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I have a code like this:

def alpha():
    batch = list()
    batchSize = 25

    for i in range(frameNumber):
        frameData = doSomething()
        batch.append(frameData)

        if len(batch) == batchSize:
            result = beta(batch) # function to be parallelized
            continue
        else:
            continue

    print(completeResult) # here I want to have all results be joined

I need that every batchSize frames an instance of beta starts to compute those data using a thread. In the end, I would want to have all the results joined together (possibly in the correct order).

I tried this:

import concurrent.futures
from threading import Thread

def alpha():
    counter = 0
    batch = list()
    batchSize = 25
    completeResult = list()

    for i in range(frameNumber):
        frameData = doSomething()
        batch.append(frameData)

        if len(batch) == batchSize:
            with concurrent.futures.ThreadPoolExecutor() as executor:
                 counter = counter + 1
                 print('start thread ' + str(counter)
                 future = executor.submit(beta, batch)
                 result = future.result()
                 print('join thread ' + str(counter))
                 completeResult.append(result)
                 batch = []
    print(completeResult) # here I want to have all results be joined

but the execution is sequential because I have the following prints:

start thread 1
join thread 1
start thread 2 
join thread 2 
...

Then I tried using apply_async from multiprocessing.Pool but I have a problem. If I run:

import multiprocessing as mp
import os
import sys
import importlib.util
import main

results = []

def import_module_by_path(path):
    name = os.path.splitext(os.path.basename(path))[0]
    spec = importlib.util.spec_from_file_location(name, path)
    mod = importlib.util.module_from_spec(spec)
    spec.loader.exec_module(mod)
    return mod

def collect_result(result):
    global results
    results.append(result)

def doSomething(i, a,b,c,d):
    print('doSomething function')
    result = i
    return result

if __name__ == '__main__':
    pool = mp.Pool(mp.cpu_count())
  
    for i in range(0,4):
        pool.apply_async(doSomething, args=(i, 2, 3,4,5), callback=collect_result)
  
    pool.close()
    pool.join() 

    print(results)

it works fine. But if I run apply_async with an external function as following it doesn't work anymore:

import multiprocessing as mp
import os
import sys
import importlib.util
import main

results = []

def import_module_by_path(path):
    name = os.path.splitext(os.path.basename(path))[0]
    spec = importlib.util.spec_from_file_location(name, path)
    mod = importlib.util.module_from_spec(spec)
    spec.loader.exec_module(mod)
    return mod

def collect_result(result):
    global results
    results.append(result)

if __name__ == '__main__':
    fn = import_module_by_path('./myPythonFile.py')
    pool = mp.Pool(mp.cpu_count())
  
    for i in range(0,4):
        pool.apply_async(fn.myFunction, args=(i, 2, 3,4,5,6), callback=collect_result)

    pool.close()
    pool.join()

The problem is that it doesn't enter the function myFunction and the program finishes with exit code 0

grrfnc
  • 19
  • 8
  • 2
    You should look into threading, https://realpython.com/intro-to-python-threading/ as an example. Another option is subprocesses. Unfortunately the question too vague and in order to be able to help, we need to see what you tried and what worked (and what didn't). and if you have any specific issues feel free to ask further. Also check this: https://stackoverflow.com/help/how-to-ask – Zaid Al Shattle Feb 25 '21 at 11:11
  • @ZaidAlShattle I updated the question – grrfnc Feb 25 '21 at 12:03
  • Does this answer your question? [Is there a simple process-based parallel map for python?](https://stackoverflow.com/questions/1704401/is-there-a-simple-process-based-parallel-map-for-python) – Tomerikoo Feb 25 '21 at 13:28
  • @Tomerikoo no, because with map I need to have all inputs before calling the first thread. In this case I need to create a thread as soon as 25 frames are elapsed, I need an async method – grrfnc Feb 25 '21 at 15:04
  • Then check [`map_async`](https://docs.python.org/3/library/multiprocessing.html#multiprocessing.pool.Pool.map_async) – Tomerikoo Feb 25 '21 at 15:19
  • I used apply_async from multiprocessing.Pool but I have a problem: – grrfnc Feb 25 '21 at 15:22
  • @Tomerikoo i've updated the question – grrfnc Feb 25 '21 at 15:32

0 Answers0