python threads?

[Stephen Adler]

Hi all you pynuts...

I'm playing around with the threading module and wrote a simple test to 
see python threads in action. The supprize was that it was easy to 
implement, but I didn't get the full mult-thread benefit that I thought 
I would get.
Basically, I have a counter object which counts up private instance of 
an integer. I then spawn N number of these threads, expecting the real 
time execution to be constant up to the number of CPU's on my system. 
What I found out was that spawning 1 thread, I use up 99% of a CPU, if I 
spawn 2 threads, I get 115%, (i.e. 1 whole CPU and 15% of another.) 
Spawning 3 threads, I get 115%.... So I'm wondering why the python 
thread does not use up two full CPU's? My code, and some time commands 
follow...

#!/usr/bin/env python
# Copyright (c) GPL.

# This code prototypes the use of threads in python

import threading
import optparse
import sys

class Counter(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        self._counter=0
    def run(self):
        while 1:
            self._counter+=1
            #if (self._counter%1000000 == 0):
             #   print self._counter
            if (self._counter==10000000):
                return

if __name__ == '__main__':
    print 'pythread test'
    print sys.argv
    nbOfThreads=int(sys.argv[1])
    ThreadList=[];
    for i in range(nbOfThreads):
        ThreadList.append(Counter())
        ThreadList[i].start()

    for i in range(nbOfThreads):
        ThreadList[i].join()

[adler at telacode pythreads]$ time ./pythread.py 1
pythread test
['./pythread.py', '1']

real    0m5.584s
user    0m5.398s
sys     0m0.159s
[adler at telacode pythreads]$ time ./pythread.py 2
pythread test
['./pythread.py', '2']

real    0m13.481s
user    0m12.290s
sys     0m2.951s
[adler at telacode pythreads]$ time ./pythread.py 3
pythread test
['./pythread.py', '3']

real    0m19.648s
user    0m17.757s
sys     0m4.899s


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