[cpp-threads] RE: "Agenda" for august 23-25 concurrency meeting

[Doug Lea]

Robison, Arch wrote:
> TBB's atomic operations support only relaxed consistency.  In the cited
> archive thread
> http://www.decadentplace.org.uk/pipermail/cpp-threads/2005-September/000
> 610.html, Doug Lea notes:
> 
>> And historically, almost no algorithms/programs have ever been
>> found to require such strong guarantees. We once challenged
>> people to come up with non-toy examples, and never got any.
> 
> If you have a non-toy example algorithm that shows a need for causality
> or total store order, I would very much like to see it and show it to
> our hardware architects.  
> 

Despite lack of a killer example, and my belief that macho
lock-free programmers could cope with lack of guaranteed
transitivity,  I am still uncomfortable about
relaxing requirements for TSO-ness as a both a human-factors
and language semantics concern. People seem to naturally
think causally, and will be unable to even see bugs due to
bad assumptions. So it seems like a sure thing that a relaxed
model will lead to more programming errors, especially by
less-than-expert programmers dabbling with some lock-free
constructions. Maybe hardly any of them. But of these, maybe
some really serious ones. It is not an easy decision.

-Doug