Make TypeDescriptor thread safe with custom providers by enlarging lock region

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TypeDescriptor.cs

@@ -29,6 +29,7 @@ public sealed class TypeDescriptor
  private static readonly WeakHashtable s_providerTable = new WeakHashtable(); // mapping of type or object hash to a provider list
  private static readonly Hashtable s_providerTypeTable = new Hashtable(); // A direct mapping from type to provider.
  private static readonly Hashtable s_defaultProviders = new Hashtable(); // A table of type -> default provider to track DefaultTypeDescriptionProviderAttributes.
+ private static readonly Hashtable s_defaultProvidersChecked = new Hashtable(); // A table similar to s_defaultProviders but only set after providers are checked, in order to reduce locks.
  private static WeakHashtable? s_associationTable;
  private static int s_metadataVersion; // a version stamp for our metadata. Used by property descriptors to know when to rebuild attributes.
 
@@ -262,7 +263,9 @@ public static void AddProviderTransparent(TypeDescriptionProvider provider, obje
  /// </summary>
  private static void CheckDefaultProvider(Type type)
  {
- if (s_defaultProviders.ContainsKey(type))
+ bool providerAdded = false;
+
+ if (s_defaultProvidersChecked.ContainsKey(type))
  {
  return;
  }
@@ -278,26 +281,27 @@ private static void CheckDefaultProvider(Type type)
  // and it starts messing around with type information,
  // this could infinitely recurse.
  s_defaultProviders[type] = null;
- }
 
- // Always use core reflection when checking for
- // the default provider attribute. If there is a
- // provider, we probably don't want to build up our
- // own cache state against the type. There shouldn't be
- // more than one of these, but walk anyway. Walk in
- // reverse order so that the most derived takes precidence.
- object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
-bool providerAdded = false;
-for (int idx = attrs.Length - 1; idx >= 0; idx--)
-{
-TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
-Type? providerType = Type.GetType(pa.TypeName);
-if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
-{
-TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
-AddProvider(prov, type);
-providerAdded = true;
+// Always use core reflection when checking for
+// the default provider attribute. If there is a
+// provider, we probably don't want to build up our
+// own cache state against the type. There shouldn't be
+// more than one of these, but walk anyway. Walk in
+// reverse order so that the most derived takes precedence.
+object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
+ for (int idx = attrs.Length - 1; idx >= 0; idx--)
+ {
+ TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
+ Type? providerType = Type.GetType(pa.TypeName);
+ if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
+ {
+ TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
+ AddProvider(prov, type);
+ providerAdded = true;
+}
  }
+
+ s_defaultProvidersChecked[type] = null;
  }
 
  // If we did not add a provider, check the base class.

src/libraries/System.ComponentModel.TypeConverter/tests/TypeDescriptorTests.cs

@@ -5,6 +5,9 @@
 using System.Collections.Generic;
 using System.ComponentModel.Design;
 using System.Globalization;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 using Moq;
 using Xunit;
 
