Send CTRL+C to subprocess tree on Windows

Question

I would like to run arbitrary console-based sub-processes and manage them from a single master process. The console based sub-processes communicate via stdin, stdout and stderr, and if you run them in a genuine console they terminate cleanly when you press CTRL+C. Some of them may in fact be a tree of processes, such as a batch script that runs an executable which may in turn run another executable to do some work. I would like to redirect their standard I/O (for example, so that I can show their output in a GUI window) and in certain circumstances to send them a CTRL+C event so that they will give up and terminate cleanly.

The following two diagrams show first the normal structure - one master process has four worker sub-processes, and some of those workers have their own subprocesses; and then what should happen when one of the workers needs to be stopped - it and all of its children should get the CTRL+C event, but no other processes should receive the CTRL+C event.

_{(source: livejournal.com)}

Additionally, I would much prefer that there are no extra windows visible to the user.

Here's what I've tried (note that I'm working in Python, but solutions for C would still be helpful):

• Spawning an extra intermediate process with CREATE_NEW_CONSOLE, and then having it spawn the worker process. Then have it call GenerateConsoleCtrlEvent(CTRL_C_EVENT, 0) when we want to kill the worker. Unfortunately, CREATE_NEW_CONSOLE seems to prevent me from redirecting the standard I/O channels, so I'm left with no easy way to get the output back to the main program.
• Spawning an extra intermediate process with CREATE_NEW_PROCESS_GROUP, and then having it spawn the worker process. Then have it call GenerateConsoleCtrlEvent(CTRL_C_EVENT, 0) when we want to kill the worker. Somehow, this manages to send the CTRL+C only to the master process, which is completely useless. On closer inspection, GenerateConsoleCtrlEvent says that CTRL+C cannot be sent to process groups.
• Spawning the subprocess with CREATE_NEW_PROCESS_GROUP. Then call GenerateConsoleCtrlEvent(CTRL_BREAK_EVENT, pid) to kill the worker. This is not ideal, because CTRL+BREAK is less friendly than CTRL+C and will probably result in a messier termination. (E.g. if it's a Python process, no KeyboardInterrupt can be caught and no finally blocks run.)

Is there any good way to do what I want? I can see that I could theoretically build on the first attempt and find some other way to communicate between the processes, but I am worried it will turn out to be extremely awkward. Are there good examples of other programs that achieve the same effect? It seems so simple that it can't be all that uncommon a requirement.

Answer 1

I don't know about managing/redirecting stdin et. al., but for managing the subprocess tree have you considered using the Windows Job Objects api?

There are several other questions about managing process trees (How do I automatically destroy child processes in Windows? Performing equivalent of “Kill Process Tree” in c++ on windows) and it looks like the cleanest method if you can use it.

Chapter 5 of Windows Via C/C++ by Jeffery Richter has a good discussion on using CreateJobObject and the related APIs.