Evaluate switching from txdbus to other Python DBus package

Description

A problem with using txdbus as the solution to talk to the BlueZ DBus service is that it seems to leak file descriptors somewhere. Right now this is solved by having a store of twisted reactors in the __init__.py of bleak.backends.bluez.

This might be improved by using another package. Candidates to evaluate:

• DBussy: https://github.com/ldo/dbussy
• Jeepney: https://jeepney.readthedocs.io/en/latest/

Pros

• Both are pure python and would reduce the number of dependencies for bleak
• It might resolve the file descriptor problem
• An asyncio-only solution in Linux

Cons

• Twisted (which powers txdbus) is a very stable and efficient package. Replacing it with newer, less tested packages might lead to unexpected problems.

[cspensky]

@hbldh Thank you for the detailed response. Indeed, I agree that Bleak is the of the various attempts that I have worked with, hence my current involvement in this repository. Thank you for all of your work! 🙏

I did start down the gattlib as a Bleak backend path out of curiosity but have since pulled the plug. For interested parties, it does seem to be possible to make it play nicely with async, you can see my branches here: bleak and https://github.com/Allthenticate/gattlib/tree/development. It appears that D-Bus in general is the bottleneck and not the Python code in particular. I ran some tests in pure C vs. the Python version and did not see much difference, unfortunately. The library that I was comparing the speed against was bluepy. However, it appears that are circumventing D-Bus and doing some hacky stuff where they are wrapping a compiled binary with Python to get that speed gain.

The only way I’ve really found to get our CPU usage down is by adding scanning filters or, in our case, acting as a peripheral instead of a central. Thus, I plan to jump on board with bless and help push that forward.

[dlech]

I think I would be in favor of exploring one of the alternatives. I did some work last year to fix some bugs in txdbus. One bug (that fortunately doesn’t affect Bleak) I was not able to fix because it would require changing twisted, but I found it to just be too complicated.

Both of the packages you have listed look good.