Python多线程:主线程等待所有子线程结束代码

from time import ctime
import threading
import time

def a():
  #for i in range(5):
    print('Program a is running... at ', ctime(),u'.线程名为：',threading.current_thread().name )
    time.sleep(0.2)
   
def b(x):
  #for i in range(5):
    print('Program b('+x+') is running... at ', ctime(),u'.线程名为：',threading.current_thread().name )
    time.sleep(0.1)
   

if __name__ == '__main__':
  print('Mainthread %s is running...' % threading.current_thread().name)
  thread_list = []
  for i in range(400):#同时运行多个
   t1= threading.Thread(target=a)
   thread_list.append(t1)
   
  t2 = threading.Thread(target=b, args=('Python',))
  thread_list.append(t2)
  t3 = threading.Thread(target=b, args=('Java',))
  thread_list.append(t3)
 

  for t in thread_list:
    t.setDaemon(True) # 设置为守护线程，不会因主线程结束而中断
    t.start()
  for t in thread_list:
    t.join() # 子线程全部加入，主线程等所有子线程运行完毕

  print('Mainthread %s ended.' % threading.current_thread().name)