How to stop a console process on Windows using Python

Background

• In Python, we use p = subprocess.Popen(cmd) to start a command and call p.terminate() to stop it. But for some commands on Windows, e.g. ping 127.0.0.1 -n 9999 , terminate it will "force stop" it without producing the "ping statistics" in the end. These processes need to be stopped by the CTRL-C event in order to allow them finish some "cleanups" nicely.

Discusses

• There've been lots of discusses around this topic.
• FIXME: fix all links
• See Sending ^C to Python subprocess objects on Windows - Stack Overflow and signals - Can I send a ctrl-C (SIGINT) to an application on Windows? - Stack Overflow for solutions
• Also GenerateConsoleCtrlEvent function - Windows Console | Microsoft Docs and subprocess — Subprocess management — Python 3.9.2 documentation for some official info

Summary

• Two solutions
  • Solution 1, use subprocess.send_signal(signal.CTRL_C_EVENT) and ignore the KeyboardInterrupt exception at the caller side
    • The key is to handle the side effects of the CTRL-C event, a simple solution is to wait in the caller process until child process exited.
    • example code

      Copycopy code to clipboard
      # stop the process
       p.send_signal(signal.CTRL_C_EVENT)

       
       # wait in the caller process to ignore the KeyboardInterrupt
      try:
          # needs to be longer than the time costs that child process requires to exit
          time.sleep(10)
      except KeyboardInterrupt:
          print("Ignored keyboard interrupt")

    • Cons
      • The CTRL-C event is sent to the whole process group, which means if your python main process starts a lot of processes, e.g. started multiple ping -n 9999 commands, cancel either one will result in all processes (which have the same process group and have not ignored the KeyboardInterrupt exception) exited earlier than expected.
    • In short, this is a solution for simple applications, or applications don't have multiple child processes with the same process group at the same time.
  • Solution 2, use some "Windows hacks"
    • The key the to completely avoid CTRL-C message being spread to other processes.
    • Starts a new command, which will free the console, attach to the target console, and fires the CTRL-C event.
    • See example code shared in Sending ^C to Python subprocess objects on Windows - Stack Overflow
    • FIXME: add portal here.

The final solution

• I've created a console-ctrl project python package based on the Solution 2, use some "Windows hacks" above.
• FIXME: add portal here.
• See README for details.