Re: [Chicken-users] Possible stack problem with fork

[felix winkelmann]

On Wed, 02 Feb 2005 23:19:36 +0100, Peter Bex <address@hidden> wrote:
> Hi all,
> 
> I've encountered a really strange bug, and I'm wondering if it's my
> own mistake or there's a bug somewhere in chicken.
> 
> The code I have is this:
> 
> (define (run-and-catch-output program args)
>   (call-with-values
>     create-pipe
>     (lambda (in out)
>       (let* ([child (lambda ()
>                       (file-close in)                           ; Close read 
> end
>                       (duplicate-fileno out fileno/stdout)      ; out = stdout
>                       (process-execute program args))]
>              [child-pid (process-fork child)])
>         (file-close out)                        ; Close write end
>         (let ([str (read-string in)])           ; Read out entire file as 
> string
>           (process-wait child-pid)              ; Clean up zombie
>           str) )) ))                            ; Return string

- you didn't pass the length indicator to read-string (the first argument)
- read-string only works for ports, not file-descriptors, use file-read
  instead.
- process-wait returns multiple values, this triggers the error, since
  it is not called in a multiple values context [1]

> 
> 
> Note the second error message.  Somehow the string "display" is getting
> mangled.
> 

I'm not sure about this, perhaps due to the error the I/O gets somehow
mixed up.

I will add a second optional parameter to `process' that can be
used to specify a list of arguments and which will invoke the program
directly (not via the shell) - `process' is much easier to use than
doing everything by hand (I would check this in, but I'm currently
behind a firewall).

[1] this is R5RS compliant, but at the same time sometimes a bit
inconvenient - I'm thinking about relaxing this a little (allowing
returning multiple values in a single value context). It could be
implemented by returning only the first value (or void, if zero
values are returned). 


cheers,
felix