Re: [Chicken-users] daemonize egg: redirect I/O?

[Elf]

On Fri, 26 Oct 2007, Thomas Christian Chust wrote:

> Elf wrote:
>
> > um, why not just use (duplicate-fileno (portfileno <port>))  ? [...]
>
> Because not the file descriptor of a given port should be duplicated but
> rather the file descriptor of a given port should be replaced by a
> duplicate of another one.
>
> Of course one could use (portfileno ...) instead of the fileno/...
> constants in my example, but it wouldn't make much of a difference,
> unless the ports were already set to something different from the
> standard -- but in that case it may not be such a good idea to redirect
> them. I think it makes much more sense to redirect those descriptors
> which are, by default, connected to the controlling terminal of the
> process, because they usually become useless after detaching from the
> original process group.

yes, i understood that.  hence the comment regarding the
(current-input/output/error-port) procedures being parameters that take an
argument for automatic replacement.  they need to be replaced WITH something,
though, hence the portfileno remark.

> > (re: the daemon question, i would just use
> >      (foreign-lambda int "daemon" int int) ,
> >  but thats just me.)
>
> Isn't daemon(3) a BSD C library function? I don't know whether it is
> available everywhere -- and besides that, an implementation in Scheme is
> not a lot of work but could offer a great deal of added flexibility in
> addition to what deamon(3) can do.
>
> > [...]

daemon() has been standard in libc since around 1995.  the only machines that
wont have it are windows boxen.  the direct chicken code for daemon() 
(without type or validity checking), and with an explicit continuation since
return values mean very little in this context, is:

(define (daemon nochdir noclose cnt)
    (call-with-current-continuation
        (lambda (k)
            (process-fork (lambda () (k #t)))
            (exit 0)))
    (create-session)
    (call-with-current-continuation
        (lambda (k)
            (process-fork (lambda () (k #t)))
            (exit 0)))
    (and (= 0 nochdir)
         (change-directory "/"))
    (and-let* ((cls   (= 0 noclose))
               (ipt   (open-input-file "/dev/null"))
               (opt   (open-output-file "/dev/null")))
        (current-input-port ipt)
        (current-output-port opt)
        (current-error-port opt)
        (cnt)))

the call/cc's i believe are necessary because process-fork automatically calls
(_exit 0) after evaling the lambda for the child procs.

-elf