Reduce lock usage during EditDistance.GetEditDistance and BKTree.Find (…

…#75610)

* Reduce lock usage during EditDistance.GetEditDistance and BKTree.Find

The SimplePool and ArrayPool classes previously used always locked on Allocate/Free which is showing up in a trace David Kean referred us to. Instead, as the char arrays being allocated are typically quite small, utilize the stack for these temporary char array locations when possible, falling back to heap allocating in the rare occasions where it's not.

src/Workspaces/Core/Portable/FindSymbols/SymbolTree/SymbolTreeInfo_Source.cs

@@ -16,7 +16,7 @@ namespace Microsoft.CodeAnalysis.FindSymbols;
 
 internal sealed partial class SymbolTreeInfo
 {
-    private static readonly SimplePool<MultiDictionary<string, INamespaceOrTypeSymbol>> s_symbolMapPool = new(() => []);
+    private static readonly ObjectPool<MultiDictionary<string, INamespaceOrTypeSymbol>> s_symbolMapPool = new(() => []);
 
     private static MultiDictionary<string, INamespaceOrTypeSymbol> AllocateSymbolMap()
         => s_symbolMapPool.Allocate();

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/Utilities/BKTree.cs

@@ -70,25 +70,20 @@ public void Find(ref TemporaryArray<string> result, string value, int? threshold
         if (_nodes.Length == 0)
             return;
 
-        var lowerCaseCharacters = ArrayPool<char>.GetArray(value.Length);
-        try
-        {
-            for (var i = 0; i < value.Length; i++)
-                lowerCaseCharacters[i] = CaseInsensitiveComparison.ToLower(value[i]);
+        Span<char> lowerCaseCharacters = value.Length < 512
+            ? stackalloc char[value.Length]
+            : new char[value.Length];
 
-            threshold ??= WordSimilarityChecker.GetThreshold(value);
-            Lookup(_nodes[0], lowerCaseCharacters, value.Length, threshold.Value, ref result, recursionCount: 0);
-        }
-        finally
-        {
-            ArrayPool<char>.ReleaseArray(lowerCaseCharacters);
-        }
+        for (var i = 0; i < value.Length; i++)
+            lowerCaseCharacters[i] = CaseInsensitiveComparison.ToLower(value[i]);
+
+        threshold ??= WordSimilarityChecker.GetThreshold(value);
+        Lookup(_nodes[0], lowerCaseCharacters, threshold.Value, ref result, recursionCount: 0);
     }
 
     private void Lookup(
         Node currentNode,
-        char[] queryCharacters,
-        int queryLength,
+        Span<char> queryCharacters,
         int threshold,
         ref TemporaryArray<string> result,
         int recursionCount)
@@ -122,7 +117,7 @@ private void Lookup(
         var edgesExist = currentNode.EdgeCount > 0;
         var editDistance = EditDistance.GetEditDistance(
             _concatenatedLowerCaseWords.AsSpan(characterSpan.Start, characterSpan.Length),
-            queryCharacters.AsSpan(0, queryLength),
+            queryCharacters,
             edgesExist ? int.MaxValue : threshold);
 
         // Case 1
@@ -146,7 +141,7 @@ private void Lookup(
                 if (min <= childEditDistance && childEditDistance <= max)
                 {
                     Lookup(_nodes[_edges[i].ChildNodeIndex],
-                        queryCharacters, queryLength, threshold, ref result,
+                        queryCharacters, threshold, ref result,
                         recursionCount + 1);
                 }
             }

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/Utilities/EditDistance.cs

@@ -8,6 +8,7 @@
 using System.Text;
 using System.Threading;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.PooledObjects;
 
 namespace Roslyn.Utilities;
 
@@ -48,9 +49,15 @@ internal readonly struct EditDistance(string text) : IDisposable
     private readonly string _source = text ?? throw new ArgumentNullException(nameof(text));
     private readonly char[] _sourceLowerCaseCharacters = ConvertToLowercaseArray(text);
 
