Multi-threaded map() for Python2007-09-05 at 04:39 | Posted in devel, lang:en, talk | 13 Comments
Tags: concurrency, gil, python
The idea of multi-processing
map() for Python is quite nice. And what about multi-threaded one? Threads usually cause less overhead than processes. If a mapping function is quite side-effect free (even if it does some HTTP GETs — they are idempotent), you don’t rely on a parallel execution model you’ve selected. And when it isn’t, then such an approach is error-prone. I’ve implemented a very simple threaded exception-aware
map() using one thread per call. This is the basic usage scenario:
@measured def single_threaded(): return [urlopen(url) for x in range(count)] @measured def multi_threaded(): return map(lambda x: urlopen(url), range(count)) ps_s = single_threaded() ps_m = multi_threaded()
The results for
url = "http://ya.ru/" and
count = 1000:
single_threaded() is finished in 121.333 s multi_threaded() is finished in 29.692 s
map() is rather useful, isn’t it?
P. S. The first exception in a
map() thread will be re-raised (with its traceback) in the main thread while others will be suppressed.