一文说懂join和setDaemon

 最精简的知识点：

1、主线程退出，子线程还可以在跑。线程之间都无关

 

2、守护线程会被其他最后一个线程或主线程终止。监听谁 就把谁设置守护线程

3、想在主线程结束前跑完子线程，用join().

----------------------------------

这里有个小疑问，既然加不加join子线程都会跑完，为什么还加join。因为有些线程之间需要输出参数给其余函数用，所以得等某个函数线程跑完才能执行主线程。

1 先记住三句话

主线程退出，进程等待所有子线程执行完毕后才结束

主线程结束后进程不等待守护线程完成，立即结束     setDaemon(True)

主线程等待子线程完成后结束 join

 

2 作用

1）想先停主线程，先跑子现程用join

2）想监听某个函数，超时后关闭这个函数，设立这个函数的线程为守护线程。

3）最常见的连用方式  thr.setDaemon(True),  后面thr.join()   注意不用加时间。或者加一个超时时间，超时时间一到主线程执行，执行结束后，进程自动关闭守护子线程。

 

仔细理解下面两个功能代码：

1 超时器

import time
#from threading import Thread
import threading
import sys

class KThread(threading.Thread):
    """A subclass of threading.Thread, with a kill()
    method.
    
    Come from:
    Kill a thread in Python: 
    http://mail.python.org/pipermail/python-list/2004-May/260937.html
    """
    def __init__(self, *args, **kwargs):
        threading.Thread.__init__(self, *args, **kwargs)
        self.killed = False

    def start(self):
        """Start the thread."""
        self.__run_backup = self.run
        self.run = self.__run      # Force the Thread to install our trace.
        threading.Thread.start(self)

    def __run(self):
        """Hacked run function, which installs the
        trace."""
        sys.settrace(self.globaltrace)
        self.__run_backup()
        self.run = self.__run_backup

    def globaltrace(self, frame, why, arg):
        if why == 'call':
          return self.localtrace
        else:
          return None

    def localtrace(self, frame, why, arg):
        if self.killed:
          if why == 'line':
            raise SystemExit()
        return self.localtrace

    def kill(self):
        self.killed = True

class Timeout(Exception):
    """function run timeout"""
    
def timeout(seconds = 3):
    def timeout_decorator(func):        
        def _new_func(oldfunc, result, oldfunc_args, oldfunc_kwargs):
            result.append(oldfunc(*oldfunc_args, **oldfunc_kwargs))
        
        def _(*args, **kwargs):
            result = []
            new_kwargs = { # create new args for _new_func, because we want to get the func return val to result list
                'oldfunc': func,
                'result': result,
                'oldfunc_args': args,
                'oldfunc_kwargs': kwargs
            }
            thd = KThread(target=_new_func, args=(), kwargs=new_kwargs)
            thd.setDaemon(True)
            thd.start()
            thd.join(seconds)
            #alive = thd.isAlive() 版本isAlive转为is_alive
            alive = thd.is_alive()
            thd.kill()
            #try:
                #if alive:
                    #raise Timeout(u'function run too long, timeout %d seconds.' % seconds)
                #else:
                    #if len(result) == 0:
                        #raise Exception("TESTCASE FAILED")
                    #else:
                        #return result[0]
            #except Exception as e:
                #print("toolong",e)
                
            if alive:
                raise Timeout(u'function run too long, timeout %d seconds.' % seconds)
            else:
                if len(result) == 0:
                    raise Exception("TESTCASE FAILED")
                else:
                    return result[0]
        _.__name__ = func.__name__
        _.__doc__ = func.__doc__
        return _
    return timeout_decorator

@timeout(3)
def fun():
    print("111231111111---")
    time.sleep(100)
    print("===")
@timeout(3)
def fun0():
    print("11111")
    time.sleep(2)
    
    print("end")
    return 10001
    
#fun()
#print(fun0())
def tr(sce):
    def wrap(fun):
        def deco():
            print("-=====", sce)
            fun()
            print("_==========")
        return deco
    return wrap
@tr(3)
def runt():
    print("run111111111===",runt.__name__)

#runt()

 

2 监听某个目录下文件是否生成

import os
import time
import threading
RET=0
def wrap(func):
    def lis_file(dirname,name,epch=30,tim=0.1):
        print("===lis_file")
        print("epch===",epch)
        global RET
        print("RET===",RET)
        c=1
        while c<=epch:
            print("=== %s==="%c)
            file_list = os.listdir(dirname)
            if name in file_list:
                
                RET=True
                print("===",RET)
                return RET
            time.sleep(tim)
            
            c+=1
        print("c=====",c)
        RET=False
        return RET
    def _(*args):
        lis = threading.Thread(target=lis_file,args=(args))
        ft = threading.Thread(target=func,args=(args))
        #lis.setDaemon(False)
        # 想设立守护线程，即哪个函数需要被监控就设立哪个函数为守护现程。
        # 这个守护现程一定掩护所有现程子主线程全部跑完才能结束。
        ft.setDaemon(True)
        lis.start()
        ft.start()
        #func(*args)
        # join加入容器，会先跑容器中的线程，然后再回到主线程
        # join 1 表示主线程等子线程1s后结束，然后子线程还继续跑
        # 画出现程关系图 join为主现程一直等待子线程
        # 不叫join 为 主线程跑 子线程跑 子现程跑  主线程结束，子现程结束
        ft.join()
        print("============")
    return _

@wrap
def fun(dirname,name,epch=30,tim=0.1):
    print("start===")
    time.sleep(10)
    with open("shiyan.txt","w") as f:
        f.write("===")
    print("end===")

d=r"C:\Users\devevf\Documents\AItest\shiyan"
name=r"shiyan.txt"
fun(d,name,30,0.1)

