[erlang-questions] : Subtle behaviour of Erlang scheduler

Corrado Santoro <>
Mon May 28 21:15:48 CEST 2007


Kenneth Lundin wrote:
> Summary:
> 
> It is important that we make clear in the documentation how priorities work and
> that you have little or no reason to use them.
> 
> I hope we can close this discussion now.
We can close the discussion, if you want, but IMHO it's quite strange to 
say, in an official documentation, that a feature is present but there's 
no reason to use it. A normal question, in this case, could be: why to 
not remove the feature, if it's useless?

In any case, I think that it's extermely rare to use Erlang for a 
CPU-bound computation like the simple code we posted. As far as I know, 
an Erlang program is made of many processes that exchange messages and 
use few CPU to process such messages. So the situation we experienced 
should never happen.

But this does not mean that, in my opinion, the Erlang priority system 
has a serious flaw and should be rethought. Probably, in a 
telecommunication system, priorities could not be so important, but if 
you use Erlang in real-time embedded environment (and it's argued that 
Erlang is for soft-real-time systems), such as automation or even 
robotics (and this is our application field), priorities are 
fundamental, together with correct or predictable behaviour of the 
scheduler.

Unless we want to exclude Erlang from some *very interesting* 
application fields....

All the best,
--Corrado

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