初识Python多线程中的setDaemon与join

正常多线程代码

import threading
import time

def runThread1():
    time1 = time.time()
    print("runThread1 starting")
    time.sleep(8)
    print("runThread1 ending")
    time2 = time.time()
    print("runThread1 time : ",(time2 - time1)) # 计算程序运行时间，理论值8
       
def runThread2():
    flag = 3
    time1 = time.time()
    print("runThread2 starting")
    while flag:
        print("Hello")
        flag -= 1
        time.sleep(2)
    print("runThread2 ending")
    time2 = time.time()
    print("runThread2 time : ",(time2 - time1)) # 计算程序运行时间，理论值6
   
if __name__ == '__main__':
    runThread1 = threading.Thread(target = runThread1)
    runThread2 = threading.Thread(target = runThread2)
    
    runThread1.start()
    runThread2.start()

    print("main end")

运行结果

runThread1 starting
runThread2 starting
main end
Hello
Hello
Hello
runThread2 ending
runThread2 time :  6.001581907272339
runThread1 ending
runThread1 time :  8.001220941543579

结果分析

两个线程正常运行并正常结束，main end 在线程执行时正常输出

---

setDaemon 测试

import threading
import time

def runThread1():
    time1 = time.time()
    print("runThread1 starting")
    time.sleep(8)
    print("runThread1 ending")
    time2 = time.time()
    print("runThread1 time : ",(time2 - time1)) # 计算程序运行时间，理论值8
       
def runThread2():
    flag = 3
    time1 = time.time()
    print("runThread2 starting")
    while flag:
        print("Hello")
        flag -= 1
        time.sleep(2)
    print("runThread2 ending")
    time2 = time.time()
    print("runThread2 time : ",(time2 - time1)) # 计算程序运行时间，理论值6
   
if __name__ == '__main__':
    runThread1 = threading.Thread(target = runThread1)
    runThread2 = threading.Thread(target = runThread2)
    runThread1.setDaemon(True)
    
    runThread1.start()
    runThread2.start()
    
    print("main end")

运行结果

runThread1 starting
runThread2 starting
main end
Hello
Hello
Hello
runThread2 ending
runThread2 time :  6.00260591506958

结果分析

Thread2本该运行8秒后结束，但通过设置setDaemon方法设置后，在Thread1运行6秒并结束后Thread2也立刻随之结束。原因是Thread2在Main线程（__main__所在线程）中创建，Thread2调用setDaemon(True)后，即将Main线程设置为Thread2的守护线程，即当Mian线程结束时无论Thread2有没有结束都会强制结束，而因为Main线程不是Thread1的守护线程，所以Main线程等待Thread1结束后才结束。

---

setDeamon 测试2

import threading
import time

def runThread1():
    time1 = time.time()
    print("runThread1 starting")
    time.sleep(8)
    print("runThread1 ending")
    time2 = time.time()
    print("runThread1 time : ",(time2 - time1)) # 计算程序运行时间，理论值8
       
def runThread2():
    flag = 3
    time1 = time.time()
    print("runThread2 starting")
    while flag:
        print("Hello")
        flag -= 1
        time.sleep(2)
    print("runThread2 ending")
    time2 = time.time()
    print("runThread2 time : ",(time2 - time1)) # 计算程序运行时间，理论值6
   
if __name__ == '__main__':
    runThread1 = threading.Thread(target = runThread1)
    runThread2 = threading.Thread(target = runThread2)
    runThread1.setDaemon(True)
    runThread2.setDaemon(True)
    runThread2.start() # 6
    runThread1.start() # 8
    
    print("main end")

运行结果

runThread2 starting
Hello
runThread1 starting
main end

结果分析

将Thread1、Thread2都设置setDaemon(True)后，在主程序输出完main end后结束的时候也都被强行结束。

---

join测试

import threading
import time

def runThread1():
    time1 = time.time()
    print("runThread1 starting")
    time.sleep(8)
    print("runThread1 ending")
    time2 = time.time()
    print("runThread1 time : ",(time2 - time1)) # 计算程序运行时间，理论值8
       
def runThread2():
    flag = 3
    time1 = time.time()
    print("runThread2 starting")
    while flag:
        print("Hello")
        flag -= 1
        time.sleep(2)
    print("runThread2 ending")
    time2 = time.time()
    print("runThread2 time : ",(time2 - time1)) # 计算程序运行时间，理论值6
   
if __name__ == '__main__':
    runThread1 = threading.Thread(target = runThread1)
    runThread2 = threading.Thread(target = runThread2)
    #runThread1.setDaemon(True)
    
    runThread1.start()
    runThread2.start()
    
    runThread2.join()
    
    print("main end")

运行结果

runThread1 starting
runThread2 starting
Hello
Hello
Hello
runThread2 ending
runThread2 time :  6.001340389251709
main end
runThread1 ending
runThread1 time :  8.000601291656494

结果分析

main end 在Thread2运行完成后才输出，说明Thread2.join()表示等待Thread2线程结束，未结束的话一直在这里等待，线程结束后才执行后续的语句

---

setDaemon & join

import threading
import time

def runThread1():
    time1 = time.time()
    print("runThread1 starting")
    time.sleep(8)
    print("runThread1 ending")
    time2 = time.time()
    print("runThread1 time : ",(time2 - time1)) # 计算程序运行时间，理论值8
       
def runThread2():
    flag = 3
    time1 = time.time()
    print("runThread2 starting")
    while flag:
        print("Hello")
        flag -= 1
        time.sleep(2)
    print("runThread2 ending")
    time2 = time.time()
    print("runThread2 time : ",(time2 - time1)) # 计算程序运行时间，理论值6
   
if __name__ == '__main__':
    runThread1 = threading.Thread(target = runThread1)
    runThread2 = threading.Thread(target = runThread2)
    runThread1.setDaemon(True)
    runThread2.setDaemon(True)
    runThread2.start() # 6
    
    runThread1.start() # 8
    
    runThread2.join() 
    
    print("main end")

运行结果

runThread2 starting
Hello
runThread1 starting
Hello
Hello
runThread2 ending
runThread2 time :  6.003632545471191
main end

结果分析

Main线程被设置为Thread1的守护线程,Main线程在Thread2结束并输出main end后结束，Thread1也被强行结束