多进程在运行的时候只有一个子进程会运行，怎么解决？

我用python写的多进程爬虫，在linux服务器上运行的时候，不管我设置多少个进程，每次都只有一个子进程运行。
主函数是这样的，mainFunction是我爬虫的主要函数，现在每次都只有第一个进程运行，就是参数是0的那一个。
因为爬虫I/O不算密集，所以没用多线程。另外进程之间是独立的。
我的目标是10个进程同时运行，我有10个API的key，数据也分成10块来抓，这里mainFunction里的参数就是为了对应要用的key和要抓的数据。

if __name__ == '__main__':
    print('Started at ', datetime.now())

    processes = []
    for i in range(0,10):
        t = multiprocessing.Process(target = mainFunction, args = (i,))
        processes.append(t)
    for t in processes:
        t.start()
        t.join()

    print('Finished at ', datetime.now())

麻烦大佬们帮忙找找原因，谢谢！

这段代码，每次循环都是start一个线程，并等待结束后再开始下一个线程。

    for t in processes:
        t.start()
        t.join()

改为：

    for t in processes:
        t.start()
    for t in processes:
        t.join()

完整的测试代码:

import time
import multiprocessing
from datetime import datetime

def mainFunction(idx,running):
    print('thread {0} is running.'.format(idx))
    while(running.value):
        pass
    print('thread {0} is closing .'.format(idx))

if __name__ == '__main__':
    running = multiprocessing.Value('i',1)
    print('Started at ', datetime.now())
    processes = []
    for i in range(0,10):
        t = multiprocessing.Process(target = mainFunction, args = (i,running,))
        processes.append(t)
    for t in processes:
        t.start()

    time.sleep(10)
    running.value = 0

运行结果:

('Started at ', datetime.datetime(2020, 5, 14, 11, 9, 47, 862220))
thread 0 is running.
thread 1 is running.
thread 2 is running.
thread 3 is running.
thread 4 is running.
thread 5 is running.
thread 7 is running.
thread 6 is running.
thread 9 is running.
thread 8 is running.
thread 1 is closing.
thread 7 is closing.
thread 2 is closing.
thread 3 is closing.
thread 0 is closing.
thread 5 is closing.
thread 4 is closing.
thread 9 is closing.
thread 6 is closing.
thread 8 is closing.
('Finished at ', datetime.datetime(2020, 5, 14, 11, 9, 57, 989041))