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Re: sit-for

From: David Kastrup
Subject: Re: sit-for
Date: Sat, 29 Jul 2006 10:40:20 +0200
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.0.50 (gnu/linux)

David Kastrup <address@hidden> writes:

> Chong Yidong <address@hidden> writes:
>> David Kastrup <address@hidden> writes:
>>> Since we have the new sit-for implementation, I have a lot of times
>>> when Emacs just pauses in busy waiting for input.  This happens
>>> spontaneously.  One situation where it happens frequently is when
>>> reading news with gnus.
>> I haven't seen this problem in my usage of gnus.
> It is not just gnus.  And it is not easy to see: Emacs gets somewhat
> sluggish, sometimes the cursor blinks quite less than expected, and
> CPU usage goes up, up, up, which is of course mostly noticeable when
> you have power management, and the fans start waking up.
>> It would be helpful if you could be more specific: does the problem
>> happen with the 2006-07-26 change to `read-event'?
> Already before.  I have now recompiled Emacs and will see whether this
> changes something.

Update: it still happens.  I am working for a while in a web browser,
suddenly the fans engage, the Emacs frame (not even mapped when this
happens) shows a very slow and erratically blinking cursor, and `top'
shows that Emacs is consuming close to 100% of CPU power.

So yes, even an off-screen Emacs sitting idle in some frame suddenly
decides to suck up all CPU power.

>> If so, did it start to happen at that time, or did it already
>> happen after the Lisp-level `sit-for' was implemented?
>> If it only started after the `read-event' change, one possibility
>> is that read_char is getting stuck somewhere before we get to the
>> point where we check if the timeout has elapsed.
>>> This is really a nuisance.  The change to sit-for is a fundamental
>>> change to some core mechanism of Emacs, and it is currently
>>> seemingly breaking quite a few things, apart from causing strange
>>> effects.
>> That's the story of the Emacs 22 feature freeze.

I can't remember any change as invasive as that without a
correspondingly bad bug it was trying to fix.

David Kastrup, Kriemhildstr. 15, 44793 Bochum

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