If it won't be simple, it simply won't be. [source code] by Miki Tebeka, CEO, 353Solutions

Friday, April 03, 2009

pmap

#!/usr/bin/env python
'''Parallel map (Unix only)'''

__author__ = "Miki Tebeka <miki.tebeka@gmail.com>"

# The big advantage of this implementation is that "fork" is very fast on
# copying data, so if you pass big arrays as arguments and return small values
# this is a win

# FIXME
# * For too many items, we get "Too many open files"
# * Handle child exceptions

from os import fork, pipe, fdopen, waitpid, P_WAIT
from marshal import dump, load
from itertools import takewhile, count

def spawn(func, data):
read_fo, write_fo = map(fdopen, pipe(), ("rb", "wb"))
pid = fork()
if pid: # Parent
return pid, read_fo

# Child
dump(func(data), write_fo)
write_fo.close()
raise SystemExit

def wait(child):
pid, fo = child
waitpid(pid, P_WAIT)
value = load(fo)
fo.close()
return value

def pmap(func, items):
'''
>>> pmap(lambda x: x * 2, range(5))
[0, 2, 4, 6, 8]
'''
children = map(lambda item: spawn(func, item), items)
return map(wait, children)

if __name__ == "__main__":
def fib(n):
a, b = 1, 1
while n > 1:
a, b = b, a + b
n -= 1
return b

items = range(10)
print "pmap(fib, %s)" % str(items)
print pmap(fib, items)
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