bug#29463: 27.0.50; Backtraces with large strings is very slow

bug#29463: 27.0.50; Backtraces with large strings is very slow

[Lars Ingebrigtsen]

I was trying to debug some code that dealt with very large SVG images,
and getting a backtrace buffer proved impossible -- Emacs would just
hang.

Here's a trivial test case:

(let ((a (make-string 100000000 ?a)))
 (debug a))

On my machine, this takes about half a minute to display, but if you
have deeply nested code that the debugger is trying to display, you'll
get that additional time per frame, I think, so it can take arbitrarily
long to render the buffer.

It would be nice if the backtrace buffer would just chop off
ridiculously long strings instead of printing them.  Perhaps controlled
by a -print-length variable?


In GNU Emacs 27.0.50 (build 4, x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
 of 2017-10-26 built on stories
Repository revision: 1ad56d0a6bdd07c722a3c161096a16f70d1cbb35
Windowing system distributor 'The X.Org Foundation', version 11.0.11902000
System Description:	Debian GNU/Linux 9.2 (stretch)


-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#29463: Backtraces with large strings is very slow

[Kaushal Modi]

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> I was trying to debug some code that dealt with very large SVG images,
and getting a backtrace buffer proved impossible -- Emacs would just
hang.

+1. Though I see that slow-down on backtrace on emacs-26 branch too..
especially when edebugging/debugging through code in an Org exporter.

Org exporters use an INFO plist that contains loads of information for the
whole Org buffer (which is common to be 1000's of lines). So each time the
edebug step comes to the info variable, it could few minutes for emacs
before I can move on to the next edebug step.
-- 

Kaushal Modi

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bug#29463: Backtraces with large strings is very slow

[Noam Postavsky]

merge 29463 18558
quit

Kaushal Modi <kaushal.modi@gmail.com> writes:

>> I was trying to debug some code that dealt with very large SVG
> images,
> and getting a backtrace buffer proved impossible -- Emacs would just
> hang.
>
> +1. Though I see that slow-down on backtrace on emacs-26 branch too..
> especially when edebugging/debugging through code in an Org exporter.

It's been reported as far back as 24.4.

bug#29463: 27.0.50; Backtraces with large strings is very slow

[Lars Ingebrigtsen]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> I was trying to debug some code that dealt with very large SVG images,
> and getting a backtrace buffer proved impossible -- Emacs would just
> hang.
>
> Here's a trivial test case:
>
> (let ((a (make-string 100000000 ?a)))
>  (debug a))
>
> On my machine, this takes about half a minute to display, but if you
> have deeply nested code that the debugger is trying to display, you'll
> get that additional time per frame, I think, so it can take arbitrarily
> long to render the buffer.

This has been fixed in Emacs 27 by shortening the display of the
strings, so I'm closing this bug report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no