[raiguard][2.0.20] Connecting fusion generators' output back into fusion reactors sometimes results in plasma loss

[AbyssMage]

As discussed in further comments in this thread, when a fusion power setup has generators whose output connects back into the input/output ports of a reactor, plasma can get lost and overall power production gets reduced. Deleting and rebuilding a generator can fix the issue, so the order of operations seems to make a difference.

Attached are an image and two blueprint strings (with infinity chests and pipes, since this was done in the map editor) which demonstrate the issue - one working setup with one reactor and two generators, which generates the expected 100 MW in all cases, and one broken setup where a generator is shifted slightly to connect one of its outputs back to the reactor. When the broken blueprint is first placed, only one generator receives plasma, as shown in the image provided. If either of the two generators is deleted and rebuilt (but not both at once), they both start receiving plasma. If both generators are deleted and rebuilt simultaneously, it seems to break again.

I've also attached a log file as the reporting instructions requested, though I don't expect anything in there will help diagnose the issue thanks in advance!

Ref.: 123980 127422

[malacai17]

+1 to the odd behavior noted in this post and 123980
I have a 2 reactor / 8 generator setup, and was noticing only 1 reactor working at any given time. None of my generators "feed back" into the reactors.
The non-working reactor ("Output Full" message) was reporting the neighborhood bonus, but the working reactor was not.
I tried removing and rebuilding the reactors, but that didn't change anything.
I then, however, removed one generator (randomly picked one) and put it back into the same spot.
When I placed the generator, both reactors starting producing plasma, notating the neighbor bonus, etc.

[adam_bise]

Same issue on 20.23 Seems like circular plasma paths are not handled properly.

[synchromach]

Same issue here on space platforms (version 2.0.32).

[akado]

I have a similar issue. Using a setup with two fusion reactors on a space platform, currently in the sandbox in [2.0.32]. Although I think I properly connected all the generators not to loop plasma and I even tried to connect the generators using the fluoroketone connections (I tried both variants, connecting the plasma ports of the reactors or the fluoroketone ports, both result in similar behaviour). The neighbour bonus fluctuates wildly and I sometimes see "output full" for a short moment when hovering over the reactor with the mouse.

The setup initially appeared to work just fine, until I quickly switched to nauvis to try something else. After switching the view back to the space platform, I noticed the error again...

01-26-2025, 20-35-52.png (2.83 MiB) Viewed 1075 times

[Omzig]

Here is my workaround till they get it fixed:
viewtopic.php?p=665429#p665429

[raiguard]

I know what the issue is, but fixing it is not straightforward. This is an entity update order issue.

In these pictures, the numbers represent the update order of the fluid buffers:

Broken

03-13-2025, 13-49-10.png (1.69 MiB) Viewed 222 times

Working

03-13-2025, 13-49-29.png (1.69 MiB) Viewed 222 times

In the broken case, the horizontal fusion generator is first emptying its buffer into the fusion reactor, then pulling all of the plasma from the vertical generator. Since the vertical generator updated first, it is now devoid of fluid and can't do anything on that tick. Rinse and repeat ad nauseum.

In the working case, the vertical generator updates after the horizontal generator, so it is able to pull fluid from the reactor and have fluid available on the tick.

[raiguard]

Thanks for the report, this has been fixed for 2.0.42.