[4.7.0] BT Simple Parallel Crashes on empty Selector or Sequence

Development Cinematics & Media
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1

If you connect a MoveTo to the task and a Selector or Sequence without any children to the background tree of a SimpleParallel. Your PIE game will crash as soon as the SimpleParallel is entered.

2

Hi Kylawl,

I have been testing this in 4.7.1 with a simple behavior tree that goes directly into a simple parallel. The simple parallel has a move to as the task and a sequence as the background task. I kept this as simple as possible and I was not able to get a crash. If there are any other details from your setup that may be affecting the outcome, please let me know so I can modify my tests.

Could you please post a screenshot of your behavior tree? Also, can you include your crash callstack that the crash log file (Located in the [Project Name]/Saved/Logs folder)

That information may help with the investigation.

Cheers!

3

Hi ,

I’ve attached a screenshot of my tree and it still occurs in 4.7.2

Also I should clarify that this is not a crash, the game actually just locks up. No asserts, no nothing. It actually looks like an infinite loop.

33498-btlockup.png
33498-btlockup.png683×887 63.2 KB

4

Does HuntTarget have a default value? Based on this, it checks if that is Set before setting it, so it seems like this would fail every time. If you just have it go to the Move To node and skip the simple parallel, does it give the same result?

5

The HuntTarget is set by some underlying logic in c++. I’m actually not even using a simple parallel right now, I was simply testing an idea when I came across this issue.

Something as simple as

Root
    -> SimpleParallel (BlackBoard Decorator - ActorGoal IsSet)
         -> MoveTo ActorGoal
         -> Selector

Where ActorGoal is a BlackBoard value set from your AIController blueprint’s tick function

6

Thank you for that info, I was able to get a repro of the issue. I have good news for you, it appears this is related to the simple parallel not knowing when to finish and has since been fixed. It is marked for being put into the 4.7.3 hotfix integration and I was able to see that it is fixed internally, so even if that deadline is missed it will be fixed very soon. Thank you so much for this report and please let us know if you encounter any other odd behavior.

7

Thanks , will do.