我正在使用Python 3.7.4的线程功能,并希望使用atexit
来注册一个清理函数,以(干净地)终止这些线程。
例如:
# example.py
import threading
import queue
import atexit
import sys
Terminate = object()
class Worker(threading.Thread):
def __init__(self):
super().__init__()
self.queue = queue.Queue()
def send_message(self, m):
self.queue.put_nowait(m)
def run(self):
while True:
m = self.queue.get()
if m is Terminate:
break
else:
print("Received message: ", m)
def shutdown_threads(threads):
for t in threads:
print(f"Terminating thread {t}")
t.send_message(Terminate)
for t in threads:
print(f"Joining on thread {t}")
t.join()
else:
print("All threads terminated")
if __name__ == "__main__":
threads = [
Worker()
for _ in range(5)
]
atexit.register(shutdown_threads, threads)
for t in threads:
t.start()
for t in threads:
t.send_message("Hello")
#t.send_message(Terminate)
sys.exit(0)
然而,似乎在atexit
回调中与线程和队列交互会导致某些内部关闭例程死锁:
$ python example.py
Received message: Hello
Received message: Hello
Received message: Hello
Received message: Hello
Received message: Hello
^CException ignored in: <module 'threading' from '/usr/lib64/python3.7/threading.py'>
Traceback (most recent call last):
File "/usr/lib64/python3.7/threading.py", line 1308, in _shutdown
lock.acquire()
KeyboardInterrupt
Terminating thread <Worker(Thread-1, started 140612492904192)>
Terminating thread <Worker(Thread-2, started 140612484511488)>
Terminating thread <Worker(Thread-3, started 140612476118784)>
Terminating thread <Worker(Thread-4, started 140612263212800)>
Terminating thread <Worker(Thread-5, started 140612254820096)>
Joining on thread <Worker(Thread-1, stopped 140612492904192)>
Joining on thread <Worker(Thread-2, stopped 140612484511488)>
Joining on thread <Worker(Thread-3, stopped 140612476118784)>
Joining on thread <Worker(Thread-4, stopped 140612263212800)>
Joining on thread <Worker(Thread-5, stopped 140612254820096)>
All threads terminated
(KeyboardInterrupt
是我使用 ctrl-c
的方式,因为该进程似乎无限期挂起)。
然而,在退出之前发送 Terminate
消息(取消注释 t.send_message("Hello")
后的那行),程序不会挂起,而是正常终止:
$ python example.py
Received message: Hello
Received message: Hello
Received message: Hello
Received message: Hello
Received message: Hello
Terminating thread <Worker(Thread-1, stopped 140516051592960)>
Terminating thread <Worker(Thread-2, stopped 140516043200256)>
Terminating thread <Worker(Thread-3, stopped 140515961992960)>
Terminating thread <Worker(Thread-4, stopped 140515953600256)>
Terminating thread <Worker(Thread-5, stopped 140515945207552)>
Joining on thread <Worker(Thread-1, stopped 140516051592960)>
Joining on thread <Worker(Thread-2, stopped 140516043200256)>
Joining on thread <Worker(Thread-3, stopped 140515961992960)>
Joining on thread <Worker(Thread-4, stopped 140515953600256)>
Joining on thread <Worker(Thread-5, stopped 140515945207552)>
All threads terminated
这引出了一个问题,
threading._shutdown
例程相对于atexit
处理程序何时执行?
在atexit
处理程序中与线程交互是否有意义?
#t.send_message(Terminate)
呢? - stovflatexit
处理程序,这听起来很可疑,就像在Python 2.6.5中修复的错误一样(请参见-https://dev59.com/qFDTa4cB1Zd3GeqPJXmE和https://bugs.python.org/issue1722344)。解决方法可能是将主代码包装在`try` /finally
中,并手动调用shutdown_threads(threads)
。 - martineau