 

3 为了验证setDaemon

注意 跑带有setDaemon时一定在cmd执行py脚本，在ide中没有setDaemon效果

import threading
import time


def child_thread1():
    
    for i in range(10):
        time.sleep(1)
        with open("setd111.txt","a") as f:
            f.write(str(i))
        print('child_thread1_running...')


def child_thread2():
    with open("setd222.txt","a") as f:
        for i in range(1):
            time.sleep(1)
            f.write(str(i))
            print('child_thread2_running...')


def parent_thread():
    print('parent_thread_running...')
    thread1 = threading.Thread(target=child_thread1)
    thread2 = threading.Thread(target=child_thread2)
    # 注意ide体现不出来，在cmd里面执行会明显
    # 守护线程，当前进程结束线程立即结束，或者是主线程结束立即结束
    # 主线程结束后进程不等待守护线程完成，立即结束
    # 实验为 守护线程或长或短都不影响主线程的结束
    # 守护线程 一定等所有线程结束才能结束
    # 两个守护线程 按照谁的进度，谁都不按照，只是按照主线程
    thread1.setDaemon(True)
    #thread2.setDaemon(True)
    thread1.start()
    thread2.start()
    print('parent_thread_exit...')
    time.sleep(1)
    with open("main_file.txt","w") as f:
        f.write("mainfile")
    print("main bu shou yingxiang====yanzheng kongzhi jincheng")


if __name__ == "__main__":
    parent_thread()
    

　　

 

 

 

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参考下文，若精炼内容没有理解清楚请看参考，例子都很经典。

python主线程与子线程的结束顺序

 

引用自 主线程退出对子线程的影响--YuanLi 的一段话：

对于程序来说，如果主进程在子进程还未结束时就已经退出，那么Linux内核会将子进程的父进程ID改为1（也就是init进程），当子进程结束后会由init进程来回收该子进程。

主线程退出后子线程的状态依赖于它所在的进程，如果进程没有退出的话子线程依然正常运转。如果进程退出了，那么它所有的线程都会退出，所以子线程也就退出了。

主线程退出，进程等待所有子线程执行完毕后才结束

进程启动后会默认产生一个主线程，默认情况下主线程创建的子线程都不是守护线程（setDaemon(False)）。因此主线程结束后，子线程会继续执行，进程会等待所有子线程执行完毕后才结束

所有线程共享一个终端输出（线程所属进程的终端）

import threading
import time


def child_thread1():
    for i in range(100):
        time.sleep(1)
        print('child_thread1_running...')


def parent_thread():
    print('parent_thread_running...')
    thread1 = threading.Thread(target=child_thread1)
    thread1.start()
    print('parent_thread_exit...')


if __name__ == "__main__":
    parent_thread()

输出为：

parent_thread_running...
parent_thread_exit...
child_thread1_running...
child_thread1_running...
child_thread1_running...
child_thread1_running...
...

可见父线程结束后，子线程仍在运行，此时结束进程，子线程才会被终止

主线程结束后进程不等待守护线程完成，立即结束

当设置一个线程为守护线程时，此线程所属进程不会等待此线程运行结束，进程将立即结束

import threading
import time


def child_thread1():
    for i in range(100):
        time.sleep(1)
        print('child_thread1_running...')


def child_thread2():
    for i in range(5):
        time.sleep(1)
        print('child_thread2_running...')


def parent_thread():
    print('parent_thread_running...')
    thread1 = threading.Thread(target=child_thread1)
    thread2 = threading.Thread(target=child_thread2)
    thread1.setDaemon(True)
    thread1.start()
    thread2.start()
    print('parent_thread_exit...')


if __name__ == "__main__":
    parent_thread()

输出：

parent_thread_running...
parent_thread_exit...
child_thread1_running...child_thread2_running...

child_thread1_running...child_thread2_running...

child_thread1_running...child_thread2_running...

child_thread1_running...child_thread2_running...

child_thread2_running...child_thread1_running...

Process finished with exit code 0

thread1是守护线程，thread2非守护线程，因此，进程会等待thread2完成后结束，而不会等待thread1完成

注意：子线程会继承父线程中daemon的值，即守护线程开启的子线程仍是守护线程

主线程等待子线程完成后结束

在线程A中使用B.join()表示线程A在调用join()处被阻塞，且要等待线程B的完成才能继续执行

import threading
import time


def child_thread1():
    for i in range(10):
        time.sleep(1)
        print('child_thread1_running...')


def child_thread2():
    for i in range(5):
        time.sleep(1)
        print('child_thread2_running...')


def parent_thread():
    print('parent_thread_running...')
    thread1 = threading.Thread(target=child_thread1)
    thread2 = threading.Thread(target=child_thread2)
    thread1.setDaemon(True)
    thread2.setDaemon(True)
    thread1.start()
    thread2.start()
    thread2.join()
    1/0
    thread1.join()
    print('parent_thread_exit...')


if __name__ == "__main__":
    parent_thread()

输出：

parent_thread_running...
child_thread1_running...
child_thread2_running...
child_thread1_running...
child_thread2_running...
child_thread1_running...
child_thread2_running...
child_thread1_running...
child_thread2_running...
child_thread1_running...
child_thread2_running...
Traceback (most recent call last):
  File "E:/test_thread.py", line 31, in <module>
    parent_thread()
  File "E:/test_thread.py", line 25, in parent_thread
    1/0
ZeroDivisionError: integer division or modulo by zero

主线程在执行到thread2.join()时被阻塞，等待thread2结束后才会执行下一句

1/0 会使主线程报错退出，且thread1设置了daemon=True，因此主线程意外退出时thread1也会立即结束。thread1.join()没有被主线程执行