Issue #1183: implement ppid_map for Linux

[pitrou]

This makes Process.children() 3x faster when there are no children.

[pitrou]

Note that Process.children(recursive=True) doesn't really benefit as it still creates a Process instance for every process on the system.

[pitrou]

@giampaolo

[pitrou]

I've got a patch to also make children(recursive=True) faster. Should I push it in this PR or create a separate PR for it?

[giampaolo]

That won't work as it's Linux only. The change is much simpler: just define a _ppid_map() utility function in __init__.py which relies on the per-module Process class directly. That way all platforms can benefit from the speedup.

[pitrou]

The change is much simpler: just define a _ppid_map() utility function in init.py which relies on the per-module Process class directly.

Not sure what you mean by that? The point here is to avoid Process instantiations when we're only interested in a couple of them at the end.

[giampaolo]

Instantiating "private" (e.g. look into _pslinux.py) Process classes should be cheap as they define __slots__ (contrarily from the Process class in __init__).

[giampaolo]

#1185

[giampaolo]

Super seeded by #1185.