Python开发【笔记】：关于子线程（子进程）与主线程（主进程）的关联

前言：

主要分析下面的问题：

• 主线程启线程  主线程执行完毕，会关闭子线程吗？
• 子线程启线程  主线程执行完毕，会结束吗？
• 主进程启动进程，主进程执行完毕，会怎样？
• 子进程启动进程，进程执行完毕，又会如何？

1、主线程启线程

示例1.1

import time
import threading

def function():
    time.sleep(2)
    print('sub thread [%s] execute done' % threading.currentThread().ident)

def main():
    threading.Thread(target=function).start()

    print('main thread [%s] execute done'%threading.currentThread().ident)

if __name__ == '__main__':
    main()

# main thread [11920] execute done
# sub thread [8876] execute done

主线程执行完毕，等待子线程执行；若想主线程执行完毕，直接退出，需设置守护线程

示例1.2

import time
import threading

def function():
    time.sleep(2)
    print('sub thread [%s] execute done' % threading.currentThread().ident)

def main():
    t = threading.Thread(target=function)
    t.setDaemon(True)
    t.start()
    print('main thread [%s] execute done'%threading.currentThread().ident)

if __name__ == '__main__':
    main()

# main thread [3052] execute done

　　

 2、子线程启动线程

示例2.1

import time
import threading

def function():
    time.sleep(2)
    threading.Thread(target=subfunction).start()
    print('sub thread [%s] execute done' % threading.currentThread().ident)

def subfunction():
    time.sleep(2)
    print('sub thread [%s] execute done' % threading.currentThread().ident)

def main():
    threading.Thread(target=function).start()

    print('main thread [%s] execute done'%threading.currentThread().ident)

if __name__ == '__main__':
    main()

# main thread [2288] execute done
# sub thread [9556] execute done
# sub thread [12156] execute done

如示例1.1一致，主线程会等待子子线程执行完毕，然后关闭

 

 3、主进程启动进程

示例2.1

import os
import time
import multiprocessing

def function():
    time.sleep(2)
    print('sub process [%s] execute done' % os.getpid())

def main():
    multiprocessing.Process(target=function).start()
    print('main process [%s] execute done'%os.getpid())

if __name__ == '__main__':
    main()

# main process [5628] execute done
# sub process [11060] execute done

主进程会等待子进程执行完毕后关闭

 4、子进程启动进程

示例4.1

import os
import time
import multiprocessing

def function():
    time.sleep(2)
    print('sub process [%s] execute done' % os.getpid())

def main():
    pid = os.fork()
    print(pid)
    if pid > 0:
        return
    multiprocessing.Process(target=function).start()
    print('main process [%s] execute done'%os.getpid())

if __name__ == '__main__':
    main()

# 20533
# 0
# main process [20533] execute done
# sub process[20534] execute done

子进程会等待进程执行完毕后关闭