Subject: Re: bug#21380: 25.0.50; GTK-induced segfault when scheduling timer from window-configuration-change-hook

From: Stefan Monnier <[email-masked]>
Date: Sat, 05 Sep 2015 11:18:54 -0400

> I'm not sure I understand this plan.  Are you saying that consing a
> new list in timer--activate, instead of reusing an existing cell, will
> avoid the need to wok on a copy of the timer's list when invoking the
> timer callbacks?

That's the idea, yes.

> If so, I'm probably missing something here, because
> timer--activate will update the timer list variable anyway,

This is OK: by this time, we've already read this timer list variable so
changing it won't affect us.

> doesn't it mean the value of Vtimer_list in C seen by timer_check
> changes as well that very moment?

This setq would happen after we've read the variable, so it won't affect
timer_check.

> Not to mention the fact that with timers firing every several tens of
> ms, something we've seen while discussing these bugs, allocating a
> couple of cells each time might cause a lot of consing per second,
> which in turn causes GC, which slows down everything.

How could it be worse to allocate cells when we activate a timer than
copying the whole list every time we check the timers?

        Stefan