Multiprocessing : use tqdm to display a progress bar

Question

To make my code more "pythonic" and faster, I use "multiprocessing" and a map function to send it a) the function and b) the range of iterations.

The implanted solution (i.e., call tqdm directly on the range tqdm.tqdm(range(0, 30)) does not work with multiprocessing (as formulated in the code below).

The progress bar is displayed from 0 to 100% (when python reads the code?) but it does not indicate the actual progress of the map function.

How to display a progress bar that indicates at which step the 'map' function is ?

from multiprocessing import Pool
import tqdm
import time

def _foo(my_number):
   square = my_number * my_number
   time.sleep(1)
   return square 

if __name__ == '__main__':
   p = Pool(2)
   r = p.map(_foo, tqdm.tqdm(range(0, 30)))
   p.close()
   p.join()

Any help or suggestions are welcome...

Answer 1

Use imap instead of map, which returns an iterator of processed values.

from multiprocessing import Pool
import tqdm
import time

def _foo(my_number):
   square = my_number * my_number
   time.sleep(1)
   return square 

if __name__ == '__main__':
   with Pool(2) as p:
      r = list(tqdm.tqdm(p.imap(_foo, range(30)), total=30))

Answer 2

Solution Found : Be careful! Due to multiprocessing, estimation time (iteration per loop, total time, etc.) could be unstable, but the progress bar works perfectly.

Note: Context manager for Pool is only available from Python version 3.3

from multiprocessing import Pool
import time
from tqdm import *

def _foo(my_number):
   square = my_number * my_number
   time.sleep(1)
   return square 

if __name__ == '__main__':
    with Pool(processes=2) as p:
        max_ = 30
        with tqdm(total=max_) as pbar:
            for i, _ in tqdm(enumerate(p.imap_unordered(_foo, range(0, max_)))):
                pbar.update()

Answer 3

based on the answer of Xavi Martínez I wrote the function imap_unordered_bar. It can be used in the same way as imap_unordered with the only difference that a processing bar is shown.

from multiprocessing import Pool
import time
from tqdm import *

def imap_unordered_bar(func, args, n_processes = 2):
    p = Pool(n_processes)
    res_list = []
    with tqdm(total = len(args)) as pbar:
        for i, res in tqdm(enumerate(p.imap_unordered(func, args))):
            pbar.update()
            res_list.append(res)
    pbar.close()
    p.close()
    p.join()
    return res_list

def _foo(my_number):
    square = my_number * my_number
    time.sleep(1)
    return square 

if __name__ == '__main__':
    result = imap_unordered_bar(_foo, range(5))

Answer 4

You can use p_tqdm instead.

https://github.com/swansonk14/p_tqdm

from p_tqdm import p_map
import time

def _foo(my_number):
   square = my_number * my_number
   time.sleep(1)
   return square 

if __name__ == '__main__':
   r = p_map(_foo, list(range(0, 30)))

Answer 5

This approach simple and it works.

from multiprocessing.pool import ThreadPool
import time
from tqdm import tqdm

def job():
    time.sleep(1)
    pbar.update()

pool = ThreadPool(5)
with tqdm(total=100) as pbar:
    for i in range(100):
        pool.apply_async(job)
    pool.close()
    pool.join()