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., calling 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 can one 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

The simplest way is to use the iterative mapping (imap) function:

from multiprocessing import Pool
from tqdm 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(p.imap(_foo, range(0, 30)), total=30))

Answer 2

Solution found. Be careful! Due to multiprocessing, the 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 in Python 3.3+.

import time
from multiprocessing import Pool
from random import randint

from tqdm import tqdm


def _foo(my_number):
    square = my_number * my_number
    time.sleep(randint(1, 2) / 2)
    return square


if __name__ == "__main__":
    max_ = 30
    with Pool(processes=2) as p, tqdm(total=max_) as pbar:
        for result in p.imap(_foo, range(0, max_)):
            pbar.update()
            pbar.refresh()
            # do something with `result`

Answer 3

tqdm has released its own simple, elegant APIs for concurrent.

I give the following snippet as a straightforward example to illustrate multi-threading.

from tqdm.contrib.concurrent import thread_map

def f(row):
    x, y = row
    time.sleep(1)  # to visualize the progress

thread_map(f, [(x, y) for x, y in zip(range(1000), range(1000))])

Answer 4

Based on "user17242583" answer, I created the following function. It should be as fast as Pool.map and the results are always ordered. Plus, you can pass as many parameters to your function as you want and not just a single iterable.

from multiprocessing import Pool
from functools import partial
from tqdm import tqdm


def imap_tqdm(function, iterable, processes, chunksize=1, desc=None, disable=False, **kwargs):
    """
    Run a function in parallel with a tqdm progress bar and an arbitrary number of arguments.
    Results are always ordered and the performance should be the same as of Pool.map.
    :param function: The function that should be parallelized.
    :param iterable: The iterable passed to the function.
    :param processes: The number of processes used for the parallelization.
    :param chunksize: The iterable is based on the chunk size chopped into chunks and submitted to the process pool as separate tasks.
    :param desc: The description displayed by tqdm in the progress bar.
    :param disable: Disables the tqdm progress bar.
    :param kwargs: Any additional arguments that should be passed to the function.
    """
    if kwargs:
        function_wrapper = partial(_wrapper, function=function, **kwargs)
    else:
        function_wrapper = partial(_wrapper, function=function)

    results = [None] * len(iterable)
    with Pool(processes=processes) as p:
        with tqdm(desc=desc, total=len(iterable), disable=disable) as pbar:
            for i, result in p.imap_unordered(function_wrapper, enumerate(iterable), chunksize=chunksize):
                results[i] = result
                pbar.update()
    return results


def _wrapper(enum_iterable, function, **kwargs):
    i = enum_iterable[0]
    result = function(enum_iterable[1], **kwargs)
    return i, result

Answer 5

Use imap instead of map, which returns an iterator of the 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 6

import multiprocessing as mp
import tqdm


iterable = ... 
num_cpu = mp.cpu_count() - 2 # dont use all cpus.


def func():
    # your logic
    ...


if __name__ == '__main__':
    with mp.Pool(num_cpu) as p:
        list(tqdm.tqdm(p.imap(func, iterable), total=len(iterable)))

Answer 7

For progress bar with apply_async, we can use following code as suggested in:

https://github.com/tqdm/tqdm/issues/484

import time
import random
from multiprocessing import Pool
from tqdm import tqdm

def myfunc(a):
    time.sleep(random.random())
    return a ** 2

pool = Pool(2)
pbar = tqdm(total=100)

def update(*a):
    pbar.update()

for i in range(pbar.total):
    pool.apply_async(myfunc, args=(i,), callback=update)
pool.close()
pool.join()

Answer 8

Sorry for being late but if all you need is a concurrent map, I added this functionality in tqdm>=4.42.0:

from tqdm.contrib.concurrent import process_map  # or thread_map
import time

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

if __name__ == '__main__':
   r = process_map(_foo, range(0, 30), max_workers=2)

References: https://tqdm.github.io/docs/contrib.concurrent/ and https://github.com/tqdm/tqdm/blob/master/examples/parallel_bars.py

It supports max_workers and chunksize and you can also easily switch from process_map to thread_map.

Answer 9

Here is my take for when you need to get results back from your parallel executing functions. This function does a few things (there is another post of mine that explains it further) but the key point is that there is a tasks pending queue and a tasks completed queue. As workers are done with each task in the pending queue they add the results in the tasks completed queue. You can wrap the check to the tasks completed queue with the tqdm progress bar. I am not putting the implementation of the do_work() function here, it is not relevant, as the message here is to monitor the tasks completed queue and update the progress bar every time a result is in.

def par_proc(job_list, num_cpus=None, verbose=False):

# Get the number of cores
if not num_cpus:
    num_cpus = psutil.cpu_count(logical=False)

print('* Parallel processing')
print('* Running on {} cores'.format(num_cpus))

# Set-up the queues for sending and receiving data to/from the workers
tasks_pending = mp.Queue()
tasks_completed = mp.Queue()

# Gather processes and results here
processes = []
results = []

# Count tasks
num_tasks = 0

# Add the tasks to the queue
for job in job_list:
    for task in job['tasks']:
        expanded_job = {}
        num_tasks = num_tasks + 1
        expanded_job.update({'func': pickle.dumps(job['func'])})
        expanded_job.update({'task': task})
        tasks_pending.put(expanded_job)

# Set the number of workers here
num_workers = min(num_cpus, num_tasks)

# We need as many sentinels as there are worker processes so that ALL processes exit when there is no more
# work left to be done.
for c in range(num_workers):
    tasks_pending.put(SENTINEL)

print('* Number of tasks: {}'.format(num_tasks))

# Set-up and start the workers
for c in range(num_workers):
    p = mp.Process(target=do_work, args=(tasks_pending, tasks_completed, verbose))
    p.name = 'worker' + str(c)
    processes.append(p)
    p.start()

# Gather the results
completed_tasks_counter = 0

with tqdm(total=num_tasks) as bar:
    while completed_tasks_counter < num_tasks:
        results.append(tasks_completed.get())
        completed_tasks_counter = completed_tasks_counter + 1
        bar.update(completed_tasks_counter)

for p in processes:
    p.join()

return results

Answer 10

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()

Answer 11

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 12

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))