replace MemoryCache with custom cache

This was causing significant frame stutters for some players since the migration to .NET 5 in Stardew Valley 1.5.5.

1 files changed, 57 insertions, 0 deletions

diff --git a/src/SMAPI/Framework/Utilities/IntervalMemoryCache.cs b/src/SMAPI/Framework/Utilities/IntervalMemoryCache.cs
new file mode 100644
index 00000000..d2b69f51
--- /dev/null
+++ b/src/SMAPI/Framework/Utilities/IntervalMemoryCache.cs
@@ -0,0 +1,57 @@
+using System;
+using System.Collections.Generic;
+
+namespace StardewModdingAPI.Framework.Utilities
+{
+    /// <summary>A memory cache with sliding expiry based on custom intervals, with no background processing.</summary>
+    /// <typeparam name="TKey">The cache key type.</typeparam>
+    /// <typeparam name="TValue">The cache value type.</typeparam>
+    /// <remarks>This is optimized for small caches that are reset relatively rarely. Each cache entry is marked as hot (accessed since the interval started) or stale.
+    /// When a new interval is started, stale entries are cleared and hot entries become stale.</remarks>
+    internal class IntervalMemoryCache<TKey, TValue>
+        where TKey : notnull
+    {
+        /*********
+        ** Fields
+        *********/
+        /// <summary>The cached values that were accessed during the current interval.</summary>
+        private Dictionary<TKey, TValue> HotCache = new();
+
+        /// <summary>The cached values that will expire on the next interval.</summary>
+        private Dictionary<TKey, TValue> StaleCache = new();
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Get a value from the cache, fetching it first if needed.</summary>
+        /// <param name="cacheKey">The unique key for the cached value.</param>
+        /// <param name="get">Get the latest data if it's not in the cache yet.</param>
+        public TValue GetOrSet(TKey cacheKey, Func<TValue> get)
+        {
+            // from hot cache
+            if (this.HotCache.TryGetValue(cacheKey, out TValue? value))
+                return value;
+
+            // from stale cache
+            if (this.StaleCache.TryGetValue(cacheKey, out value))
+            {
+                this.HotCache[cacheKey] = value;
+                return value;
+            }
+
+            // new value
+            value = get();
+            this.HotCache[cacheKey] = value;
+            return value;
+        }
+
+        /// <summary>Start a new cache interval, removing any stale entries.</summary>
+        public void StartNewInterval()
+        {
+            this.StaleCache.Clear();
+            if (this.HotCache.Count is not 0)
+                (this.StaleCache, this.HotCache) = (this.HotCache, this.StaleCache); // swap hot cache to stale
+        }
+    }
+}