+    private const int PooledArraySize = 512;
+    private static readonly ObjectPool<char[]> s_pool = new ObjectPool<char[]>(() => new char[PooledArraySize]);
+
     private static char[] ConvertToLowercaseArray(string text)
     {
-        var array = ArrayPool<char>.GetArray(text.Length);
+        var array = text.Length <= PooledArraySize
+            ? s_pool.Allocate()
+            : new char[text.Length];
+
         for (var i = 0; i < text.Length; i++)
             array[i] = CaseInsensitiveComparison.ToLower(text[i]);
 
@@ -62,7 +69,10 @@ public void Dispose()
         if (_sourceLowerCaseCharacters == null)
             throw new ObjectDisposedException(nameof(EditDistance));
 
-        ArrayPool<char>.ReleaseArray(_sourceLowerCaseCharacters);
+        // Place properly sized arrays back in the pool. As these only store chars, no need
+        // to clear them out before doing so.
+        if (_sourceLowerCaseCharacters.Length == PooledArraySize)
+            s_pool.Free(_sourceLowerCaseCharacters);
     }
 
     public static int GetEditDistance(string source, string target, int threshold = int.MaxValue)
@@ -71,26 +81,22 @@ public static int GetEditDistance(string source, string target, int threshold =
         return editDistance.GetEditDistance(target, threshold);
     }
 
-    public static int GetEditDistance(char[] source, char[] target, int threshold = int.MaxValue)
-        => GetEditDistance(source.AsSpan(), target.AsSpan(), threshold);
-
     public int GetEditDistance(string target, int threshold = int.MaxValue)
     {
         if (_sourceLowerCaseCharacters == null)
             throw new ObjectDisposedException(nameof(EditDistance));
 
-        var targetLowerCaseCharacters = ConvertToLowercaseArray(target);
-        try
-        {
-            return GetEditDistance(
-                _sourceLowerCaseCharacters.AsSpan(0, _source.Length),
-                targetLowerCaseCharacters.AsSpan(0, target.Length),
-                threshold);
-        }
-        finally
-        {
-            ArrayPool<char>.ReleaseArray(targetLowerCaseCharacters);
-        }
+        Span<char> targetLowerCaseCharacters = target.Length < 512
+            ? stackalloc char[target.Length]
+            : new char[target.Length];
+
+        for (var i = 0; i < target.Length; i++)
+            targetLowerCaseCharacters[i] = CaseInsensitiveComparison.ToLower(target[i]);
+
+        return GetEditDistance(
+            _sourceLowerCaseCharacters.AsSpan(0, _source.Length),
+            targetLowerCaseCharacters,
+            threshold);
     }
 
     private const int MaxMatrixPoolDimension = 64;
@@ -600,60 +606,3 @@ private static void SetValue(int[,] matrix, int i, int j, int val)
         matrix[i + 1, j + 1] = val;
     }
 }
-
-internal sealed class SimplePool<T>(Func<T> allocate) where T : class
-{
-    private readonly object _gate = new();
-    private readonly Stack<T> _values = new();
-
-    public T Allocate()
-    {
-        lock (_gate)
-        {
-            if (_values.Count > 0)
-            {
-                return _values.Pop();
-            }
-
-            return allocate();
-        }
-    }
-
-    public void Free(T value)
-    {
-        lock (_gate)
-        {
-            _values.Push(value);
-        }
-    }
-}
-
-internal static class ArrayPool<T>
-{
-    private const int MaxPooledArraySize = 256;
-
-    // Keep around a few arrays of size 256 that we can use for operations without
-    // causing lots of garbage to be created.  If we do compare items larger than
-    // that, then we will just allocate and release those arrays on demand.
-    private static readonly SimplePool<T[]> s_pool = new(() => new T[MaxPooledArraySize]);
-
-    public static T[] GetArray(int size)
-    {
-        if (size <= MaxPooledArraySize)
-        {
-            var array = s_pool.Allocate();
-            Array.Clear(array, 0, array.Length);
-            return array;
-        }
-
-        return new T[size];
-    }
-
-    public static void ReleaseArray(T[] array)
-    {
-        if (array.Length <= MaxPooledArraySize)
-        {
-            s_pool.Free(array);
-        }
-    }
-}