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Re: [Chicken-users] Question again on heap mutation from signal handlers

From: Jörg F . Wittenberger
Subject: Re: [Chicken-users] Question again on heap mutation from signal handlers.
Date: 02 Oct 2011 19:02:59 +0200

On Oct 2 2011, Jörg F. Wittenberger wrote:

Kon (or maybe Felix)

On Sep 1 2011, Kon Lovett wrote:

Probably of no use to you but … When I added all the extra unix
(Chicken v2 I think) signals stuff I figured (ha) that a Scheme
signal handler could only perform operations that accessed existing
structures, no heap mutation. I used handlers that basically only
set flags.

Is there a way to verify that signal handlers can not allocate
on the heap?

As far as I understand runtime.c this should be true.
But it's fairly complicated to reason here.
It would be very, very helpful to be sure about that one.

Since my eat-all-mem issue was gone all too suddenly ...
Now I tried to re-enable the old handler invocation to confirm
that the old issue would come back.
So far it did not - which is confusing.

To summarize: no reason for confusion: "so far" meant: about 20
min. trying to force it.  Sometimes it's easier to just wait :-/

At least it reduces confusion.  A bit, that is.

If I could knew for sure that signal handlers may not touch the heap,
I would know that the approach to accept the higher latency in exchange
for the more natural coding of signal handlers would be worth the

Alan: DON'T enable the normal signal handling.  It might work some
seemingly infinite time.  But eventually goes into EAM mode.
No theory why; just observation so far.


PS: If it eventually turns out to be true that the signal handler
has been the issue I had.  Plus it would turn out to be verifiable
that always running with interrupts disabled does not eventually
harm normal behaviour.  ...  THEN I'd call that a productive time!
We could leave quite some code with the garbage collector.

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