多处理查找区间中的素数

Question

in python 3 i have to find prime numbers in an interval [a,b] using multiprocessing pipes in specific , here is my code :

 import sys
    import multiprocessing
    import os
    import time

def isprime(conn):
    while 1:
        num = conn.recv()
        print(num)
        if num < 2:
            return None
        for i in range(2, num):
            if (num % i) == 0:
                return None
        else:
            print(num)

def psend(conn,num):
    for i in num:
        conn.send(i)

if __name__ == "__main__":
    pid = os.fork()
    p_conn, c_conn = multiprocessing.Pipe()
    start_time = time.perf_counter()
    p1 = multiprocessing.Process(target=psend, args=(p_conn,range(0,31)))
    p2 = multiprocessing.Process(target=isprime, args=(c_conn,))
    p1.start()
    p2.start()
    
    finish_time = time.perf_counter()
    print(f"Program finished in {finish_time-start_time} seconds")
    

i expected to get all prime numbers but the child get only the first number which is :0 then it closed

Answer 1

When a Process target returns, it ends. Therefore, for this scenario, it has to run in a loop and somehow know when to stop processing.

In this example, we send values from a range then, once the range is exhausted, we send -1 as an indication that a no more data will be sent.

from multiprocessing import Pipe, Process
from sympy import isprime as ISPRIME
from time import perf_counter

def isprime(p):
    while (n := p.recv()) >= 0:
        if ISPRIME(n):
            print(n)

def psend(p, num):
    for i in num:
        p.send(i)
    p.send(-1) # inform isprime() function that no more data will be sent

def main():
    start = perf_counter()
    p, c = Pipe(False)
    (p1 := Process(target=psend, args=(c, range(0, 31)))).start()
    (p2 := Process(target=isprime, args=(p,))).start()
    end = perf_counter()
    for p in p1, p2:
        p.join()
    print(f'Duration = {end-start:.4f}s')

if __name__ == '__main__':
    main()

Output:

2
3
5
7
11
13
17
19
23
29
Duration = 0.0095s