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bug#16576: Binding `standard-output' to a function doesn't work -- funct


From: Anders Lindgren
Subject: bug#16576: Binding `standard-output' to a function doesn't work -- function sometimes called with garbage
Date: Wed, 29 Jan 2014 22:12:29 +0100

Thanks for fixing the bug!

As soon as I realised that there was a problem with binding `standard-output' to a function, I rewrote the code to use a buffer instead. Also, thanks for pointing out the excessive memory usage when accumulating a string -- one can learn something new every day (even after 20 years)...

    -- Anders

Ps. I just released the package I've been working in for a couple of weeks, it's an interactive debugger for font-lock keywords. If you want to try it you can get it from https://github.com/Lindydancer/font-lock-studio



On Wed, Jan 29, 2014 at 7:01 PM, Eli Zaretskii <address@hidden> wrote:
> Date: Tue, 28 Jan 2014 23:00:32 +0100
> From: Anders Lindgren <address@hidden>
> Cc: address@hidden
>
> Well, the main issue here is if this is a real bug or not. You originally
> thought this was simply a mistake in the example I provided -- do you still
> think so?

There was indeed a bug, now fixed on the trunk, which caused the
problem.  It was a very old bug, it went unnoticed until now because,
I guess, no one conses a string one character at a time -- this is a
terrible idea in Emacs Lisp.  Use a temporary buffer instead.

There was nothing wrong with prin1 per se, btw, it's just that its
subroutine which prints a string wasn't safe when GC hit in the middle
of a prin1 call.  The code protected the string from GC, but that
doesn't preclude relocation of string data, so holding to C 'char *'
pointers is not safe in these situations.  And printing a
800-character string like you did triggers GC every time, because it
creates 800 string objects for a grand total of about 320000 bytes.

Anyway, problem solved, and I'm closing the bug.  Thanks.


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