如何使用多线程使我的代码不在 Python 中按顺序运行

Question

I created simple code which sum the array using Python and multithreading, but I know that It works sequentially. My question is, how can I change my code to not work sequentially using multithreading? The code:

import threading
def sum(n, **totalSum):
    sumThreads['sumThreads'] += matrix[n]

sumThreads = {"sumThreads":0}
for i in range(len(matrix)):
    t = threading.Thread(target=sum, args=(i,), kwargs=sumThreads)
    t.start()
    t.join()
print("Suma: ",sumThreads['sumThreads'])

I tried to achive it using multiprocessing like so:

if __name__ == '__main__':
    import multiprocessing
    my_input = [6,5,4,3,2,1,0]
    # Pool over all CPUs
    print(sum(multiprocessing.Pool().map(int, my_input)))

but I need to use multithreading. Any help would be greatly appreciated!

Answer 1

You cannot share your list my_input between processes. A good strategy is to split your data into small chunks then compute partial data and finally process all partial results:

You code could be:

import multiprocessing as mp
import time
import random

CHUNKSIZE = 5

def partial_sum(l):
    # Include a latency for demo
    time.sleep(random.random())
    s = sum(l)
    print(f"Sum of {str(l):<15}: {s:>3}")
    return s

if __name__ == '__main__':
    my_input = range(100)
    chunks = (my_input[i:i+CHUNKSIZE]
                  for i in range(0, len(my_input), CHUNKSIZE))

    with mp.Pool(mp.cpu_count()) as pool:
        global_sum = sum(pool.map(partial_sum, chunks))
    print('---------------------------')
    print(f"Global total: {global_sum}")

Output:

Sum of range(35, 40)  : 185
Sum of range(5, 10)   :  35
Sum of range(70, 75)  : 360
Sum of range(50, 55)  : 260
Sum of range(55, 60)  : 285
Sum of range(10, 15)  :  60
Sum of range(45, 50)  : 235
Sum of range(40, 45)  : 210
Sum of range(95, 100) : 485
Sum of range(25, 30)  : 135
Sum of range(75, 80)  : 385
Sum of range(90, 95)  : 460
Sum of range(20, 25)  : 110
Sum of range(60, 65)  : 310
Sum of range(30, 35)  : 160
Sum of range(85, 90)  : 435
Sum of range(65, 70)  : 335
Sum of range(15, 20)  :  85
Sum of range(80, 85)  : 410
Sum of range(0, 5)    :  10
---------------------------
Global total: 4950