Python 线程在 Python 中使用 ctrl-c 退出

Question

我有如下 Python 多线程程序。如果我在 5 秒（大约）内按 ctrl+c，它将进入 KeyboardInterrupt 异常。

运行代码超过 15 秒无法响应 ctrl+c。 如果我在 15 秒后按 ctrl+c，它不起作用。它不会抛出 KeyboardInterrupt 异常。可能是什么原因 ？我在 Linux 上对此进行了测试。

#!/usr/bin/python

import os, sys, threading, time

class Worker(threading.Thread):
  def __init__(self):
    threading.Thread.__init__(self)
    # A flag to notify the thread that it should finish up and exit
    self.kill_received = False

  def run(self):
      while not self.kill_received:
          self.do_something()

  def do_something(self):
      [i*i for i in range(10000)]
      time.sleep(1)

def main(args):

    threads = []
    for i in range(10):
        t = Worker()
        threads.append(t)
        t.start()

    while len(threads) > 0:
        try:
            # Join all threads using a timeout so it doesn't block
            # Filter out threads which have been joined or are None
            threads = [t.join(1) for t in threads if t is not None and t.isAlive()]
        except KeyboardInterrupt:
            print "Ctrl-c received! Sending kill to threads..."
            for t in threads:
                t.kill_received = True

if __name__ == '__main__':
  main(sys.argv)

Answer 1

第一次执行后

threads = [t.join(1) for t in threads if t is not None and t.isAlive()]

您的变量 threads 包含

[None, None, None, None, None, None, None, None, None, None]

第二次执行后，同样的变量threads包含：

[]

此时，len(threads) > 0 为 False，您将退出 while 循环。您的脚本仍在运行，因为您有 10 个线程仍然处于活动状态，但是由于您不再在 try / except 块中（以捕获 KeyboardInterrupt），因此您无法停止使用 Ctrl + C

在您的脚本中添加一些打印以查看我所描述的内容：

#!/usr/bin/python

import os, sys, threading, time

class Worker(threading.Thread):
  def __init__(self):
    threading.Thread.__init__(self)
    # A flag to notify the thread that it should finish up and exit
    self.kill_received = False

  def run(self):
      while not self.kill_received:
          self.do_something()

  def do_something(self):
      [i*i for i in range(10000)]
      time.sleep(1)

def main(args):

    threads = []
    for i in range(10):
        t = Worker()
        threads.append(t)
        t.start()
        print('thread {} started'.format(i))

    while len(threads) > 0:
        print('Before joining')
        try:
            # Join all threads using a timeout so it doesn't block
            # Filter out threads which have been joined or are None
            threads = [t.join(1) for t in threads if t is not None and t.isAlive()]
            print('After join() on threads: threads={}'.format(threads))

        except KeyboardInterrupt:
            print("Ctrl-c received! Sending kill to threads...")
            for t in threads:
                t.kill_received = True
    print('main() execution is now finished...')

if __name__ == '__main__':
  main(sys.argv)

结果：

$ python thread_test.py
thread 0 started
thread 1 started
thread 2 started
thread 3 started
thread 4 started
thread 5 started
thread 6 started
thread 7 started
thread 8 started
thread 9 started
Before joining
After join() on threads: threads=[None, None, None, None, None, None, None, None, None, None]
Before joining
After join() on threads: threads=[]
main() execution is now finished...

其实 Ctrl + C 不会在 15 秒后停止工作，而是在 10 或 11 秒后停止工作。这是创建和启动 10 个线程（不到一秒）以及在每个线程上执行 join(1) 所需的时间（大约 10 秒）。

来自the doc的提示：

由于join()总是返回None，你必须在join()之后调用isAlive()来判断是否超时——如果线程还活着，join()调用就超时了。

Answer 2

为了跟进上面的海报，isAlive() 被重命名为 is_alive() 在 Python 3.9.6 上尝试过

完整代码：

#!/usr/bin/python

import os, sys, threading, time

class Worker(threading.Thread):
  def __init__(self):
    threading.Thread.__init__(self)
    # A flag to notify the thread that it should finish up and exit
    self.kill_received = False

  def run(self):
      while not self.kill_received:
          self.do_something()

  def do_something(self):
      [i*i for i in range(10000)]
      time.sleep(1)

def main(args):

    threads = []
    for i in range(10):
        t = Worker()
        threads.append(t)
        t.start()
        print('thread {} started'.format(i))

    while len(threads) > 0:
        print('Before joining')
        try:
            # Join all threads using a timeout so it doesn't block
            # Filter out threads which have been joined or are None
            threads = [t.join(1) for t in threads if t is not None and t.is_alive()]
            print('After join() on threads: threads={}'.format(threads))

        except KeyboardInterrupt:
            print("Ctrl-c received! Sending kill to threads...")
            for t in threads:
                t.kill_received = True
    print('main() execution is now finished...')

if __name__ == '__main__':
  main(sys.argv)