bug#15228: making open-process public [Was: Re: Using open-input-output-pipe]

bug#15228: making open-process public [Was: Re: Using open-input-output-pipe]

[Amirouche Boubekki]

Moving the conversation to guile-devel.

Can I have feedback on the patch I sent for #15228

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=15228

On 2018-01-22 16:40, Edwin Watkeys wrote:
> Hi all,
> 
> Thanks for all the input. Here a simple implementation that I've come 
> up
> with; I'm not sure it's bullet-proof. This scenario is so common—using
> open-input-output-port on a Unix filter—that I would argue that the 
> rw-port
> design is broken; there really should be a way to close the input and
> output independently. I checked back on the mailing list to the genesis 
> of
> this feature, and there didn't seem to be a lot of discussion of the
> design. Something that's analogous to open-process, which returns 
> multiple
> values, or a hypothetical (call-with-port-input-output ARGS (lambda (in
> out) ...)) would seem to be better. I'm going to try out these ideas 
> when I
> get a bit of spare time.
> 
> (define (generate-digest str)
>   (call-with-values
>       (lambda () (open-process OPEN_BOTH "shasum" "-a" "256"))
>     (lambda (read-port write-port pid)
>       (write str write-port)
>       (close-port write-port)
>       (let ((line (read-line read-port)))
> (close-port read-port)
> (car (string-split line #\space))))))
> 
> Regards,
> Edwin
> 
> On Mon, Jan 22, 2018 at 6:00 AM, Chris Vine <vine35792468@gmail.com> 
> wrote:
> 
>> > On 01/21/2018 12:31 PM, Edwin Watkeys wrote:
>> >
>> > > Hi all,
>> > >
>> > > I'm trying to write a procedure that processes some input through a
>> > > unix utility. Open-input-output-pipe returns a bidirectional pipe
>> > > that I can both read and write to. However, there is no way that I
>> > > can figure out to tell the external process that input is complete,
>> > > as there is no way to determine the output port of the rw-port and
>> > > therefore no way to close it. Closing an rw-port closes both the
>> > > read and write ports.
>> > >
>> > > Open-input-output-port therefore seems useful for line-based
>> > > external processes but not for ones that function on the entirety
>> > > of user input e.g. wc and sort.
>> > >
>> > > Is my analysis of the situation roughly accurate?
>> > >
>> > > Regards,
>> > > Edwin
>> 
>> If you want fine-grained control, you might want to look at some of 
>> the
>> procedures in guile-lib's (os process) module, and in particular the
>> 'run-with-pipe' procedure, or using its 'run-concurrently+' procedure
>> with guile's 'pipe' (the parent can block on its read pipe once it has
>> completed writing to the child until the child process closes the 
>> other
>> end of the pipe upon finishing, causing the parent to get an 
>> eof-object
>> provided it has itself previously closed the write end of its read
>> pipe).
>> 
>> Otherwise if you want to stick to guile proper, you may have to do it 
>> by
>> hand.  As 'pipe' gives you an input and output port for each pipe 
>> which
>> can be independently closed, you could use two of these with the
>> 'dup2', 'fork' and 'execl' procedures.  It's tedious though.
>> 
>> Chris
>> 
>> 

-- 
Amirouche ~ amz3 ~ http://www.hyperdev.fr