Fix race condition when writing to __uniqueTypes

Author: mythz

src/ServiceStack.Text/JsConfig.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Reflection;
+using System.Threading;
 using ServiceStack.Text.Common;
 using ServiceStack.Text.Json;
 using ServiceStack.Text.Jsv;
@@ -624,7 +625,24 @@ internal static void InvokeReset(this Type genericType)
             methodInfo.Invoke(null, null);
         }
 
-        internal static HashSet<Type> __uniqueTypes = new HashSet<Type>(); 
+        internal static HashSet<Type> __uniqueTypes = new HashSet<Type>();
+        internal static int __uniqueTypesCount = 0;
+
+        internal static void AddUniqueType(Type type)
+        {
+            if (__uniqueTypes.Contains(type))
+                return;
+
+            HashSet<Type> newTypes, snapshot;
+            do
+            {
+                snapshot = __uniqueTypes;
+                newTypes = new HashSet<Type>(__uniqueTypes) { type };
+                __uniqueTypesCount = newTypes.Count;
+
+            } while (!ReferenceEquals(
+                Interlocked.CompareExchange(ref __uniqueTypes, newTypes, snapshot), snapshot));
+        }
     }
 
     public class JsConfig<T>

src/ServiceStack.Text/TypeConfig.cs

@@ -16,7 +16,7 @@ internal void AssertValidUsage()
         {
             if (!IsUserType) return;
 
-            LicenseUtils.AssertValidUsage(LicenseFeature.Text, QuotaType.Types, JsConfig.__uniqueTypes.Count);
+            LicenseUtils.AssertValidUsage(LicenseFeature.Text, QuotaType.Types, JsConfig.__uniqueTypesCount);
         }
 
         internal TypeConfig(Type type)
@@ -26,7 +26,7 @@ internal TypeConfig(Type type)
             Properties = new PropertyInfo[0];
             Fields = new FieldInfo[0];
 
-            JsConfig.__uniqueTypes.Add(Type);
+            JsConfig.AddUniqueType(Type);
         }
     }