R help - Oct 2010 - Programmaticly finding number of processors by R code

Dear List

Sorry if this question seems very basic.

Is there a function to pro grammatically find number of processors in
my system _ I want to pass this as a parameter to snow in some serial
code to parallel code functions

Regards

Ajay



Websites-
http://decisionstats.com
http://dudeofdata.com


Linkedin- www.linkedin.com/in/ajayohri

Without knowing your OS, there is no way anyone can tell you.  And you 
probably want to know 'cores' rather than CPUs. And for some specific 
OSes, you will find answers in the archives.

Beware that this is not a well-defined question: are these 
physical or virtual cores?, and having them in the system and being 
allowed to use them are different questions.

Package 'multicore' is one that attempts to do this in its function 
detectCores (see the source code).  And on Sparc Solaris it is pretty 
useless as it gives virtual CPUs, 8x the number of real CPUs.

On Sun, 3 Oct 2010, Ajay Ohri wrote:
> Dear List
>
> Sorry if this question seems very basic.
>
> Is there a function to pro grammatically find number of processors in
> my system _ I want to pass this as a parameter to snow in some serial
> code to parallel code functions
>
> Regards
>
> Ajay
>
>
>
> Websites-
> http://decisionstats.com
> http://dudeofdata.com
>
>
> Linkedin- www.linkedin.com/in/ajayohri
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
-- 
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

If no-one replies with a better way, here's a way: under
POSIX-compliant systems, you can write a small C function and wrap it
in an R function.

The C program would be something like

#include <unistd.h>
void nProcessors(int & n)
{
#ifdef _SC_NPROCESSORS_ONLN
  long nProcessorsOnline = sysconf(_SC_NPROCESSORS_ONLN);
#else
  long nProcessorsOnline = 2; // This is my guess - most computers
today have at least 2 cores
#endif
  n = (int) nProcessorsOnline;
}

You need to compile the function into a dynamic library ("shared
object" on linux) and load the dynamic library with dyn.load before
using it.

The R wrapper would be a function along the lines of

nProcessors = function()
{
   n = 0;
   res = .C("nProcessors", n = as.integer(n));
   res$n
}

I haven't actually tested the R function so please take this with a
grain of salt, but I do use the C function in my own C code. You may
also want to read this thread about potential pitfalls and
limitations, plus another (simpler) way that would work on linux:

http://forum.soft32.com/linux2/CPUs-machine-ftopict13343.html

AFAIK, this will not work on Windows because Windows is not POSIX
compliant, but I'm not sure.

Peter


On Sun, Oct 3, 2010 at 10:03 AM, Ajay Ohri <ohri2007 at gmail.com>
wrote:
> Dear List
>
> Sorry if this question seems very basic.
>
> Is there a function to pro grammatically find number of processors in
> my system _ I want to pass this as a parameter to snow in some serial
> code to parallel code functions
>
> Regards
>
> Ajay
>

In windows try this:

 Sys.getenv('NUMBER_OF_PROCESSORS')

On Sun, Oct 3, 2010 at 2:03 PM, Ajay Ohri <ohri2007@gmail.com> wrote:
> Dear List
>
> Sorry if this question seems very basic.
>
> Is there a function to pro grammatically find number of processors in
> my system _ I want to pass this as a parameter to snow in some serial
> code to parallel code functions
>
> Regards
>
> Ajay
>
>
>
> Websites-
> http://decisionstats.com
> http://dudeofdata.com
>
>
> Linkedin- www.linkedin.com/in/ajayohri
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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If you have installed multicore (for unix/mac), you can find the 
number of cores by /*multicore:::detectCores()*/

On 10/3/10 1:03 PM, Ajay Ohri wrote:
> Dear List
>
> Sorry if this question seems very basic.
>
> Is there a function to pro grammatically find number of processors in
> my system _ I want to pass this as a parameter to snow in some serial
> code to parallel code functions
>
> Regards
>
> Ajay
>
>
>
> Websites-
> http://decisionstats.com
> http://dudeofdata.com
>
>
> Linkedin- www.linkedin.com/in/ajayohri
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

-- 

Abhijit Dasgupta, PhD
Director and Principal Statistician
ARAASTAT
Ph: 301.385.3067
E: adasgupta@araastat.com
W: http://www.araastat.com


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