[Rd] parallel::mclapply() dummy function on Windows?

[Prof Brian Ripley]

On Thu, 6 Oct 2011, Tim Triche, Jr. wrote:

> Hi all,
>
> Would it be possible to have the new 'parallel' library export a dummy
> function, something akin to
>
> if(Windows) mclapply <- lapply
>
> to paper over the lack of fork() support on said platform?  This may not be
> the world's greatest idea, but it would make it easier for me to maintain my
> package and still offer most users good parallel support.  Plus, I can't

Why would it make it easier?  And how could using a dummy for 'most 
users' (who are on Windows) offer them 'good parallel support'?

> really see where it would cause problems, but then I don't develop R,
> myself.

Take a look at e.g. package 'boot' to see how to offer alternatives. 
(A version that uses 'parallel' is pending on CRAN, or see 
http://www.stats.ox.ac.uk/pub/R/boot_1.3-3.tar.gz .) Package 
'parallel' may in future offer a higher-level abstraction layer that 
makes offers such a choice, but as the 'boot' code shows, deciding 
what to send to the workers in a snow-style cluster is not simple.

Note that it is not just Windows that lacks fork support: some 
front-ends (notably Rstudio) do not work with forking at present. And 
some parts of parallel (and multicore/snow) do not work reliably on 
some OSes (e.g. Solaris).

> Thanks for any thoughts on the matter.
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
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