[PATCH] when agent is null

This topic has 0 replies, 2 voices, and was last updated 5 years, 7 months ago by Gavalakis.

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September 22, 2020 at 2:32 pm #16113

hosnkobf

Participant

Hi,

I am up-using node canvas for our strategy game. The characters get different graphs assigned by code at certain events.

sometimes characters are destroyed. Probably my code is buggy because it seems like destroyed characters sometimes also get a graph assigned. Then the agent is “null” and for some reason all newly assigned graphs for existing characters are stuck in the first node.

I refactored my code a bit and maybe fixed the problem there (couldn’t reproduce it yet). But I also patched ActionTask.Execute() just to be more safe:

public Status Execute(Component agent, IBlackboard blackboard) {

// PATCH START

if (agent == null) {

return Status.Error;

}

// PATCH END

if ( !isUserEnabled )

// ...

I guess it would be a good idea to apply my patch to your repository.

September 29, 2020 at 12:56 pm #16116

Gavalakis

Keymaster

Hello,

Hmm. Within this same method (Execute), there is this piece of code:

if ( !Set(agent, blackboard) ) {

latch = false;

return Status.Failure;

}

The above code, is basically handling the agent null check but also initializes the agent. The reason this piece of code is not at the very top, is so that the checks and initialization only happen when the action is executed initially (and not every time while it is running).
It seems however that in your case, the agent is destroyed while the action in question is Running or paused?
Are you maybe destroying the agent from within an action task, or is destruction happening from some outside piece of code?

Please let me know.
Thank you.

September 29, 2020 at 1:57 pm #16115

hosnkobf

Participant

Hi,

When I am destroying a character I call in OnDestroy() _currentActivityGraph?.Stop(); This should be enough to abort the graph, I guess.

However, I got the null-ref-exception at OnUpdate() before your quoted check is executed:

isPaused = false;

if ( status == Status.Running ) {

OnUpdate(); // <<< here (line 74 or so without patch applied)

latch = false;

return status;

}

It was not clear how to reproduce it. So, I am not quiete sure what caused the graph to get there. If I find out more, I will let you know.

October 8, 2020 at 2:51 am #16114

Gavalakis

Keymaster

Hello again and thanks for the follow up as well as the information.
I will try to reproduce this and I make the required changes to avoid this null reference. (probably implementing your fix as well).
Thank you 🙂

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