Merge pull request #512 from /issues/498

Fix collision handling in`FixedSizeDictionary`

Author: oformaniuk

source/Handlebars.Test/Collections/FixedSizeDictionaryTests.cs

@@ -15,6 +15,31 @@ static FixedSizeDictionaryTests()
             FixedSizeDictionary = new FixedSizeDictionary<object, object, EqualityComparers.ReferenceEqualityComparer<object>>(15, 17, referenceEqualityComparer);
         }
 
+        [Fact]
+        public void AddOrReplace_Collisions()
+        {
+            var comparer = new CollisionsComparer(new Random().Next());
+            var dictionary = new FixedSizeDictionary<object, object, CollisionsComparer>(16, 7, comparer);
+            for (var i = 0; i < dictionary.Capacity; i++)
+            {
+                dictionary.AddOrReplace(new object(), new object(), out _);
+            }
+        }
+        
+        private readonly struct CollisionsComparer : IEqualityComparer<object>
+        {
+            private readonly int _hash;
+
+            public CollisionsComparer(int hash)
+            {
+                _hash = hash;
+            }
+            
+            public bool Equals(object x, object y) => false;
+
+            public int GetHashCode(object obj) => _hash;
+        }
+
         [Fact]
         public void AddOrReplace()
         {

source/Handlebars/Collections/FixedSizeDictionary.cs

@@ -288,6 +288,7 @@ public void AddOrReplace(in TKey key, in TValue value, out EntryIndex<TKey> inde
 
             ref var entryReference = ref _entries[entry.Index];
             entryIndex = entryReference.Index + 1;
+            var downstreamEntryIndex = entryIndex - 1;
 
             for (; entryIndex < _entries.Length; entryIndex++)
             {
@@ -301,7 +302,10 @@ public void AddOrReplace(in TKey key, in TValue value, out EntryIndex<TKey> inde
                 return;
             }
 
-            entryIndex = (bucketIndex * _bucketMask) - 1;
+            // we've searched all entries in -> direction, now visiting in  <- direction
+            entryIndex = downstreamEntryIndex - 1;
+            // handling special case when `downstreamEntryIndex` can result into value >= _entries.Length
+            if (entryIndex >= _entries.Length) entryIndex = _entries.Length - 1;
             for (; entryIndex >= 0; entryIndex--)
             {
                 entry = _entries[entryIndex];

source/Handlebars/Runtime/AmbientContext.cs

@@ -1,12 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.Runtime.CompilerServices;
-#if !NET451 && !NET452
-using System.Threading;
-#else
-using HandlebarsDotNet.Polyfills;
-#endif
-using HandlebarsDotNet.Collections;
 using HandlebarsDotNet.IO;
 using HandlebarsDotNet.ObjectDescriptors;
 using HandlebarsDotNet.PathStructure;
@@ -16,14 +10,18 @@ namespace HandlebarsDotNet.Runtime
 {
     public sealed class AmbientContext : IDisposable
     {
-        private static readonly InternalObjectPool<AmbientContext, Policy> Pool = new InternalObjectPool<AmbientContext, Policy>(new Policy()); 
+        private static readonly InternalObjectPool<AmbientContext, Policy> Pool = new(new Policy()); 
 
-        private static readonly AsyncLocal<ImmutableStack<AmbientContext>> Local = new AsyncLocal<ImmutableStack<AmbientContext>>();
+        [ThreadStatic]
+        private static Stack<AmbientContext> _local;
+
+        private static Stack<AmbientContext> Local => 
+            _local ??= new Stack<AmbientContext>();
 
         public static AmbientContext Current
         {
             [MethodImpl(MethodImplOptions.AggressiveInlining)]
-            get => Local.Value.Peek();
+            get => Local.Count > 0 ? Local.Peek() : null;
         }
 
         public static AmbientContext Create(
@@ -67,12 +65,9 @@ public static AmbientContext Create(
 
         public static DisposableContainer Use(AmbientContext ambientContext)
         {
-            Local.Value = Local.Value.Push(ambientContext);
+            Local.Push(ambientContext);
 
-            return new DisposableContainer(() =>
-            {
-                Local.Value = Local.Value.Pop(out _);
-            });
+            return new DisposableContainer(() => Local.Pop());
         }
 
         private AmbientContext()
@@ -89,14 +84,11 @@ private AmbientContext()
 
         public ObjectDescriptorFactory ObjectDescriptorFactory { get; private set; }
 
-        public Dictionary<string, object> Bag { get; } = new Dictionary<string, object>();
+        public Dictionary<string, object> Bag { get; } = new();
 
         private struct Policy : IInternalObjectPoolPolicy<AmbientContext>
         {
-            public AmbientContext Create()
-            {
-                return new AmbientContext();
-            }
+            public AmbientContext Create() => new();
 
             public bool Return(AmbientContext item)
             {