[Chicago] threading is slow

[Alex MacKay]

Has anyone used Python threads to make a sweater?

On Mar 6, 2013, at 5:19 PM, Brantley Harris wrote:

> Whoa, back up.  What are you trying to do with threads?
> 
> 
> On Wed, Mar 6, 2013 at 5:05 PM, Daniel Griffin <dgriff1 at gmail.com> wrote:
> Python has a GIL so threads mostly sort of suck. Use multiprocessing, twisted or celery.  
> 
> 
> On Wed, Mar 6, 2013 at 3:29 PM, Oren Livne <livne at uchicago.edu> wrote:
> Dear All,
> 
> I am new to python multithreading. It seems that using threading causes a slow down with more threads rather than a speedup. should I be using the multiprocessing module instead? Any good examples for threads reading from a queue with multiprocessing?
> 
> Thanks so much,
> Oren
> 
> #!/usr/bin/env python
> '''Sum up the first 100000000 numbers. Time the speed-up of using multithreading.'''
> import threading, time, numpy as np
> 
> class SumThread(threading.Thread):
>     def __init__(self, a, b):
>         threading.Thread.__init__(self)
>         self.a = a
>         self.b = b
>         self.s = 0
> 
>     def run(self):
>         self.s = sum(i for i in xrange(self.a, self.b))
> 
> def main(num_threads):
>     start = time.time()
>     a = map(int, np.core.function_base.linspace(0, 100000000, num_threads + 1, True))
>     # spawn a pool of threads, and pass them queue instance
>     threads = []
>     for i in xrange(num_threads):
>         t = SumThread(a[i], a[i + 1])
>         t.setDaemon(True)
>         t.start()
>         threads.append(t)
> 
>     # Wait for all threads to complete
>     for t in threads:
>         t.join()
> 
>     # Fetch results
>     s = sum(t.s for t in threads)
>     print '#threads = %d, result = %10d, elapsed Time: %s' % (num_threads, s, time.time() - start)
> 
> for n in 2 ** np.arange(4):
>     main(n)
> 
> Output:
> #threads = 1, result = 4999999950000000, elapsed Time: 12.3320000172
> #threads = 2, result = 4999999950000000, elapsed Time: 16.5600001812  ???
> #threads = 4, result = 4999999950000000, elapsed Time: 16.7489998341  ???
> #threads = 8, result = 4999999950000000, elapsed Time: 16.6720001698  ???
> 
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