Fix #498 (#507)

src/DotNetty.Common/Utilities/AttributeKey.cs

@@ -5,6 +5,18 @@ namespace DotNetty.Common.Utilities
 {
  using System;
 
+ internal static class AttributeKey
+ {
+ // Keep the instance of AttributeConstantPool out of generic classes, to make it an really singleton for different generic types.
+ // see https://github.com/Azure/DotNetty/issues/498
+ public static readonly ConstantPool Pool = new AttributeConstantPool();
+
+ sealed class AttributeConstantPool : ConstantPool
+ {
+ protected override IConstant NewConstant<TValue>(int id, string name) => new AttributeKey<TValue>(id, name);
+ };
+ }
+
  /// <summary>
  /// Key which can be used to access <seealso cref="Attribute" /> out of the <see cref="IAttributeMap" />. Be aware that
  /// it is not be possible to have multiple keys with the same name.
@@ -14,12 +26,7 @@ namespace DotNetty.Common.Utilities
  /// </typeparam>
  public sealed class AttributeKey<T> : AbstractConstant<AttributeKey<T>>
  {
- public static readonly ConstantPool Pool = new AttributeConstantPool();
-
- sealed class AttributeConstantPool : ConstantPool
- {
- protected override IConstant NewConstant<TValue>(int id, string name) => new AttributeKey<TValue>(id, name);
- };
+ public static readonly ConstantPool Pool = AttributeKey.Pool;
 
  /// <summary>Returns the singleton instance of the {@link AttributeKey} which has the specified <c>name</c>.</summary>
  public static AttributeKey<T> ValueOf(string name) => (AttributeKey<T>)Pool.ValueOf<T>(name);