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CSHARP-5633: BsonSerializer.IsTypeDiscriminated is not thread-safe #1722

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CSHARP-5633: BsonSerializer.IsTypeDiscriminated is not thread-safe #1722

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CSHARP-5633: BsonSerializer.IsTypeDiscriminated is not thread-safe
papafe Jul 10, 2025
17d1324
Small fix
papafe Jul 14, 2025
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7 changes: 3 additions & 4 deletions src/MongoDB.Bson/Serialization/BsonSerializer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -39,7 +39,7 @@ public static class BsonSerializer
private static Dictionary<Type, IIdGenerator> __idGenerators = new Dictionary<Type, IIdGenerator>();
private static Dictionary<Type, IDiscriminatorConvention> __discriminatorConventions = new Dictionary<Type, IDiscriminatorConvention>();
private static Dictionary<BsonValue, HashSet<Type>> __discriminators = new Dictionary<BsonValue, HashSet<Type>>();
private static HashSet<Type> __discriminatedTypes = new HashSet<Type>();
private static ConcurrentDictionary<Type, bool> __discriminatedTypes = new ();
private static BsonSerializerRegistry __serializerRegistry;
private static TypeMappingSerializationProvider __typeMappingSerializationProvider;
// ConcurrentDictionary<Type, object> is being used as a concurrent set of Type. The values will always be null.
Expand Down Expand Up @@ -321,8 +321,7 @@ internal static bool IsDiscriminatorConventionRegisteredAtThisLevel(Type type)
/// <returns>True if the type is discriminated.</returns>
public static bool IsTypeDiscriminated(Type type)
{
var typeInfo = type.GetTypeInfo();
return typeInfo.IsInterface || __discriminatedTypes.Contains(type);
return type.GetTypeInfo().IsInterface || __discriminatedTypes.ContainsKey(type);
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GetTypeInfo is left over from when we used to target a very old .NET Core framework.

I think this line can be just:

return type.IsInterface || __discriminatedTypes.ContainsKey(type);

}

/// <summary>
Expand Down Expand Up @@ -587,7 +586,7 @@ public static void RegisterDiscriminator(Type type, BsonValue discriminator)
// mark all base types as discriminated (so we know that it's worth reading a discriminator)
for (var baseType = typeInfo.BaseType; baseType != null; baseType = baseType.GetTypeInfo().BaseType)
{
__discriminatedTypes.Add(baseType);
__discriminatedTypes.TryAdd(baseType, true);
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Is it OK that we are ignoring the return value of TryAdd?

I understand that we expect it to always return true given the check on line 582.

Should we document that we are ignoring the return value on purpose by coding like this:

_ = __discriminatedTypes.TryAdd(baseType, true);

}
}
}
Expand Down