python的多处理模块的进程为守​​护程序时的join（）

Question

我很困惑为什么下面的代码块以这种方式工作。当进程是守护程序并且不调用join（）时，它何时调用join（）。当不调用join（）时，似乎主进程终止，并且守护进程都在主进程终止后终止：

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（）称为：

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，您是对的。当主进程终止时，守护进程也将终止。 该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?