[Caml-list] Unix.wait: strange behavior

[Caml-list] Unix.wait: strange behavior

[Yang Shouxun]

Hi,

I'm reading ocaml-book English version. On p. 611:
----8<----
match Unix.fork () with
     0 -> Printf.printf "fair Marquise " ; flush stdout
   | _  -> ignore (Unix.wait ()) ;
           match Unix.fork () with
               0 -> Printf.printf "your beautiful eyes " ; flush stdout
             | _ -> ignore (Unix.wait ()) ;
                   match Unix.fork () with
                       0 -> Printf.printf "make me die " ; flush stdout
                     | _ -> ignore (Unix.wait ()) ;
                    Printf.printf "of love\n" ;
                    flush stdout
----8<----
this is intended to show the use of Unix.wait to wait for the 
termination of the child.

Strangely, when I input at the Ocaml toplevel, it does not print "fair 
Marquise your beautiful eyes make me die of love", but only "fair 
Marquise". The forked processes did not terminate for some reason, which 
I don't understand why. Is this a bug?

Guessing that the child processes will not automatically exit, I added 
"; exit 0" to the lines for newly forked processes, and I got "your 
beautiful eyes make me die of love" printed before the return of the 
expression and then "fair Marquise " printed.

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Re: [Caml-list] Unix.wait: strange behavior

[Remi VANICAT]

Yang Shouxun <yangsx@fltrp.com> writes:

> Hi,
>
> I'm reading ocaml-book English version. On p. 611:
> ----8<----
> match Unix.fork () with
>      0 -> Printf.printf "fair Marquise " ; flush stdout
>    | _  -> ignore (Unix.wait ()) ;
>            match Unix.fork () with
>                0 -> Printf.printf "your beautiful eyes " ; flush stdout
>              | _ -> ignore (Unix.wait ()) ;
>                    match Unix.fork () with
>                        0 -> Printf.printf "make me die " ; flush stdout
>                      | _ -> ignore (Unix.wait ()) ;
>                     Printf.printf "of love\n" ;
>                     flush stdout
> ----8<----
> this is intended to show the use of Unix.wait to wait for the
> termination of the child.
>
> Strangely, when I input at the Ocaml toplevel, it does not print "fair
> Marquise your beautiful eyes make me die of love", but only "fair
> Marquise". The forked processes did not terminate for some reason,
> which I don't understand why. Is this a bug?

Mmm, Don't know if this a bug or not, but the problem is that after
forking, you have two toplevel, so personally I've something like :

# match Unix.fork () with
       0 -> Printf.printf "fair Marquise " ; flush stdout
[....]
fair Marquise - : unit = ()
# #quit
  ;;
your beautiful eyes - : unit = ()
# #quit ;;
make me die - : unit = ()
# #quit ;;
of love
- : unit = ()
# 


>
> Guessing that the child processes will not automatically exit, I added
> "; exit 0" to the lines for newly forked processes, and I got "your
> beautiful eyes make me die of love" printed before the return of the
> expression and then "fair Marquise " printed.

Strange, I've the waited output.
-- 
Rémi Vanicat
vanicat@labri.u-bordeaux.fr
http://dept-info.labri.u-bordeaux.fr/~vanicat
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Re: [Caml-list] Unix.wait: strange behavior

[Yang Shouxun]

As a follow-up to my initial post, I found that the strange behavior is 
due to the difference of toplevel and byte-compiled. The code, when 
byte-compiled, will act as described in the book. When run at the 
interactive toplevel, acts as I reported.

That's a good lesson for me that there are big differences between the 
three different modes.

Yang Shouxun wrote:
> Hi,
> 
> I'm reading ocaml-book English version. On p. 611:
> ----8<----
> match Unix.fork () with
>     0 -> Printf.printf "fair Marquise " ; flush stdout
>   | _  -> ignore (Unix.wait ()) ;
>           match Unix.fork () with
>               0 -> Printf.printf "your beautiful eyes " ; flush stdout
>             | _ -> ignore (Unix.wait ()) ;
>                   match Unix.fork () with
>                       0 -> Printf.printf "make me die " ; flush stdout
>                     | _ -> ignore (Unix.wait ()) ;
>                    Printf.printf "of love\n" ;
>                    flush stdout
> ----8<----
> this is intended to show the use of Unix.wait to wait for the 
> termination of the child.
> 
> Strangely, when I input at the Ocaml toplevel, it does not print "fair 
> Marquise your beautiful eyes make me die of love", but only "fair 
> Marquise". The forked processes did not terminate for some reason, which 
> I don't understand why. Is this a bug?
> 
> Guessing that the child processes will not automatically exit, I added 
> "; exit 0" to the lines for newly forked processes, and I got "your 
> beautiful eyes make me die of love" printed before the return of the 
> expression and then "fair Marquise " printed.

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