I have a assignment for my course in Python.
The question is this :
You will write a program creating multiple processes (p=10). Each process will receive integer value (y) and compute y multiplying by 4 (y*4). A collection of y values is a list of integers [0, 1, 2, 3, 4, 5]. You must use a process pool, so you need to map these 10 processes to take the list of y integers. Do the following:
Your program should print out the following three. (1) Print out the original list. (2) Print each running process name and its output of y*4 in random order of execution
Output of (1): Input list: [0, 1, 2, 3, 4, 5]
Output of (2): Output in random order:
PoolWorker-10 output: [0, 4, 8, 12, 16, 20]
PoolWorker-11 output: [0, 4, 8, 12, 16, 20]
PoolWorker-12 output: [0, 4, 8, 12, 16, 20]
My first attempt was:
import time
from multiprocessing import Pool
from multiprocessing import Process, current_process
def f(number):
result=4*number
Process_name=current_process().name
print(f"Poolworker -{Process_name} output: {result} ")
return result
if __name__=='__main__':
p= Pool(processes=10)
numbers=[0,1,2,3,4,5]
result=p.map(f,numbers)
The output was:
Poolworker -SpawnPoolWorker-2 output: 0
Poolworker -SpawnPoolWorker-2 output: 4
Poolworker -SpawnPoolWorker-2 output: 8
Poolworker -SpawnPoolWorker-2 output: 12
Poolworker -SpawnPoolWorker-2 output: 16
Poolworker -SpawnPoolWorker-2 output: 20 My second attempt:
import time
from multiprocessing import Pool
from multiprocessing import Process, current_process
def f(*number):
numbers=list(number)
i=0
for x in numbers:
numbers[i]=4*numbers[i]
i+=1
Process_name=current_process().name
print(f"Poolworker -{Process_name}output: {numbers} ")
return numbers
if __name__ == '__main__':
array=[0,1,2,3,4,5]
p=Pool(processes=10)
result=p.map(f,array)
I still have the wrong output with the changes.
How can I get the desired output?
The issue is that f is applied to each number in your list whereas you want every worker to do the calculations on the whole list. Made some minor modifications to your code in order to get those results.
from itertools import repeat
from multiprocessing import Pool
from multiprocessing import Process, current_process
def f(numbers):
result= [4 * num for num in numbers]
name=current_process().name
print(f"Poolworker - {name} output: {result} ")
return result
if __name__=='__main__':
WORKERS = 10
p = Pool(processes=WORKERS)
numbers = [0, 1, 2, 3, 4, 5]
print(f"Original - {numbers}")
result = p.map(f, repeat(numbers, WORKERS))
This returns the following:
Original - [0, 1, 2, 3, 4, 5]
Poolworker - ForkPoolWorker-1 output: [0, 4, 8, 12, 16, 20]
Poolworker - ForkPoolWorker-2 output: [0, 4, 8, 12, 16, 20]
Poolworker - ForkPoolWorker-3 output: [0, 4, 8, 12, 16, 20]
Poolworker - ForkPoolWorker-4 output: [0, 4, 8, 12, 16, 20]
Poolworker - ForkPoolWorker-5 output: [0, 4, 8, 12, 16, 20]
Poolworker - ForkPoolWorker-6 output: [0, 4, 8, 12, 16, 20]
Poolworker - ForkPoolWorker-7 output: [0, 4, 8, 12, 16, 20]
Poolworker - ForkPoolWorker-8 output: [0, 4, 8, 12, 16, 20]
Poolworker - ForkPoolWorker-9 output: [0, 4, 8, 12, 16, 20]
Poolworker - ForkPoolWorker-10 output: [0, 4, 8, 12, 16, 20]