Better AI reachable cleanup (#1507)

Haven't profiled so can't say if it definitely fixes the leak.

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Server/GameObjects/EntitySystems/AI/Pathfinding/Accessible/AiReachableSystem.cs

@@ -75,6 +75,8 @@ namespace Content.Server.GameObjects.EntitySystems.AI.Pathfinding.Accessible
         private Dictionary<ReachableArgs, Dictionary<PathfindingRegion, (TimeSpan CacheTime, HashSet<PathfindingRegion> Regions)>> _cachedAccessible =
             new Dictionary<ReachableArgs, Dictionary<PathfindingRegion, (TimeSpan, HashSet<PathfindingRegion>)>>();
         
+        private readonly List<PathfindingRegion> _queuedCacheDeletions = new List<PathfindingRegion>();
+
 #if DEBUG
         private int _runningCacheIdx = 0;
 #endif
@@ -115,6 +117,13 @@ namespace Content.Server.GameObjects.EntitySystems.AI.Pathfinding.Accessible
             }
 #endif
             _queuedUpdates.Clear();
+
+            foreach (var region in _queuedCacheDeletions)
+            {
+                ClearCache(region);
+            }
+            
+            _queuedCacheDeletions.Clear();
         }
 
         public override void Shutdown()
@@ -123,6 +132,7 @@ namespace Content.Server.GameObjects.EntitySystems.AI.Pathfinding.Accessible
             _queuedUpdates.Clear();
             _regions.Clear();
             _cachedAccessible.Clear();
+            _queuedCacheDeletions.Clear();
         }
 
         public void ResettingCleanup()
@@ -130,6 +140,7 @@ namespace Content.Server.GameObjects.EntitySystems.AI.Pathfinding.Accessible
             _queuedUpdates.Clear();
             _regions.Clear();
             _cachedAccessible.Clear();
+            _queuedCacheDeletions.Clear();
         }
 
         private void RecalculateNodeRegions(PathfindingChunkUpdateMessage message)
@@ -216,7 +227,7 @@ namespace Content.Server.GameObjects.EntitySystems.AI.Pathfinding.Accessible
         public HashSet<PathfindingRegion> GetReachableRegions(ReachableArgs reachableArgs, PathfindingRegion region)
         {
             // if we're on a node that's not tracked at all atm then region will be null
-            if (region == null)
+            if (region == null || region.Deleted)
             {
                 return new HashSet<PathfindingRegion>();
             }
@@ -345,7 +356,7 @@ namespace Content.Server.GameObjects.EntitySystems.AI.Pathfinding.Accessible
 
                 foreach (var neighbor in region.Neighbors)
                 {
-                    if (closedSet.Contains(neighbor))
+                    if (closedSet.Contains(neighbor) || neighbor.Deleted)
                     {
                         continue;
                     }
@@ -530,6 +541,9 @@ namespace Content.Server.GameObjects.EntitySystems.AI.Pathfinding.Accessible
             }
 
             source.Shutdown();
+            // This doesn't check the cachedaccessible to see if it's reachable but maybe it should?
+            // Although currently merge gets spammed so maybe when some other stuff is improved
+            // MergeInto is also only called by GenerateRegions currently so nothing should hold onto the original region
             _regions[source.ParentChunk.GridId][source.ParentChunk].Remove(source);
 
             foreach (var node in target.Nodes)
@@ -538,6 +552,40 @@ namespace Content.Server.GameObjects.EntitySystems.AI.Pathfinding.Accessible
             }
         }
 
+        /// <summary>
+        /// Remove the cached accessibility lookup for this region
+        /// </summary>
+        /// <param name="region"></param>
+        private void ClearCache(PathfindingRegion region)
+        {
+            // Need to forcibly clear cache for ourself and anything that includes us
+            foreach (var (_, cachedRegions) in _cachedAccessible)
+            {
+                if (cachedRegions.ContainsKey(region))
+                {
+                    cachedRegions.Remove(region);
+                }
+
+                // Seemed like the safest way to remove this
+                // We could just have GetVisionAccessible remove us if it can tell we're deleted but that
+                // seems like it could be unreliable
+                var regionsToClear = new List<PathfindingRegion>();
+                        
+                foreach (var (otherRegion, cache) in cachedRegions)
+                {
+                    if (cache.Regions.Contains(region))
+                    {
+                        regionsToClear.Add(otherRegion);
+                    }
+                }
+
+                foreach (var otherRegion in regionsToClear)
+                {
+                    cachedRegions.Remove(otherRegion);
+                }
+            }
+        }
+
         /// <summary>
         /// Generate all of the regions within a chunk
         /// </summary>
@@ -554,8 +602,10 @@ namespace Content.Server.GameObjects.EntitySystems.AI.Pathfinding.Accessible
             {
                 foreach (var region in regions)
                 {
+                    _queuedCacheDeletions.Add(region);
                     region.Shutdown();
                 }
+                
                 _regions[chunk.GridId].Remove(chunk);
             }
 

Content.Server/GameObjects/EntitySystems/AI/Pathfinding/Accessible/PathfindingRegion.cs

@@ -36,6 +36,8 @@ namespace Content.Server.GameObjects.EntitySystems.AI.Pathfinding.Accessible
         public HashSet<PathfindingNode> Nodes => _nodes;
         private HashSet<PathfindingNode> _nodes;
 
+        public bool Deleted { get; private set; }
+
         public PathfindingRegion(PathfindingNode originNode, HashSet<PathfindingNode> nodes, bool isDoor = false)
         {
             OriginNode = originNode;
@@ -53,6 +55,8 @@ namespace Content.Server.GameObjects.EntitySystems.AI.Pathfinding.Accessible
                 var neighbor = neighbors[i];
                 neighbor.Neighbors.Remove(this);
             }
+
+            Deleted = true;
         }
 
         /// <summary>