openSUSE / agama / 7356884920

72%

push

github

Avoid a deadlock updating the network D-Bus tree (#966)

## Problem

If the network service receives an `Apply` at the same time as any other
request, it may get blocked.

## Solution

Updating the tree must be done in a separate task. Otherwise, it could
fight with an incoming request for the ObjectServer mutex, blocking the
actions dispatching.

## Using tokio-console

I decided to use
[tokio-console](https://docs.rs/tokio-console/latest/tokio_console/) to
make it easier to find the problem. This tool collects and displays
information about the asynchronous tasks in your program. In the
screenshot below you can see that the D-Bus `Set` dispatchers are
blocked.

![Captura desde 2023-12-29
10-52-45](https://github.com/openSUSE/agama/assets/15836/648e5f1e-eb6b-431b-be40-45cdeaf9e980)

Once you find the problem, it is kind of "obvious", but it may take some
time until you figure out what is happening.

To use `tokio-console` you need to add some instrumentation to your
program and, at this point, it implies adding some unstable Tokio APIs.
So if you want to give it a try, you can try the code in the
[tokio-console
branch](https://github.com/openSUSE/agama/compare/tokio-console).

1426 of 2171 branches covered (0.0%)

Branch coverage included in aggregate %.

16064 of 21150 relevant lines covered (75.95%)

22.61 hits per line