Automatically attach to subprocesses when debugging

[anathan]

The debugger attach code seems to be hardwired to support only a single process, which breaks support for debugging applications using the multiprocessing library. Perhaps one fix is to allow manual attachment to the child process?

[int19h]

You can already manually attach to a child process via Debug -> Attach to Process. But we do need to support automatic attaching.

[zooba]

@int19h Worth doing this for 3.0? How hard do you think it'll be?

[int19h]

Adding a command from debugger to VS to attach to a new process is easy enough. It's catching all the various ways of spawning those processes from Python that I think might prove tricky. If most of this is pure Python, we should be able to do the same thing we do with threads, and hijack the class responsible.

[alexpilotti]

The milestone here is set to 3.0 which is already out, is there any update on the timeline for this feature? Thanks!

[zooba]

No timeline (and the milestone was un-set a while ago), but we're very aware of this limitation and want to address it. We have more significant debugger work going on first, though.

[alexpilotti]

Thanks, looking forward for it! Unfortunately since almost every significant Python app relies on multiple processes for parallel workloads (os.fork / multiprocessing, etc), remote debugging is not very useful without this feature.

[int19h]

This is supported in debugpy, but requires cooperation from PTVS to light up. Since this is something that shows up quite a lot in web dev (most frameworks use subprocesses to implement auto-reload), we should take another look at this in triage.

[AdamYoblick]

Need to investigate if VS has the extensibility points needed to light this up.