[Caml-list] Child process doesn't terminate

[Caml-list] Child process doesn't terminate

[Johan Grande]

Hi,

In the following program, the child process "cat" never terminates. I 
don't understand why; can anyone tell me?

~~~
let _ =
   let open Unix in
   let indescr, outdescr = pipe () in
   let outchan = out_channel_of_descr outdescr in
   let pid =
     create_process "/bin/cat" [|"cat"|]
       indescr  stdout  stderr
   in
   Printf.fprintf outchan "Hello!\n%!";
   close indescr;
   close outdescr;
   ignore (waitpid [] pid)  (* stuck here *)
~~~

-- 
Johan Grande

Re: [Caml-list] Child process doesn't terminate

[Gerd Stolpmann]

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Am Montag, den 24.03.2014, 19:23 +0100 schrieb Johan Grande:
> Hi,
> 
> In the following program, the child process "cat" never terminates. I 
> don't understand why; can anyone tell me?

Because outdescr isn't closed in the child. Set the close-on-exec flag
on it.

Gerd


> ~~~
> let _ =
>    let open Unix in
>    let indescr, outdescr = pipe () in
>    let outchan = out_channel_of_descr outdescr in
>    let pid =
>      create_process "/bin/cat" [|"cat"|]
>        indescr  stdout  stderr
>    in
>    Printf.fprintf outchan "Hello!\n%!";
>    close indescr;
>    close outdescr;
>    ignore (waitpid [] pid)  (* stuck here *)
> ~~~
> 
> -- 
> Johan Grande
> 

-- 
------------------------------------------------------------
Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
My OCaml site:          http://www.camlcity.org
Contact details:        http://www.camlcity.org/contact.html
Company homepage:       http://www.gerd-stolpmann.de
------------------------------------------------------------

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Re: [Caml-list] Child process doesn't terminate

[oliver]

Hello,

On Mon, Mar 24, 2014 at 07:23:05PM +0100, Johan Grande wrote:
> Hi,
> 
> In the following program, the child process "cat" never terminates.
> I don't understand why; can anyone tell me?
> 
> ~~~
> let _ =
>   let open Unix in
>   let indescr, outdescr = pipe () in
>   let outchan = out_channel_of_descr outdescr in
>   let pid =
>     create_process "/bin/cat" [|"cat"|]
>       indescr  stdout  stderr
>   in
>   Printf.fprintf outchan "Hello!\n%!";
>   close indescr;
>   close outdescr;
>   ignore (waitpid [] pid)  (* stuck here *)
> ~~~


"cat" does not terminate.


With

  create_process "/bin/cat" [| "cat"; "/etc/passwd" |]

cat would terminate after cat'ing the file,
otherwise it reads from input until Ctrl-D arrives,
before printing the data and then terminates.

So you can wait in vain with your waitpid-call,
if you call it as you did.


Ciao,
   Oliver

Re: [Caml-list] Child process doesn't terminate

[Johan Grande]

Le 24/03/2014 22:28, Gerd Stolpmann a écrit :
> Am Montag, den 24.03.2014, 19:23 +0100 schrieb Johan Grande:
>> In the following program, the child process "cat" never terminates. I
>> don't understand why; can anyone tell me?
>
> Because outdescr isn't closed in the child. Set the close-on-exec flag
> on it.

Indeed, set_close_on_exec did the trick. Thanks!

-- 
Johan

Re: [Caml-list] Child process doesn't terminate

[Johan Grande]

Le 24/03/2014 23:55, oliver a écrit :
> On Mon, Mar 24, 2014 at 07:23:05PM +0100, Johan Grande wrote:
>> In the following program, the child process "cat" never terminates.
>> I don't understand why; can anyone tell me?
>>
>> [...]
>
> With
>
>    create_process "/bin/cat" [| "cat"; "/etc/passwd" |]
>
> cat would terminate after cat'ing the file,
> otherwise it reads from input until Ctrl-D arrives,
> before printing the data and then terminates.

Yes, but if I'm not mistaken I can't just send Ctrl+D to the process. 
The equivalent here is to close the channel; Gerd pointed out how to do 
this properly.

-- 
Johan