basic thread question

[birdsong]

On Aug 18, 1:10 pm, Derek Martin <c... at pizzashack.org> wrote:
> I have some simple threaded code...  If I run this
> with an arg of 1 (start one thread), it pegs one cpu, as I would
> expect.  If I run it with an arg of 2 (start 2 threads), it uses both
> CPUs, but utilization of both is less than 50%.  Can anyone explain
> why?  
>
> I do not pretend it's impeccable code, and I'm not looking for a
> critiqe of the code per se, excepting the case where what I've written
> is actually *wrong*. I hacked this together in a couple of minutes,
> with the intent of pegging my CPUs.  Performance with two threads is
> actually *worse* than with one, which is highly unintuitive.  I can
> accomplish my goal very easily with bash, but I still want to
> understand what's going on here...
>
> The OS is Linux 2.6.24, on a Ubuntu base.  Here's the code:
>
> Thanks
>
> -=-=-=-=-
>
> #!/usr/bin/python
>
> import thread, sys, time
>
> def busy(thread):
>     x=0
>     while True:
>         x+=1
>
> if __name__ == '__main__':
>     try:
>         cpus = int(sys.argv[1])
>     except ValueError:
>         cpus = 1
>     print "cpus = %d, argv[1] = %s\n" % (cpus, sys.argv[1])
>     i=0
>     thread_list = []
>     while i < cpus:
>         x = thread.start_new_thread(busy, (i,))
>         thread_list.append(x)
>         i+=1
>     while True:
>         pass
>
> --
> Derek D. Martinhttp://www.pizzashack.org/
> GPG Key ID: 0x81CFE75D
>
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watch this and all your findings will be explained: http://blip.tv/file/2232410

this talk marked a pivotal moment in my understanding of python
threads and signal handling in threaded programs.