Introduce MoveCooldownHelper to prevent lag spikes from failed pathfinding #21391
Conversation
…nding Several activities that queue child Move activities can get into a bad scenario where the actor is pathfinding and then gets stuck because the destination is unreachable. When the Move activity then completes, then parent activity sees it has yet to reach the destination and tries to move again. However, the actor is still blocked in the same spot as before and thus the movment finishes immediately. This causes a performance death spiral where the actor attempts to pathfind every tick. The pathfinding attempt can also be very expensive if it must exhaustively check the whole map to determine no route is possible. In order to prevent blocked actors from running into this scenario, we introduce MoveCooldownHelper. In its default setup it allows the parent activity to bail out if the actor was blocked during a pathfinding attempt. This means the activity will be dropped rather than trying to move endlessly. It also has an option to allow retrying if pathfinding was blocked, but applies a cooldown to avoid the performance penalty. For activities such as Enter, this means the actors will still try and enter their target if it is unreachable, but will only attempt once a second now rather than every tick.
There was a problem hiding this comment.
Hervester still queues move every tick. As for minelayer, I recon it should be among those units that repeatedly tries to queue move.
This also feels incorrect for handling multiple queued orders / layered orders. One example I found that if I guard a unit in an unreachable position, then killing the guarded units doesn't stop the activity. The only way to end it is to manually stop it or make the position reachable
|
In the world of web they use the term |
|
it might be worth to cancel harvesting when unable to reach the destination and try to pick a new location. FindAndDeliverResources already handles failed searches, the code just needs to propagate the unreachable error from HarvestResource |
Several activities that queue child Move activities can get into a bad scenario where the actor is pathfinding and then gets stuck because the destination is unreachable. When the Move activity then completes, then parent activity sees it has yet to reach the destination and tries to move again. However, the actor is still blocked in the same spot as before and thus the movment finishes immediately. This causes a performance death spiral where the actor attempts to pathfind every tick. The pathfinding attempt can also be very expensive if it must exhaustively check the whole map to determine no route is possible.
In order to prevent blocked actors from running into this scenario, we introduce MoveCooldownHelper. In its default setup it allows the parent activity to bail out if the actor was blocked during a pathfinding attempt. This means the activity will be dropped rather than trying to move endlessly. It also has an option to allow retrying if pathfinding was blocked, but applies a cooldown to avoid the performance penalty. For activities such as Enter, this means the actors will still try and enter their target if it is unreachable, but will only attempt once a second now rather than every tick.
Based on and supersedes #20954. Fixes #21187, #21203.
#21164 means that the test case from #21187 no longer has easily visible impact. The repeated pathfinding attempts every tick are there, but they're very cheap now.
I recommend the test case from #21203 instead. This doesn't benefit from the changes in #21164 and the performance impact is very obvious.
Bleed:
Attack moving with units trapped in by a laser fence causes the game to slow to a crawl for a long time.
PR:
Attack moving with units trapped in by a laser fence causes an initial lag spike, but after that the performance is reasonable.