当进程是守护进程时，python 的多处理模块的 join()

Question

我很困惑为什么下面的代码块会这样工作。当进程是守护进程且不调用 join() 时与调用 join() 时。当它不调用 join() 时，看起来主进程终止，并且守护进程在主进程终止后都终止:

from multiprocessing import Process
import os

def info(title):
    print(title)
    print('module name:', __name__)
    if hasattr(os, 'getppid'):  # only available on Unix
        print('parent process:', os.getppid())
    print('process id:', os.getpid())

def f(name):
    info('function f')
    print('hello', name)

if __name__ == '__main__':
    info('main line')
    p = Process(target=f, args=('bob',))
    p.daemon = True
    p.start()
    #p.join()

输出:

main line
module name: __main__
parent process: 290
process id: 4793

join() 被调用:

from multiprocessing import Process
import os

def info(title):
    print(title)
    print('module name:', __name__)
    if hasattr(os, 'getppid'):  # only available on Unix
        print('parent process:', os.getppid())
    print('process id:', os.getpid())

def f(name):
    info('function f')
    print('hello', name)

if __name__ == '__main__':
    info('main line')
    p = Process(target=f, args=('bob',))
    p.daemon = True
    p.start()
    p.join()

输出:

main line
module name: __main__
parent process: 290
process id: 4807
function f
module name: __main__
parent process: 4807
process id: 4808
hello bob

Answer 1

是的，你说得对。当主进程终止时，守护进程也将终止。 此页面将为您提供更多详细信息:Why is a Python multiprocessing daemon process not printing to standard output?