Add new benchmark for reusing record type and fix boxing

- This PR adds a new benchmark that reuses the record type to reduce
  allocations.
- This fix caches a boxed true and false value on the heap and returns
  the boxed value instead of reboxing each time in BooleanCovnerter.
  This saves on allocations and reduces memory presure in the new
  BenchmarkEnumerateRecordsSingleInstance benchmark.

Author: Nik Karpinsky

performance/CsvHelper.Benchmarks/BenchmarkEnumerateRecordsSingleInstance.cs

@@ -0,0 +1,60 @@
+using System;
+using System.Globalization;
+using System.IO;
+using BenchmarkDotNet.Attributes;
+
+namespace CsvHelper.Benchmarks;
+
+[MemoryDiagnoser]
+public class BenchmarkEnumerateRecordsSingleInstance
+{
+    private const int entryCount = 2000;
+    private readonly MemoryStream stream = new();
+
+    public class SimpleWithValueType
+    {
+        public int Id { get; set; }
+        public bool Flag1 { get; set; }
+        public bool Flag2 { get; set; }
+    }
+
+    [GlobalSetup]
+    public void GlobalSetupSimple()
+    {
+        using var streamWriter = new StreamWriter(this.stream, null, -1, true);
+        using var writer = new CsvWriter(streamWriter, CultureInfo.InvariantCulture, true);
+        var random = new Random(43); // Different seed for variety
+
+        writer.WriteHeader(typeof(SimpleWithValueType));
+        writer.NextRecord();
+        for (int i = 0; i < entryCount; ++i)
+        {
+            writer.WriteRecord(new SimpleWithValueType()
+            {
+                Id = random.Next(),
+                Flag1 = random.Next(2) == 0,
+                Flag2 = random.Next(2) == 0
+            });
+            writer.NextRecord();
+        }
+    }
+
+    [GlobalCleanup]
+    public void GlobalCleanupSimple()
+    {
+        this.stream.Dispose();
+    }
+
+    [Benchmark]
+    public void EnumerateRecordsSingleInstance()
+    {
+        this.stream.Position = 0;
+        using var streamReader = new StreamReader(this.stream, null, true, -1, true);
+        using var csv = new CsvReader(streamReader, CultureInfo.InvariantCulture, true);
+        var instance = new SimpleWithValueType();
+        foreach (var record in csv.EnumerateRecords(instance))
+        {
+            _ = record;
+        }
+    }
+}

performance/CsvHelper.Benchmarks/BenchmarkMain.cs

@@ -4,8 +4,8 @@ namespace CsvHelper.Benchmarks;
 
 internal class BenchmarkMain
 {
-	static void Main(string[] args)
-	{
-		_ = BenchmarkRunner.Run<BenchmarkEnumerateRecords>();
-	}
+    static void Main(string[] args)
+    {
+		_ = BenchmarkSwitcher.FromAssembly(System.Reflection.Assembly.GetExecutingAssembly()).Run(args);
+    }
 }

performance/CsvHelper.Benchmarks/CsvHelper.Benchmarks.csproj

@@ -7,6 +7,7 @@
 
   <ItemGroup>
     <PackageReference Include="BenchmarkDotNet" Version="0.15.0" />
+    <PackageReference Include="Microsoft.VisualStudio.DiagnosticsHub.BenchmarkDotNetDiagnosers" Version="18.0.36421.1" />
   </ItemGroup>
 
   <ItemGroup>

src/CsvHelper/TypeConversion/BooleanConverter.cs

@@ -12,59 +12,62 @@ namespace CsvHelper.TypeConversion;
 /// </summary>
 public class BooleanConverter : DefaultTypeConverter
 {
-	/// <inheritdoc/>
-	public override object? ConvertFromString(string? text, IReaderRow row, MemberMapData memberMapData)
-	{
-		if (bool.TryParse(text, out var b))
-		{
-			return b;
-		}
+    private static readonly object BoxedTrue = true;
+    private static readonly object BoxedFalse = false;
 
-		if (short.TryParse(text, out var sh))
-		{
-			if (sh == 0)
-			{
-				return false;
-			}
-			if (sh == 1)
-			{
-				return true;
-			}
-		}
+    /// <inheritdoc/>
+    public override object? ConvertFromString(string? text, IReaderRow row, MemberMapData memberMapData)
+    {
+        if (bool.TryParse(text, out var b))
+        {
+            return b ? BoxedTrue : BoxedFalse;
+        }
 
-		var t = (text ?? string.Empty).Trim();
-		foreach (var trueValue in memberMapData.TypeConverterOptions.BooleanTrueValues)
-		{
-			if (memberMapData.TypeConverterOptions.CultureInfo!.CompareInfo.Compare(trueValue, t, CompareOptions.IgnoreCase) == 0)
-			{
-				return true;
-			}
-		}
+        if (short.TryParse(text, out var sh))
+        {
+            if (sh == 0)
+            {
+                return BoxedFalse;
+            }
+            if (sh == 1)
+            {
+                return BoxedTrue;
+            }
+        }
 
-		foreach (var falseValue in memberMapData.TypeConverterOptions.BooleanFalseValues)
-		{
-			if (memberMapData.TypeConverterOptions.CultureInfo!.CompareInfo.Compare(falseValue, t, CompareOptions.IgnoreCase) == 0)
-			{
-				return false;
-			}
-		}
+        var t = (text ?? string.Empty).Trim();
+        foreach (var trueValue in memberMapData.TypeConverterOptions.BooleanTrueValues)
+        {
+            if (memberMapData.TypeConverterOptions.CultureInfo!.CompareInfo.Compare(trueValue, t, CompareOptions.IgnoreCase) == 0)
+            {
+                return BoxedTrue;
+            }
+        }
 
-		return base.ConvertFromString(text, row, memberMapData);
-	}
+        foreach (var falseValue in memberMapData.TypeConverterOptions.BooleanFalseValues)
+        {
+            if (memberMapData.TypeConverterOptions.CultureInfo!.CompareInfo.Compare(falseValue, t, CompareOptions.IgnoreCase) == 0)
+            {
+                return BoxedFalse;
+            }
+        }
 
-	/// <inheritdoc/>
-	public override string? ConvertToString(object? value, IWriterRow row, MemberMapData memberMapData)
-	{
+        return base.ConvertFromString(text, row, memberMapData);
+    }
+
+    /// <inheritdoc/>
+    public override string? ConvertToString(object? value, IWriterRow row, MemberMapData memberMapData)
+    {
 		var b = value as bool?;
 		if (b == true && memberMapData.TypeConverterOptions.BooleanTrueValues.Count > 0)
-		{
-			return memberMapData.TypeConverterOptions.BooleanTrueValues.First();
-		}
+        {
+            return memberMapData.TypeConverterOptions.BooleanTrueValues.First();
+        }
 		else if (b == false && memberMapData.TypeConverterOptions.BooleanFalseValues.Count > 0)
-		{
-			return memberMapData.TypeConverterOptions.BooleanFalseValues.First();
-		}
+        {
+            return memberMapData.TypeConverterOptions.BooleanFalseValues.First();
+        }
 
-		return base.ConvertToString(value, row, memberMapData);
-	}
+        return base.ConvertToString(value, row, memberMapData);
+    }
 }