I pointed out that maybe exec.Cmd.StdinPipe and exec.Cmd.StdoutPipe would
be better. Here’s the *modified* sample from this thread and the complete
program for easier copying to play with—no deadlock with this.
func main() { defer err2.Catch() cmdName := "/bin/bash" cmdArgs := []string{
"-c", "sleep 5"} cmd := exec.Command(cmdName, cmdArgs...) cmdStdinW :=
try.To1(cmd.StdinPipe()) cmdStdoutR := try.To1(cmd.StdoutPipe()) go func()
{ defer err2.Catch() // No need to close the pipes
try.To1(io.Copy(cmdStdinW, cmdStdoutR)) fmt.Println("copier ends") }()
try.To(cmd.Start()) // we cannot use just Run() with Cmd.XxxPipe calls...
try.To(cmd.Wait()) // ... according to docs fmt.Println("all OK") }
The entire program sample:
package main import ( "fmt" "io" "os/exec" "github.com/lainio/err2"
"github.com/lainio/err2/try" ) func main() { defer err2.Catch() cmdName :=
"/bin/bash" cmdArgs := []string{"-c", "sleep 5"} cmd :=
exec.Command(cmdName, cmdArgs...) cmdStdinW := try.To1(cmd.StdinPipe())
cmdStdoutR := try.To1(cmd.StdoutPipe()) go func() { defer err2.Catch() //
No need to close the pipes try.To1(io.Copy(cmdStdinW, cmdStdoutR))
fmt.Println("copier ends") }() try.To(cmd.Start()) // we cannot use just
Run() with Cmd.XxxPipe calls... try.To(cmd.Wait()) // ... according to docs
fmt.Println("all OK") }
On Tuesday, June 18, 2024 at 7:47:06 AM UTC+3 Ian Lance Taylor wrote:
> On Mon, Jun 17, 2024 at 7:49 PM Salvatore Domenick Desiano
> <near...@gmail.com> wrote:
> >
> > Here's a hopefully semantically identical minimal example:
> >
> > func main() {
> >
> > cmdName := "/bin/bash"
> > cmdArgs := []string{"-c", "sleep 5"}
> > cmdStdinR, cmdStdinW := io.Pipe()
> > cmdStdoutR, cmdStdoutW := io.Pipe()
> > go func() {
> >
> > defer cmdStdinW.Close()
> >
> > io.Copy(cmdStdinW, cmdStdoutR)
> >
> > }()
> > cmd := exec.Command(cmdName, cmdArgs...)
> > cmd.Stdout = cmdStdoutW
> > cmd.Stdin = cmdStdinR
> > if err := cmd.Run(); err != nil {
> >
> > fmt.Println(err)
> >
> > }
> >
> > }
> >
> > This program deadlocks after seconds. The three locked Go routines are
> the io.Copy( (stuck inside io.Copy because cmdStdoutR doesn't close), the
> exec.Command Go routine (also stuck in an io.Copy) and the main routine
> (stuck in cmd.Wait()).
>
>
> I haven't checked whether this is the problem, but as someone else
> pointed out this is a strange place to use io.Pipe. Much better to
> use os.Pipe. Much better still to use exec.Cmd.StdinPipe and
> exec.Cmd.StdoutPipe.
>
> Ian
>
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