[gambit-list] detecting closed ports

Dimitris Vyzovitis vyzo at hackzen.org
Sat Mar 24 07:59:51 EDT 2018


that's a very good point, i keep forgetting about the non-permanent closure
of pipes and its usability.
snarfing the read/write stage from the device may be ok, although we won't
be able to tell for pure scheme ports.

-- vyzo

On Sat, Mar 24, 2018 at 1:56 PM, Marc Feeley <feeley at iro.umontreal.ca>
wrote:

> Knowing that close-port was called on a port is not sufficient to tell if
> the port is “closed” or not.  Apart from what it means for a port to be
> “closed”, there are ports that don’t close permanently when close-port is
> called on them.  See the example below of a pipe used for the communication
> between two threads.  It allows using close-port to send an “end-of-file”
> to the other thread multiple times.
>
> For “device” ports however, there is a state in the port object at the C
> level.  The fields read_stage and write_stage will be different from
> ___STAGE_OPEN when the device port no longer accepts reading or writing.
> Perhaps that is the information you want.  Note that not all ports are
> device ports.
>
> Marc
>
>
> (define in #f)
> (define out #f)
>
> (receive (i o) (open-string-pipe (list permanent-close: #f))
>   (set! in i)
>   (set! out o))
>
> (define (send x)
>   (write x out)
>   (newline out)
>   (force-output out)
>   (thread-sleep! 0.5))
>
> (define (close)
>   (close-output-port out)
>   (thread-sleep! 0.5))
>
> (thread-start!
>  (make-thread
>   (lambda ()
>     (let loop ()
>       (let ((x (read in)))
>         (pp x)
>         (loop))))))
>
> (send '(11))
> (send '(22))
>
> (close)
>
> (send '(33))
> (send '(44))
>
> (close)
> (close)
>
> (send '(55))
>
> ;; output:
> ;; (11)
> ;; (22)
> ;; #!eof
> ;; (33)
> ;; (44)
> ;; #!eof
> ;; #!eof
> ;; (55)
>
>
> > On Mar 24, 2018, at 5:51 AM, Dimitris Vyzovitis <vyzo at hackzen.org>
> wrote:
> >
> > You can't tell if a file descriptor is closed in general, that's not
> what I am after.
> > I just want to know if close-port was applied to the port.
> >
> > -- vyzo
> >
> > On Sat, Mar 24, 2018 at 11:43 AM, Adam <adam.mlmb at gmail.com> wrote:
> > The BSD/unix API does not allow this for TCP sockets, as in tapping into
> the OS' knowledge of whether a connection was closed, the only way to learn
> that is by trying to write to it.
> >
> > However with respect to Gambit knowing whether |close-port| was applied
> on a port, of course you should be able to retrieve that.
> >
> > 2018-03-24 16:29 GMT+08:00 Dimitris Vyzovitis <vyzo at hackzen.org>:
> > Is there a reasonable way to detect whether a port has been closed?
> > I want to implement input-port-open? and output-port-open? for r7rs
> coverage...
> >
> > -- vyzo
> >
> > _______________________________________________
> > Gambit-list mailing list
> > Gambit-list at iro.umontreal.ca
> > https://webmail.iro.umontreal.ca/mailman/listinfo/gambit-list
> >
> >
> >
>
>
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