线程执行的函数的return语句会自动杀死线程吗？

Question

After function2 executes and is returned, would the thread be killed automatically and do I need to join() the thread or do something to make sure that it is completely gone in function1?

def function1():
    a = 1
    b = 2
    Thread(target=function2, args=(a,b,)).start()

def function2(a, b):
    print(a + b) 
    return()

Answer 1

No. The thread will terminate on its own. The join() function is a convenience that tells the parent thread to block until the child thread is finished (so if the child thread hasn't finished yet, then the parent thread won't continue).

You can see evidence of this on the python console (even before I call t.join() , the thread is already dead):

>>> def function1():
...     print("Hello!")
...     return 5
... 
>>> t = threading.Thread(target=function1)
>>> t.start()
Hello!
>>> t.is_alive()
False
>>> t.join()
>>> t.is_alive()
False