@@ -1231,5 +1234,196 @@ protected DerivedCultureInfo() : base("hello")
  class TwiceDerivedCultureInfo : DerivedCultureInfo
  {
  }
+
+ private long _concurrentError = 0;
+ private bool ConcurrentError
+ {
+ get => Interlocked.Read(ref _concurrentError) == 1;
+ set => Interlocked.Exchange(ref _concurrentError, value ? 1 : 0);
+ }
+
+ private void ConcurrentTest(TypeWithProperty instance)
+ {
+ var properties = TypeDescriptor.GetProperties(instance);
+ Thread.Sleep(10);
+ if (properties.Count > 0)
+ {
+ ConcurrentError = true;
+ }
+ }
+
+ [SkipOnPlatform(TestPlatforms.Browser, "Thread.Start is not supported on browsers.")]
+ [Fact]
+ public void ConcurrentGetProperties_ReturnsExpected()
+ {
+ const int Timeout = 60000;
+ int concurrentCount = Environment.ProcessorCount * 2;
+
+ using var finished = new CountdownEvent(concurrentCount);
+
+ var instances = new TypeWithProperty[concurrentCount];
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ instances[i] = new TypeWithProperty();
+ }
+
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ int i2 = i;
+ new Thread(() =>
+ {
+ ConcurrentTest(instances[i2]);
+ finished.Signal();
+ }).Start();
+ }
+
+ finished.Wait(Timeout);
+
+ if (finished.CurrentCount != 0)
+ {
+ Assert.Fail("Timeout. Possible deadlock.");
+ }
+ else
+ {
+ Assert.False(ConcurrentError, "Fallback type descriptor is used. Possible race condition.");
+ }
+ }
+
+ public sealed class EmptyPropertiesTypeProvider : TypeDescriptionProvider
+ {
+ private sealed class EmptyPropertyListDescriptor : ICustomTypeDescriptor
+ {
+ public AttributeCollection GetAttributes() => AttributeCollection.Empty;
+
+ public string? GetClassName() => null;
+
+ public string? GetComponentName() => null;
+
+ public TypeConverter? GetConverter() => new TypeConverter();
+
+ public EventDescriptor? GetDefaultEvent() => null;
+
+ public PropertyDescriptor? GetDefaultProperty() => null;
+
+ public object? GetEditor(Type editorBaseType) => null;
+
+ public EventDescriptorCollection GetEvents() => EventDescriptorCollection.Empty;
+
+ public EventDescriptorCollection GetEvents(Attribute[]? attributes) => GetEvents();
+
+ public PropertyDescriptorCollection GetProperties() => PropertyDescriptorCollection.Empty;
+
+ public PropertyDescriptorCollection GetProperties(Attribute[]? attributes) => GetProperties();
+
+ public object? GetPropertyOwner(PropertyDescriptor? pd) => null;
+ }
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object? instance)
+ {
+ return new EmptyPropertyListDescriptor();
+ }
+ }
+
+ [TypeDescriptionProvider(typeof(EmptyPropertiesTypeProvider))]
+ public sealed class TypeWithProperty
+ {
+ public int OneProperty { get; set; }
+ }
+
+ public static IEnumerable<object[]> GetConverter_ByMultithread_ReturnsExpected_TestData()
+ {
+ yield return new object[] { typeof(MyClass), typeof(MyTypeConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithCustomTypeDescriptionProvider), typeof(MyInheritedClassWithCustomTypeDescriptionProviderConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithInheritedTypeDescriptionProvider), typeof(MyTypeConverter) };
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverter_ByMultithread_ReturnsExpected_TestData))]
+ public async void GetConverter_ByMultithread_ReturnsExpected(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 100).Select(_ =>
+ Task.Run(() => TypeDescriptor.GetConverter(typeForGetConverter))));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ public static IEnumerable<object[]> GetConverterWithAddProvider_ByMultithread_Success_TestData()
+ {
+ foreach (object[] currentTestCase in GetConverter_ByMultithread_ReturnsExpected_TestData())
+ {
+ yield return currentTestCase;
+ }
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverterWithAddProvider_ByMultithread_Success_TestData))]
+ public async void GetConverterWithAddProvider_ByMultithread_Success(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 200).Select(_ =>
+ Task.Run(() =>
+ {
+ var mockProvider = new Mock<TypeDescriptionProvider>(MockBehavior.Strict);
+ var someInstance = new object();
+ TypeDescriptor.AddProvider(mockProvider.Object, someInstance);
+ return TypeDescriptor.GetConverter(typeForGetConverter);
+ })));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ [TypeDescriptionProvider(typeof(MyClassTypeDescriptionProvider))]
+ public class MyClass
+ {
+ }
+
+ [TypeDescriptionProvider(typeof(MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider))]
+ public class MyInheritedClassWithCustomTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyInheritedClassWithInheritedTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyClassTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyClassTypeDescriptor();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor();
+ }
+ }
+
+ public class MyClassTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyTypeConverter();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderConverter();
+ }
+ }
+
+ public class MyTypeConverter : TypeConverter
+ {
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderConverter : TypeConverter
+ {
+ }
  }
 }

