Re: Possible Memory Leak with stream-for-each

[Andy Wingo <wingo@pobox.com>]

On Mon 19 Jul 2010 20:08, Abhijeet More <abhijeet.more@gmail.com> writes:

> 1. Can it be confirmed that this is a leak in guile's garbage
> collection?

Hi,

I can confirm this for Guile 1.9/2.0 at least. Gross... The code that I
used was, to first generate a test file:

  (with-output-to-file "/tmp/test"
    (lambda ()
      (let lp ((n 0))
        (if (< n 10000000)
            (begin
              (write '(foo))
              (lp (1+ n)))))))

Then execute the following code:

  (define stream-null? null?)
  (define the-empty-stream '())
  (define (stream-car stream) (car stream))
  (define (stream-cdr stream) (force (cdr stream)))
  (define-syntax cons-stream
    (syntax-rules ()
      ((_ ?car ?cdr) (cons ?car (delay ?cdr)))))

  (define (stream-for-each proc s)
    (if (not (stream-null? s))
        (begin (proc (stream-car s))
               (stream-for-each proc (stream-cdr s)))))

  (define (port->stream port readproc)
    (cons-stream (readproc port) (port->stream port readproc)))

  (stream-for-each
   identity
   (port->stream (open-input-file "/tmp/test") read))

And I see memory usage explode, yes, at the REPL, even if I disable
position recording via (read-disable 'positions).

> 2. Are there any workarounds (for instance doing an explicit "(gc)"
> somewhere in the definitions?
> 3. Any pointers on fixing the underlying issue?

I don't know. Ludovic? :) You have certainly found a bug, though. We
probably won't look into it for 1.8, but we will certainly try to fix it
for 2.0 (soon!).

> 4. I noticed that streams in guile (ice-9 streams) were not
> implemented in the SICP way. In-fact they were implemented in a way
> that makes recursive definitions impossible. Was this intentional?

I don't know TBH. SICP streams do have a problem, amply explored in
http://www.cs.rice.edu/~taha/publications/conference/sml98.pdf; but
beyond that, I don't know.

Perturbedly yours,

Andy
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