[erlang-questions] Subtle behaviour of Erlang scheduler

Fri May 25 18:37:10 CEST 2007

On Fri, May 25, 2007 at 09:26:49AM -0700, Bob Ippolito wrote:
> Unless "high" means "only schedule out at synchronization points".
> It's not documented as such, but it sure could be given the behavior.
> I guess the real question is why they think they need to use it in the
> first place.

No, bob, unfortunately thing are not so. Even if high would mean 
"only schedule at synchronisation points", that does not explain 
why that piece of code DOES NOT work if executed as the first piece of
code in the erl shell, while it DOES work when executed after the 
other version (the one with explicit timer:sleep) has been executed. 

According to us, it seems to be a serious flaw in priority
management. In a couple of words: "a bug, not a feature", even if we
were not able to discover where the flaw actually is, neither looking
at the scheduler source code (erl_process.c).... :-)

The problem is not if anybody would eventually need to use a high
priority process as we do in that piece of code. The question is why
using it in that way does not produce predictable effects in case
anybody would do, as expected from a reliable and predictable
scheduler.... :-)



[ Enzo Nicosia aka KatolaZ --- GLUG Catania -- Freaknet Medialab ]
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