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TypeDescriptor.cs

@@ -29,6 +29,7 @@ public sealed class TypeDescriptor
  private static readonly WeakHashtable s_providerTable = new WeakHashtable(); // mapping of type or object hash to a provider list
  private static readonly Hashtable s_providerTypeTable = new Hashtable(); // A direct mapping from type to provider.
  private static readonly Hashtable s_defaultProviders = new Hashtable(); // A table of type -> default provider to track DefaultTypeDescriptionProviderAttributes.
+ private static readonly Hashtable s_defaultProvidersChecked = new Hashtable(); // A table similar to s_defaultProviders but only set after providers are checked, in order to reduce locks.
  private static WeakHashtable? s_associationTable;
  private static int s_metadataVersion; // a version stamp for our metadata. Used by property descriptors to know when to rebuild attributes.
 
@@ -262,7 +263,9 @@ public static void AddProviderTransparent(TypeDescriptionProvider provider, obje
  /// </summary>
  private static void CheckDefaultProvider(Type type)
  {
- if (s_defaultProviders.ContainsKey(type))
+ bool providerAdded = false;
+
+ if (s_defaultProvidersChecked.ContainsKey(type))
  {
  return;
  }
@@ -278,26 +281,27 @@ private static void CheckDefaultProvider(Type type)
  // and it starts messing around with type information,
  // this could infinitely recurse.
  s_defaultProviders[type] = null;
- }
 
- // Always use core reflection when checking for
- // the default provider attribute. If there is a
- // provider, we probably don't want to build up our
- // own cache state against the type. There shouldn't be
- // more than one of these, but walk anyway. Walk in
- // reverse order so that the most derived takes precidence.
- object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
-bool providerAdded = false;
-for (int idx = attrs.Length - 1; idx >= 0; idx--)
-{
-TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
-Type? providerType = Type.GetType(pa.TypeName);
-if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
-{
-TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
-AddProvider(prov, type);
-providerAdded = true;
+// Always use core reflection when checking for
+// the default provider attribute. If there is a
+// provider, we probably don't want to build up our
+// own cache state against the type. There shouldn't be
+// more than one of these, but walk anyway. Walk in
+// reverse order so that the most derived takes precedence.
+object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
+ for (int idx = attrs.Length - 1; idx >= 0; idx--)
+ {
+ TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
+ Type? providerType = Type.GetType(pa.TypeName);
+ if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
+ {
+ TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
+ AddProvider(prov, type);
+ providerAdded = true;
+}
  }
+
+ s_defaultProvidersChecked[type] = null;
  }
 
  // If we did not add a provider, check the base class.

src/libraries/System.ComponentModel.TypeConverter/tests/TypeDescriptorTests.cs

@@ -5,6 +5,9 @@
 using System.Collections.Generic;
 using System.ComponentModel.Design;
 using System.Globalization;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 using Moq;
 using Xunit;
 
