Re: [Chicken-hackers] [PATCH] Fix for #989 and hopefully #877 too

[Jörg F. Wittenberger]

Hi,

despite the fact that salmonella currently seems to be happy with the 
situation, let me add my €0,02.

Sometimes the solution is not more code but less.

Chicken's interrupt handling was broken for quite a long time. There is 
by now still a problem lurking and waiting to be triggered: there are 
only so many pending interrupts possible.

Let me assure you: I'm NOT making this up. This has been a problem even 
before it was introduced into chicken. RScheme happens to be very 
similar to chicken in that respect. And I've been burned by those droped 
signals before chicken received the limitation too. Please refer to the 
archives of this mailing list.

In fact I've been taught the solution to this problem when I attended 
the university. What chicken is solving when scheduling signals is 
pretty much the same problem operating system kernels solve when 
handling interrupts. We've been taught at that time that the best (in 
terms of simplicity and safety) way to handle this in a multi threaded 
environment would be to dispatch the signal/interrupt to a user level 
thread on short path. Optionally schedule this thread next for 
execution. Never handle the interrupt in the kernel itself. If you don't 
have multiple thread running (but have the machinery already, otherwise 
the point is moot) create an extra thread just for this case.

When the issue was introduced into chicken, I forked my own environment 
and just tried following the text books. Safe for some dead code I never 
had to deal with these problems again. (Let me repeat: the limited queue 
of pending interrupts was a problem in practice for me. All I have to do 
is pull the network plug when running certain code to make it visible.)

I'd love to help bringing these fixes into the mainline chicken. (After 
all it's a horrible burden to always maintain the diff). @Peter: I'm 
still waiting for your reply on that topic.

Best Regards

/Jörg

Am 05.11.2013 22:41, schrieb Mario Domenech Goulart:
> On Tue, 5 Nov 2013 16:52:16 +0100 Peter Bex <address@hidden> wrote:
>
> > The tests work, the sleep test from #989 works and the synch egg's tests
> > no longer hang, so I think this patch should probably go in ASAP.
...
> Thanks, Peter.  I could successfully run salmonella on the whole set of
> linux eggs.  I pushed your patch.
>
> Best wishes.
> Mario