(j3.2006) (SC22WG5.4109) [ukfortran] Standard intrinsics and coarrays

[Bill Long]

N.M. Maclaren wrote:

> 
>     Systems with suitable compare-and-swap hardware can implement
> parallel use of a shared RANDOM_NUMBER safely without locking.  Adding
> RANDOM_SEED to the mix makes that much trickier, and it's not something
> that any sane programmer would do, anyway.
> 

As a (my) performance rule of thumb, if you can generate 1.e9 64-bit 
values per second you are OK. In some cases, 1.e8 might be considered. 
Even with hardware compare-and-swap, a shared generator on an even 
modest sized system will have trouble with this. The scheme has no 
chance of scaling to large numbers of images.  And it still fails the 
reproducibility requirement.

Cheers,
Bill


-- 
Bill Long                                   longb at cray.com
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