https://github.com/golang/go/blob/master/src/os/exec/exec.go#L484 set
io.Writer explicitly so it looks like a bug
среда, 13 июля 2016 г., 23:50:56 UTC+3 пользователь noxiouz написал:
>
> Good day!
>
> I faced a corner case of cmd.Exec usage and want to find out if it's
> designed behavior.
>
>
> go version go1.6.2 darwin/amd64 and linux
>>
>
> Let's assume we use cmd.Exec to start some process, that can fork and
> dies, but the fork will live forever. For example:
>
> #!/usr/bin/env python
>
> import os
> import time
>
> pid = os.fork()
> if pid == 0:
> while True:
> time.sleep(10)
>
> print "main process has quited"
>
>
> The real script is much more complicated but it's not important.
>
> Also there is a go code:
>
> package main
>
> import (
> "io"
> "log"
> "os/exec"
> )
>
> func main() {
> cmd := exec.Command("./forker.py")
> rd, wr := io.Pipe()
> cmd.Stdout = wr
> go func() {
> b := make([]byte, 100)
> for {
> nn, err := rd.Read(b)
> if nn > 0 {
> log.Printf("%s", b[:nn])
> }
> if err != nil {
> log.Fatal(err)
> return
> }
> }
> }()
> if err := cmd.Start(); err != nil {
> log.Fatal(err)
> }
>
> log.Printf("PID %d", cmd.Process.Pid)
>
> if err := cmd.Wait(); err != nil {
> log.Fatal(err)
> }
> }
>
> The output would be like this:
>
> 2016/07/13 23:40:20 PID 90614
>> 2016/07/13 23:40:20 main process has quited
>>
>
> but the Go process will hang forever, because of waiting on:
> https://github.com/golang/go/blob/release-branch.go1.6/src/os/exec/exec.go#L401
> I think, because stdout fd of child process would not be closed .
>
> On the other hand the next code works perfectly and does not hang:
>
> package main
>
> import (
> "log"
> "os/exec"
> )
>
> func main() {
> cmd := exec.Command("./forker.py")
> rd, err := cmd.StdoutPipe()
> if err != nil {
> log.Fatal(err)
> }
> go func() {
> b := make([]byte, 100)
> for {
> nn, err := rd.Read(b)
> if nn > 0 {
> log.Printf("%s", b[:nn])
> }
> if err != nil {
> log.Fatal(err)
> return
> }
> }
> }()
> if err := cmd.Start(); err != nil {
> log.Fatal(err)
> }
>
> log.Printf("PID %d", cmd.Process.Pid)
>
> if err := cmd.Wait(); err != nil {
> log.Fatal(err)
> }
> }
>
>
> So I would like to find out if setting cmd.Stdout explicitly is not
> expected.
>
>
> Thanks!
>
>
>
>
>
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