If the user has Java installed, you could execute a .class file to get
this information; for example:
public class NumProcessors {
public static void main(String[] args) {
System.out.println(Runtime.getRuntime().availableProcessors());
}
}
If you compiled this and put the resulting .class file it in the
directory of your script, you would just have to execute "java
NumProcessors" and then capture its output. This would be better than
trying to handle a different case for each OS, I think.
Elliott
On Mar 28, 2:53 pm, Ondrej Certik <ond...@certik.cz> wrote:
> Hi,
>
> I am trying to figure out the best way to automatically determine the
> number of processors and used that information to speed up Sage build.
> What is the best way of doing it?
>
> If I can assume python on the system, then one can just use:
>
> def ncpus()
> #for Linux, Unix and MacOS
> if hasattr(os, "sysconf"):
> if os.sysconf_names.has_key("SC_NPROCESSORS_ONLN"):
> #Linux and Unix
> ncpus = os.sysconf("SC_NPROCESSORS_ONLN")
> if isinstance(ncpus, int) and ncpus > 0:
> return ncpus
> else:
> #MacOS X
> return int(os.popen2("sysctl -n hw.ncpu")[1].read())
> #for Windows
> if os.environ.has_key("NUMBER_OF_PROCESSORS"):
> ncpus = int(os.environ["NUMBER_OF_PROCESSORS"])
> if ncpus > 0:
> return ncpus
> #return the default value
> return 1
>
> If Python is not available, then I can use this simple C program:
>
> http://github.com/certik/sysconf/blob/master/ncpus.c
>
> but I suspect this will not work on Mac or Windows. So if it only
> works on linux, one can just run:
>
> cat /proc/cpuinfo | grep processor | wc -l
>
> no need to compile anything.
>
> So it seems to me that a good strategy might be to write a bash script
> that will:
>
> 1) try if python is installed, if so, runs ncpus()
> 2) try to compile the above C program, if it builds, run it
> 3) if it doesn't build, we are on Mac probably, so run sysctl -n
> hw.ncpu (I don't have any Mac to test it on, but I guess there
> might be a way to actually write the C program in a portable way to
> work both on linux and Mac)
>
> Alternatively, I can change 2) to:
>
> 2) try: cat /proc/cpuinfo | grep processor | wc -l
>
> In any case, this bash script would be used only up to building
> Python. Once we have Python, we can use ncpus() from that point on.
>
> Any ideas welcome.
>
> Ondrej
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