Use Job Objects and equivalent things on Mac/Linux

[egonelbre]

Currently when starting things with watchrun go run main.go and main.go contains a server, then watchrun doesn't automatically kill the subprocess. Which is not ideal. We can overcome this limitation by monitoring which subprocesses are created and then ensure they are killed as a whole.

On Windows there are Job Objects, which allow such process groups that can be killed as a whole. The current approach for killing processes in Windows is rather hacky https://github.com/loov/watchrun/blob/master/pgroup/kill_windows.go#L19.

I'm not sure what the best approach on Unix is, but may be monitoring things with ptrace and capturing the pids?

[egonelbre]

@gedw99 note, I'm that approach, but it doesn't seem to be sufficient. (https://github.com/loov/watchrun/blob/master/pgroup/kill_windows.go#L13)

[egonelbre]

The issue is with subprocesses starting processes themselves and not chaining to the process group properly, so when you try to kill the process group the children won't be shutdown. Similarly, killing by PID can be problematic, because at the point of trying to kill, some other process may have started with the same PID (although, it's very unlikely). Similarly sending kill signal is notoriously in-effective on Windows, because processes can disregard that message.

[egonelbre]

Kind of. It's more of, the default process group / tree in Windows doesn't fully contain the children. i.e. it allows to detach subprocesses, so killing the tree doesn't kill them. But, yes, AFAIK, if they properly handle the process grouping themselves, then there should be less issues.

[egonelbre]

Well, that seems more work than getting job objects etc. similar working.

[egonelbre]

https://learn.microsoft.com/en-us/windows/win32/procthread/job-objects

[egonelbre]

The objective isn't monitoring, it's just to ensure that the process and all sub-processes get shutdown.

And, yes, I'm aware that there are packages that implement winjob api. For Windows, I'll probably use https://pkg.go.dev/golang.org/x/sys/windows directly. Watchrun needs a small set of features, so directly using winapi should be sufficient.