE_NAME = "abc_"
func mygoroutine(file_name string) {
log.Println("In goroutine for file", file_name)
}
func get_file_names() []string {
file_names := make([]string, 0)
files, _ := ioutil.ReadDir("./")
for _, file := range files {
if strings.HasPrefix(file.Name(), BASE_FILE_NAME) {
file_names = append(file_names, file.Name())
}
}
return file_names
}
func main() {
file_names := get_file_names()
for _, file_name := range file_names {
log.Println("Now lunching goroutine for file", file_name)
go mygoroutine(file_name)
}
log.Println("Finished launching.")
for {}
log.Println("Now exiting")
}
In the directory that contains the executable, I have two files that start with abc_ so the output is this:
2016/03/04 20:35:14 Now lunching goroutine for file abc_fr
2016/03/04 20:35:14 Now lunching goroutine for file abc_hrty
2016/03/04 20:35:14 Finished launching.
The script doesn't stop, it never logs Now exiting , because it loops in the empty for. But I do not see the In goroutine for file message.
Why is this happening? What am I doing wrong?
Thanks for the help!
答案1
得分: 6
如果你的程序在GOMAXPROCS=1（即单个操作系统线程）下运行，for{}会导致它冻结，从而不会让Go的用户模式调度器运行。这是与此相关的问题。JimB指出，无论GOMAXPROCS如何，它都会引起其他问题；最终，运行时必须停止你的goroutine进行垃圾回收，但它无法停止for{}。
将for{}更改为select{}可以让调度器运行，并且不会占用CPU。在这个简化的程序中，你的goroutine代码会运行。它以"all goroutines are asleep - deadlock!"结束，因为你的其他goroutine退出了，只剩下一个（main）goroutine被挂在select{}上。
package main
import "log"
const BASE_FILE_NAME = "abc_"
func mygoroutine(file_name string) {
log.Println("In goroutine for file", file_name)
}
func main() {
go mygoroutine("foo")
log.Println("Finished launching.")
select {}
log.Println("Now exiting")
}
当然，通常情况下，即使使用select{}也不希望让goroutine挂起；这会导致一些资源在程序结束之前一直被占用。要构建有用的东西，你需要使用其他东西，比如sync.WaitGroup或通道。
英文:
If your program is running with GOMAXPROCS=1 (that is, a single OS thread), for{} freezes it without ever letting Go's user-mode scheduler run. This is the issue about it. JimB points out it causes other problems regardless of GOMAXPROCS; eventually the runtime has to stop your goroutine for garbage collection, and it can't stop for{}.
Changing for{} to select{} lets the scheduler run and doesn't eat CPU. In this reduced program, your goroutine code runs. It ends with "all goroutines are asleep - deadlock!" because your other goroutine quits and the only remaining one (main) is hung in the select{}.
package main
import "log"
const BASE_FILE_NAME = "abc_"
func mygoroutine(file_name string) {
log.Println("In goroutine for file", file_name)
}
func main() {
go mygoroutine("foo")
log.Println("Finished launching.")
select {}
log.Println("Now exiting")
}
Of course, you normally don't want to hang a goroutine even with select{}; that's going to leave some resources in use until your program ends. To build something useful you'll need something else like a sync.WaitGroup or channel.
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