If your forked process still has stdin / stdout open then I would say
this is expected.
You could confirm this by adding the following to the python script.
import sys
...
if pid == 0:
sys.stdin.close()
sys.stdout.close()
On 13/07/2016 21:50, noxiouz wrote:
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
importos
importtime
pid =os.fork()
ifpid ==0:
whileTrue:
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:
|
packagemain
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)
ifnn >0{
log.Printf("%s",b[:nn])
}
iferr !=nil{
log.Fatal(err)
return
}
}
}()
iferr :=cmd.Start();err !=nil{
log.Fatal(err)
}
log.Printf("PID %d",cmd.Process.Pid)
iferr :=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:
|
packagemain
import(
"log"
"os/exec"
)
func main(){
cmd :=exec.Command("./forker.py")
rd,err :=cmd.StdoutPipe()
iferr !=nil{
log.Fatal(err)
}
go func(){
b :=make([]byte,100)
for{
nn,err :=rd.Read(b)
ifnn >0{
log.Printf("%s",b[:nn])
}
iferr !=nil{
log.Fatal(err)
return
}
}
}()
iferr :=cmd.Start();err !=nil{
log.Fatal(err)
}
log.Printf("PID %d",cmd.Process.Pid)
iferr :=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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