@@ -1231,5 +1234,196 @@ protected DerivedCultureInfo() : base("hello")
  class TwiceDerivedCultureInfo : DerivedCultureInfo
  {
  }
+
+ private long _concurrentError = 0;
+ private bool ConcurrentError
+ {
+ get => Interlocked.Read(ref _concurrentError) == 1;
+ set => Interlocked.Exchange(ref _concurrentError, value ? 1 : 0);
+ }
+
+ private void ConcurrentTest(TypeWithProperty instance)
+ {
+ var properties = TypeDescriptor.GetProperties(instance);
+ Thread.Sleep(10);
+ if (properties.Count > 0)
+ {
+ ConcurrentError = true;
+ }
+ }
+
+ [SkipOnPlatform(TestPlatforms.Browser, "Thread.Start is not supported on browsers.")]
+ [Fact]
+ public void ConcurrentGetProperties_ReturnsExpected()
+ {
+ const int Timeout = 60000;
+ int concurrentCount = Environment.ProcessorCount * 2;
+
+ using var finished = new CountdownEvent(concurrentCount);
+
+ var instances = new TypeWithProperty[concurrentCount];
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ instances[i] = new TypeWithProperty();
+ }
+
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ int i2 = i;
+ new Thread(() =>
+ {
+ ConcurrentTest(instances[i2]);
+ finished.Signal();
+ }).Start();
+ }
+
+ finished.Wait(Timeout);
+
+ if (finished.CurrentCount != 0)
+ {
+ Assert.Fail("Timeout. Possible deadlock.");
+ }
+ else
+ {
+ Assert.False(ConcurrentError, "Fallback type descriptor is used. Possible race condition.");
+ }
+ }
+
+ public sealed class EmptyPropertiesTypeProvider : TypeDescriptionProvider
+ {
+ private sealed class EmptyPropertyListDescriptor : ICustomTypeDescriptor
+ {
+ public AttributeCollection GetAttributes() => AttributeCollection.Empty;
+
+ public string? GetClassName() => null;
+
+ public string? GetComponentName() => null;
+
+ public TypeConverter? GetConverter() => new TypeConverter();
+
+ public EventDescriptor? GetDefaultEvent() => null;
+
+ public PropertyDescriptor? GetDefaultProperty() => null;
+
+ public object? GetEditor(Type editorBaseType) => null;
+
+ public EventDescriptorCollection GetEvents() => EventDescriptorCollection.Empty;
+
+ public EventDescriptorCollection GetEvents(Attribute[]? attributes) => GetEvents();
+
+ public PropertyDescriptorCollection GetProperties() => PropertyDescriptorCollection.Empty;
+
+ public PropertyDescriptorCollection GetProperties(Attribute[]? attributes) => GetProperties();
+
+ public object? GetPropertyOwner(PropertyDescriptor? pd) => null;
+ }
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object? instance)
+ {
+ return new EmptyPropertyListDescriptor();
+ }
+ }
+
+ [TypeDescriptionProvider(typeof(EmptyPropertiesTypeProvider))]
+ public sealed class TypeWithProperty
+ {
+ public int OneProperty { get; set; }
+ }
+
+ public static IEnumerable<object[]> GetConverter_ByMultithread_ReturnsExpected_TestData()
+ {
+ yield return new object[] { typeof(MyClass), typeof(MyTypeConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithCustomTypeDescriptionProvider), typeof(MyInheritedClassWithCustomTypeDescriptionProviderConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithInheritedTypeDescriptionProvider), typeof(MyTypeConverter) };
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverter_ByMultithread_ReturnsExpected_TestData))]
+ public async void GetConverter_ByMultithread_ReturnsExpected(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 100).Select(_ =>
+ Task.Run(() => TypeDescriptor.GetConverter(typeForGetConverter))));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ public static IEnumerable<object[]> GetConverterWithAddProvider_ByMultithread_Success_TestData()
+ {
+ foreach (object[] currentTestCase in GetConverter_ByMultithread_ReturnsExpected_TestData())
+ {
+ yield return currentTestCase;
+ }
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverterWithAddProvider_ByMultithread_Success_TestData))]
+ public async void GetConverterWithAddProvider_ByMultithread_Success(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 200).Select(_ =>
+ Task.Run(() =>
+ {
+ var mockProvider = new Mock<TypeDescriptionProvider>(MockBehavior.Strict);
+ var someInstance = new object();
+ TypeDescriptor.AddProvider(mockProvider.Object, someInstance);
+ return TypeDescriptor.GetConverter(typeForGetConverter);
+ })));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ [TypeDescriptionProvider(typeof(MyClassTypeDescriptionProvider))]
+ public class MyClass
+ {
+ }
+
+ [TypeDescriptionProvider(typeof(MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider))]
+ public class MyInheritedClassWithCustomTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyInheritedClassWithInheritedTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyClassTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyClassTypeDescriptor();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor();
+ }
+ }
+
+ public class MyClassTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyTypeConverter();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderConverter();
+ }
+ }
+
+ public class MyTypeConverter : TypeConverter
+ {
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderConverter : TypeConverter
+ {
+ }
  }
 }

