Add plumbing for performing custom activity code on actor disposal #15622

reaperrr · 2018-09-17T01:32:23Z

It appears that if an actor dies (or is disposed directly) while an activity is active, the actor will be disposed before the activities' TickOuter can tick one last time, so OnLastRun is never triggered.
As #15543 shows, this can lead to some nasty bugs.

This PR enforces a proper activity end on actor death/disposal.

pchote · 2018-09-17T02:00:21Z

OpenRA.Game/Activities/Activity.cs

+		/// <summary>
+		/// Used only by Actor.Dispose() to make sure the activity finishes properly on death/disposal of actor
+		/// </summary>
+		public virtual void ForceCancel(Actor self)


I think it would be better to call this OnActorDispose instead, and leave the default implementation doing nothing.

The individual activity subclasses can then choose to override this with their own cleanup logic, avoiding any side-effects that might otherwise happen by blindly calling OnLastRun without knowing what the activities might be doing inside there.

I can do that, but I'm not convinced that OnLastRun being skipped on actor death/disposal is intentional.
Pinging @obrakmann just in case he has time to chime in on this.

Tbh, I didn't quite think of modifying third-party state in the OnLastRun method, so the thought hasn't even crossed my mind. But I do agree with Paul here that unconditionally running OnLastRun might not be such a hot idea, and it should be up the activities themselves to decide what needs cleaning up after an actor gets disposed of.

reaperrr · 2018-09-17T20:08:26Z

Ok, somehow can't get the fix to work anymore no matter what I try, I need to debug that first.

pchote · 2018-09-17T20:09:37Z

My first thought is the need to be careful about parent/child activities.

reaperrr · 2018-09-17T22:17:52Z

Yes, the problem was that ResupplyAircraft chains Repair as ChildActivity.

This PR should be good as-is, I didn't need to make any further changes to this PR's code to fix/work around the problem in #15543 (which I've also updated now, so it serves as testcase).

pchote · 2018-09-17T22:20:30Z

OpenRA.Game/Activities/Activity.cs

 		public virtual bool Cancel(Actor self, bool keepQueue = false)
 		{
+			// Just a safe-guard in case this activity was already successfully cancelled
+			if (IsCanceled)


This will cause problems if you cancel an activity that takes a few ticks to complete (e.g. Move), queue a new activity, and then call Cancel again before the original activity has completed. Expected behaviour: second activity is cancelled, actual behaviour: it won't be.

reaperrr · 2018-09-20T19:28:22Z

Updated.
That Cancel change was only a left-over from my old ForceCancel approach anyway.

pchote · 2018-09-20T19:30:00Z

OpenRA.Game/Actor.cs

+			// If CurrentActivity isn't null, run OnActorDispose in case some cleanups are needed.
+			// This should be done before the FrameEndTask to avoid dependency issues.
+			if (CurrentActivity != null)
+				CurrentActivity.RootActivity.OnActorDispose(this);


Do we need to worry about propagating this to child activities, or do we assume that the activities will handle this themselves if they use them? My gut feeling is that this probably should be automatic.

I lean towards agreeing that it should be automatic, that would require changing the protection level of ChildActivity, though.
Personally I wouldn't really mind, just wanted to point it out in case there are some potential issues with that I'm not aware of.

One option is to define a OnActorDisposeOuter on Activity (it should have internal visibility so that mod code can't see it), which calls OnActorDisposeOuter on the child activity if it exists and then calls OnActorDispose on itself. We use this pattern in other places, notably widgets. We may also want to propagate this through the NextActivity chain too?

If this isn't going to work then I think a reasonable compromise is to add a comment to the default OnActorDispose definition explaining that it must be manually chained through by any activities that use child activities.

Appears to work fine, so I'd like to go with it.

Not sure what you mean with propagating through the NextActivity chain, though?

I suppose calling OnActorDisposeOuter on NextActivity (and that activity will call it on its NextActivity and so on, hence "through the chain").

But do we really want or need that?

When the actor is disposed, NextActivity hasn't even started yet, or it wouldn't be "Next" anymore. I don't see why we would want to run the dispose-specific code on activities that haven't even started yet, since that would mean OnFirstRun hasn't run, either. I'm not even sure if the ctor is run before the activity becomes 'current'.

Leaving changes to NextActivity for the future and opened #15632 instead, as discussed on IRC.

This allows activities to perform necessary cleanups on actor death/disposal, for example by running OnLastRun directly, which would otherwise be skipped when the actor dies or is disposed through other means.

reaperrr · 2018-09-22T13:48:41Z

Updated.

abcdefg30 · 2018-09-24T20:10:35Z

Changelog

pchote reviewed Sep 17, 2018

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reaperrr force-pushed the fix-act-onlastrun branch from d747f13 to a701bdc Compare September 17, 2018 18:53

reaperrr added the PR: Changes requested label Sep 17, 2018

reaperrr removed the PR: Changes requested label Sep 17, 2018

reaperrr mentioned this pull request Sep 17, 2018

Merge repair and rearm anim traits into WithResupplyAnimation #15543

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pchote reviewed Sep 17, 2018

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reaperrr added the PR: Fixup requested label Sep 20, 2018

reaperrr force-pushed the fix-act-onlastrun branch from a701bdc to 39323e3 Compare September 20, 2018 18:56

reaperrr removed the PR: Fixup requested label Sep 20, 2018

pchote reviewed Sep 20, 2018

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reaperrr changed the title ~~Fix Activity.OnLastRun being skipped when actor dies~~ Add plumbing for performing custom activity code on actor disposal Sep 20, 2018

Add OnActorDispose plumbing to Activity

2ec969c

This allows activities to perform necessary cleanups on actor death/disposal, for example by running OnLastRun directly, which would otherwise be skipped when the actor dies or is disposed through other means.

reaperrr mentioned this pull request Sep 22, 2018

Properly cancel/finish Child-/SequenceActivities instead of nulling them #15632

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reaperrr force-pushed the fix-act-onlastrun branch from 39323e3 to 2ec969c Compare September 22, 2018 13:41

abcdefg30 approved these changes Sep 24, 2018

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abcdefg30 merged commit 9bcb754 into OpenRA:bleed Sep 24, 2018

reaperrr deleted the fix-act-onlastrun branch October 26, 2018 19:57

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Add plumbing for performing custom activity code on actor disposal #15622

Add plumbing for performing custom activity code on actor disposal #15622

reaperrr commented Sep 17, 2018

pchote Sep 17, 2018 •

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Add plumbing for performing custom activity code on actor disposal #15622

Add plumbing for performing custom activity code on actor disposal #15622

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reaperrr commented Sep 22, 2018

abcdefg30 commented Sep 24, 2018

pchote Sep 17, 2018 •

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