From: Michael Heerdegen <michael_heerdegen@web.de>
To: Noam Postavsky <npostavs@gmail.com>
Cc: 30626@debbugs.gnu.org
Subject: bug#30626: 26.0.91; Crash when traversing a `stream-of-directory-files'
Date: Wed, 28 Feb 2018 11:58:49 +0100 [thread overview]
Message-ID: <87bmg91ity.fsf@web.de> (raw)
In-Reply-To: <87lgfd52by.fsf@gmail.com> (Noam Postavsky's message of "Tue, 27 Feb 2018 20:29:21 -0500")
Noam Postavsky <npostavs@gmail.com> writes:
> >> #+begin_src emacs-lisp
> >> (seq-doseq (_ (stream-range 1 1000000)) nil)
> >> #+end_src
> >>
> >> Note that this is executed as a loop due how to streams are
> >> implemented, although the definition of `seq-doseq' looks
> >> recursive.
>
> Doesn't look recursive to me, it expands to a call to seq-do, which uses
> a simple loop.
I was imprecise, I meant that the streams are defined recursively (most
of the time). Though, it's a delayed type of recursion. Anyway, I
think that this doesn't matter here.
> > Does anyone has a reasonable idea for avoiding the crash in such
> > programs?
>
> I don't have a quick answer for the general case, but I think it's a bug
> in stream.el that it's creating such large structures in the first
> place. As far as I understand it, the point of streams is to handle
> long lists by encoding them as
>
> (FIRST-VALUE . FUNCTION-TO-PRODUCE-REST-OF-LIST)
Yes, that's exactly how it's implemented. When requesting more elements
from the stream, that becomes
(FIRST-VALUE .
(SECOND-VALUE . FUNCTION-TO-PRODUCE-MORE-REST-OF-LIST))
When we loop over the string, the cons whose car is the FIRST-VALUE,
let's call it cons1, is immediately thrown away, and we continue with
(SECOND-VALUE . FUNCTION-TO-PRODUCE-MORE-REST-OF-LIST)
etc.
AFAIU the problem is that the cons1 still exists in memory until garbage
collection kicks in. When that happens, the cons1 points to a largely
recursive cons structure, though this structure is never referenced from
Lisp in this form.
> so as to avoid allocating large amounts of memory. Is there an easy way
> to find out what the large structures are, and where they are coming
> from?
I think I've answered that. At least, I think so. What I don't
understand is that when I force the `seq-doseq' to call
`garbace-collect' explicitly every 1000 cycles, or so, it doesn't help:
the crash still happens after generating ~ 70 000 elements, or some
more, but I can't avoid the crash, no matter how often I call gc. So
I'm not sure whether these long lists are the problem or something else.
The FUNCTION-TO-PRODUCE-MORE-REST-OF-LIST looks harmless when I print
it, even after thousands of iterations, so I would not understand why
that could be problematic. streams.el implements things in a way that
these rest functions are not deeply nested lambdas.
Michael.
next prev parent reply other threads:[~2018-02-28 10:58 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-27 9:22 bug#30626: 26.0.91; Crash when traversing a `stream-of-directory-files' Michael Heerdegen
2018-02-27 11:21 ` Eli Zaretskii
2018-02-27 11:39 ` Michael Heerdegen
2018-02-27 12:08 ` Michael Heerdegen
2018-02-27 18:08 ` Eli Zaretskii
2018-02-28 1:29 ` Noam Postavsky
2018-02-28 10:58 ` Michael Heerdegen [this message]
2018-02-28 16:00 ` Eli Zaretskii
2018-02-28 16:20 ` Michael Heerdegen
2018-02-28 17:22 ` Eli Zaretskii
2018-02-28 18:25 ` Michael Heerdegen
2018-03-01 11:25 ` Michael Heerdegen
2018-03-01 15:00 ` Eli Zaretskii
2018-03-02 14:11 ` Noam Postavsky
2018-03-02 15:06 ` Michael Heerdegen
2018-03-02 15:43 ` Eli Zaretskii
2018-03-02 20:16 ` Nicolas Petton
2018-03-02 20:58 ` Nicolas Petton
2018-03-03 7:56 ` Michael Heerdegen
2018-03-03 7:54 ` Michael Heerdegen
2018-03-03 8:47 ` Nicolas Petton
2018-03-02 21:48 ` John Mastro
2018-03-03 23:00 ` Noam Postavsky
2018-03-04 15:56 ` Noam Postavsky
2018-03-04 17:02 ` Eli Zaretskii
2018-03-11 18:52 ` Noam Postavsky
2018-03-11 20:31 ` Eli Zaretskii
2018-03-11 21:51 ` Noam Postavsky
2018-03-12 3:28 ` Eli Zaretskii
2018-03-13 1:59 ` Noam Postavsky
2018-03-13 16:06 ` Eli Zaretskii
2018-03-14 0:09 ` Noam Postavsky
2018-03-15 16:34 ` Eli Zaretskii
2018-03-17 15:53 ` Noam Postavsky
2018-03-17 16:10 ` Eli Zaretskii
2018-03-17 16:27 ` Eli Zaretskii
2018-03-17 17:28 ` Noam Postavsky
2018-03-19 20:05 ` Eli Zaretskii
2019-04-25 3:20 ` Noam Postavsky
2019-04-25 5:19 ` Michael Heerdegen
2019-05-10 13:20 ` Michael Heerdegen
2019-05-25 20:29 ` Noam Postavsky
2019-05-26 0:32 ` Michael Heerdegen
2019-05-26 0:40 ` Noam Postavsky
2019-05-26 1:15 ` Michael Heerdegen
2019-06-04 0:26 ` Noam Postavsky
2018-02-28 11:05 ` Michael Heerdegen
2018-02-28 13:20 ` Nicolas Petton
2018-03-01 10:44 ` Daniel Colascione
2018-03-01 15:51 ` Noam Postavsky
2018-03-01 16:54 ` Michael Heerdegen
2018-03-01 17:15 ` Noam Postavsky
2018-03-02 7:08 ` Michael Heerdegen
2018-03-02 13:01 ` Noam Postavsky
2018-03-02 13:13 ` Michael Heerdegen
2018-03-02 13:04 ` Michael Heerdegen
2018-02-27 18:00 ` Eli Zaretskii
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