minor optimizations in watcher code

Author: Pathoschild

docs/release-notes.md

@@ -5,6 +5,7 @@
 * For players:
   * The installer now deletes obsolete files from very old SMAPI versions again. (This was removed in SMAPI 4.0, but many players still had very old versions.)
   * The installer now deletes Error Handler automatically if it's at the default path.
+  * Minor optimizations.
   * Updated mod compatibility list.
 
 * For mod authors:

src/SMAPI/Framework/StateTracking/ChestTracker.cs

@@ -74,7 +74,9 @@ public void Update()
         public void Reset()
         {
             // update stack sizes
-            foreach (Item item in this.StackSizes.Keys.ToArray().Concat(this.Added))
+            foreach (Item item in this.StackSizes.Keys)
+                this.StackSizes[item] = item.Stack;
+            foreach (Item item in this.Added)
                 this.StackSizes[item] = item.Stack;
 
             // update watcher

src/SMAPI/Framework/StateTracking/Snapshots/WorldLocationsSnapshot.cs

@@ -1,5 +1,4 @@
 using System.Collections.Generic;
-using System.Linq;
 using StardewModdingAPI.Framework.StateTracking.Comparers;
 using StardewValley;
 
@@ -14,6 +13,9 @@ internal class WorldLocationsSnapshot
         /// <summary>A map of tracked locations.</summary>
         private readonly Dictionary<GameLocation, LocationSnapshot> LocationsDict = new(new ObjectReferenceComparer<GameLocation>());
 
+        /// <summary>The pooled list instance for <see cref="GetMissingLocations"/>.</summary>
+        private static readonly List<GameLocation> PooledMissingLocations = new();
+
 
         /*********
         ** Accessors
@@ -36,7 +38,7 @@ public void Update(WorldLocationsTracker watcher)
             this.LocationList.Update(watcher.IsLocationListChanged, watcher.Added, watcher.Removed);
 
             // remove missing locations
-            foreach (var key in this.LocationsDict.Keys.Where(key => !watcher.HasLocationTracker(key)).ToArray())
+            foreach (var key in this.GetMissingLocations(watcher))
                 this.LocationsDict.Remove(key);
 
             // update locations
@@ -48,5 +50,26 @@ public void Update(WorldLocationsTracker watcher)
                 snapshot.Update(locationWatcher);
             }
         }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Get the watched locations which no longer exist in the world, if any.</summary>
+        /// <param name="watcher">The location list tracker.</param>
+        private List<GameLocation> GetMissingLocations(WorldLocationsTracker watcher)
+        {
+            List<GameLocation> list = WorldLocationsSnapshot.PooledMissingLocations;
+            if (list.Count > 0)
+                list.Clear();
+
+            foreach (GameLocation location in this.LocationsDict.Keys)
+            {
+                if (!watcher.HasLocationTracker(location))
+                    list.Add(location);
+            }
+
+            return list;
+        }
     }
 }

src/SMAPI/Framework/StateTracking/WorldLocationsTracker.cs

@@ -30,6 +30,9 @@ internal class WorldLocationsTracker : IWatcher
         /// <summary>A lookup of registered buildings and their indoor location.</summary>
         private readonly Dictionary<Building, GameLocation?> BuildingIndoors = new(new ObjectReferenceComparer<Building>());
 
+        /// <summary>The pooled list instance for <see cref="GetLocationsWhoseBuildingsChanged"/>.</summary>
+        private static readonly List<LocationTracker> PooledLocationsWithBuildingsChanged = new();
+
 
         /*********
         ** Accessors
@@ -95,7 +98,7 @@ public void Update()
             }
 
             // detect building changed
-            foreach (LocationTracker watcher in this.Locations.Where(p => p.BuildingsWatcher.IsChanged).ToArray())
+            foreach (LocationTracker watcher in this.GetLocationsWhoseBuildingsChanged())
             {
                 this.Remove(watcher.BuildingsWatcher.Removed);
                 this.Add(watcher.BuildingsWatcher.Added);
@@ -261,5 +264,21 @@ private IEnumerable<IWatcher> GetWatchers()
             foreach (LocationTracker watcher in this.Locations)
                 yield return watcher;
         }
+
+        /// <summary>Get the locations whose building list changed, if any.</summary>
+        private List<LocationTracker> GetLocationsWhoseBuildingsChanged()
+        {
+            List<LocationTracker> list = WorldLocationsTracker.PooledLocationsWithBuildingsChanged;
+            if (list.Count > 0)
+                list.Clear();
+
+            foreach (LocationTracker watcher in this.LocationDict.Values)
+            {
+                if (watcher.IsChanged)
+                    list.Add(watcher);
+            }
+
+            return list;
+        }
     }
 }