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

Prof Brian Ripley ripley at stats.ox.ac.uk
Fri Oct 7 21:40:39 CEST 2011

On Fri, 7 Oct 2011, Tim Triche, Jr. wrote:

> On Thu, Oct 6, 2011 at 11:25 PM, Prof Brian Ripley <ripley at stats.ox.ac.uk>
> wrote:
> Why would it make it easier?  And how could using a dummy for 'most
> users' (who are on Windows) offer them 'good parallel support'?
> Good point.  Most of my users are on unix, because my use of mclapply() is
> primarily to expedite processing of raw scanner data.  Only a handful of
> users for the packages that call mclapply() are on Windows.  Right now, I
> default to having parallel=FALSE flags all over the place, but I'd prefer
> for the default to be "go as fast as practical in the common case", i.e.,
> Unix.  It would have been more accurate for me to say "I would like to
> parallelize by default, without having the methods fail on Windows in the
> default configuration" than to claim that I want "good parallel support" for
> Windows.  When I have tried using the foreach/doMC combination in the past,
> it has not worked out satisfactorily, so I don't know how well I can support
> Windows users... period.
>       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.
> It seems similar to what I do (off topic: why do you use the file extension
> '.q' for all of the R/S code files?): pass flags around.  I suppose I was

*I* don't: the author did.  It was the recommendation for S long ago: 
.S is taken and .q stood for qpe, at one time (mind 1980s, AFAIR) the 
proposed name for 'new S'.

> just being lazy, but I would love to default to "go as fast as possible"
> without having Windows users get left out in the cold (unless they add flags
> to their function calls). 
> Thank you for your suggestions, I will look into this further.
> --
> Tim Triche, Jr.
> USC Biostatistics

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)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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