Re: Some introductory docs about C level threading

[Marius Vollmer <marius.vollmer@uni-dortmund.de>]

Ken Raeburn <raeburn@raeburn.org> writes:

>> SCM type will mean it's atomic.
>
> If use of the SCM type is assumed to be atomic in terms of CPU memory
> access and inter-CPU memory consistency, that's fine, but it should be
> documented as such -- and we should acknowledge that ports to
> architectures where that assumption does not hold may not be possible.

Yes, this is exactly my intention.

> [...]
> Depending on just how it works out, that could mean essentially
> declaring some of the scheme object types (like cons cells) as
> volatile, which would be poor for performance.

That would be no show-stopper: if Guile can only be correct with poor
performance on some platform, than we have to swallow that.

> And volatile declarations may fix the possibility of storing
> incomplete values, but I don't think it would deal with the
> cross-thread memory access ordering issue.

As long as accesses to SCM values are atomic, the ordering of
loads/stores across threads can be arbitrary.


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