[plt-scheme] Process hangs with big input

From: Robby Findler (robby at cs.uchicago.edu)
Date: Tue Mar 14 09:33:12 EST 2006

Yes, the ports created by process are buffered. 

If you have a lot of output and can do something with it as it comes
(rather than waiting until it all shows up), it is probably better to
just work directly with the ports, rather than waiting for the process
to finish and creating intermediate strings. The combination of our
new(ish) ports library and CML-style message passing concurrency makes
this easy to do and it scales to lots of data.

If, however, you really want the output in a string, create a pipe and
a thread. Have the thread copy the out and/or err to one side of the
pipe and get a string from the other side of the pipe (don't forget to
have the thread close the ports when it is done copying). Pipes can be
created with an internal buffer that is unbounded.

What are you doing, in this particular case?


At Tue, 14 Mar 2006 06:23:54 -0800 (PST), Noel Welsh wrote:
> Hi all,
> I'm trying to control an external process (svn) using the
> process function in (lib "process.ss")  I want to capture
> the output so I've wrapped process in this fucntion from
> the Scheme Cookbook:
>   (define (system/output command-string)
>     (let-values (((out in id err ctrl)
>                   (apply values (process command-string))))
>       (ctrl 'wait)  ;; wait for the process to finish
>       (begin0
>           (case (ctrl 'status)
>             ((done-ok)
>              (port->string out))
>             (else #f))
>         (close-output-port in)
>         (close-input-port out)
>         (close-input-port err))))
> When the process creates a small amount of output
> system/output terminates.  When the process creates a large
> amount of output it never terminates.  Debugging by hand I
> always get:
> > (ctrl 'status)
> running
> Could there be a buffer that fills up, preventing the
> process from writing my output and terminating.  Looking
> through process.ss has not shed much light.
> Thanks,
> Noel
> Email: noelwelsh <at> yahoo <dot> com   noel <at> untyped <dot> com
> AIM: noelhwelsh
> Blogs: http://monospaced.blogspot.com/  http://www.untyped.com/untyping/
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