I use the python 'multiprocessing' module to run single processes on multiple cores but I want to run a couple of independent processes in parallel.
For example, Process-one parses large files, Process-two find patterns in different files and process three does some calculation; can all these three different processed that have different sets of arguments be run in parallel?
def Process1(largefile):
Parse large file
runtime 2hrs
return parsed_file
def Process2(bigfile)
Find pattern in big file
runtime 2.5 hrs
return pattern
def Process3(integer)
Do astronomical calculation
Run time 2.25 hrs
return calculation_results
def FinalProcess(parsed,pattern,calc_results):
Do analysis
Runtime 10 min
return final_results
def main():
parsed = Process1(largefile)
pattern = Process2(bigfile)
calc_res = Process3(integer)
Final = FinalProcess(parsed,pattern,calc_res)
if __name__ == __main__:
main()
sys.exit()
In the above pseudo-code Process1, Process2 and Process3 are single-core processes ie they can't be run on multiple processors. These processes are run sequentially and take 2+2.5+2.25hrs = 6.75 hrs. Is it possible to run these three processes in parallel? So that they run at the same time on different processors/cores and when most time taking (Process2) finishes than we move to Final Process.
From 16.6.1.5. Using a pool of workers :
from multiprocessing import Pool
def f(x):
return x*x
if __name__ == '__main__':
pool = Pool(processes=4) # start 4 worker processes
result = pool.apply_async(f, [10]) # evaluate "f(10)" asynchronously
print result.get(timeout=1) # prints "100" unless your computer is *very* slow
print pool.map(f, range(10)) # prints "[0, 1, 4,..., 81]"
You can, therefore, apply_async against a pool and get your results after everything is ready.
from multiprocessing import Pool
# all your methods declarations above go here
# (...)
def main():
pool = Pool(processes=3)
parsed = pool.apply_async(Process1, [largefile])
pattern = pool.apply_async(Process2, [bigfile])
calc_res = pool.apply_async(Process3, [integer])
pool.close()
pool.join()
final = FinalProcess(parsed.get(), pattern.get(), calc_res.get())
# your __main__ handler goes here
# (...)
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