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TypeDescriptor.cs

@@ -29,6 +29,7 @@ public sealed class TypeDescriptor
  private static readonly WeakHashtable s_providerTable = new WeakHashtable(); // mapping of type or object hash to a provider list
  private static readonly Hashtable s_providerTypeTable = new Hashtable(); // A direct mapping from type to provider.
  private static readonly Hashtable s_defaultProviders = new Hashtable(); // A table of type -> default provider to track DefaultTypeDescriptionProviderAttributes.
+ private static readonly Hashtable s_defaultProvidersChecked = new Hashtable(); // A table similar to s_defaultProviders but only set after providers are checked, in order to reduce locks.
  private static WeakHashtable? s_associationTable;
  private static int s_metadataVersion; // a version stamp for our metadata. Used by property descriptors to know when to rebuild attributes.
 
@@ -262,7 +263,9 @@ public static void AddProviderTransparent(TypeDescriptionProvider provider, obje
  /// </summary>
  private static void CheckDefaultProvider(Type type)
  {
- if (s_defaultProviders.ContainsKey(type))
+ bool providerAdded = false;
+
+ if (s_defaultProvidersChecked.ContainsKey(type))
  {
  return;
  }
@@ -278,26 +281,27 @@ private static void CheckDefaultProvider(Type type)
  // and it starts messing around with type information,
  // this could infinitely recurse.
  s_defaultProviders[type] = null;
- }
 
- // Always use core reflection when checking for
- // the default provider attribute. If there is a
- // provider, we probably don't want to build up our
- // own cache state against the type. There shouldn't be
- // more than one of these, but walk anyway. Walk in
- // reverse order so that the most derived takes precidence.
- object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
-bool providerAdded = false;
-for (int idx = attrs.Length - 1; idx >= 0; idx--)
-{
-TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
-Type? providerType = Type.GetType(pa.TypeName);
-if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
-{
-TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
-AddProvider(prov, type);
-providerAdded = true;
+// Always use core reflection when checking for
+// the default provider attribute. If there is a
+// provider, we probably don't want to build up our
+// own cache state against the type. There shouldn't be
+// more than one of these, but walk anyway. Walk in
+// reverse order so that the most derived takes precedence.
+object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
+ for (int idx = attrs.Length - 1; idx >= 0; idx--)
+ {
+ TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
+ Type? providerType = Type.GetType(pa.TypeName);
+ if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
+ {
+ TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
+ AddProvider(prov, type);
+ providerAdded = true;
+}
  }
+
+ s_defaultProvidersChecked[type] = null;
  }
 
  // If we did not add a provider, check the base class.

src/libraries/System.ComponentModel.TypeConverter/tests/TypeDescriptorTests.cs

@@ -5,6 +5,9 @@
 using System.Collections.Generic;
 using System.ComponentModel.Design;
 using System.Globalization;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 using Moq;
 using Xunit;
 
@@ -1231,5 +1234,196 @@ protected DerivedCultureInfo() : base("hello")
  class TwiceDerivedCultureInfo : DerivedCultureInfo
  {
  }
+
+ private long _concurrentError = 0;
+ private bool ConcurrentError
+ {
+ get => Interlocked.Read(ref _concurrentError) == 1;
+ set => Interlocked.Exchange(ref _concurrentError, value ? 1 : 0);
+ }
+
+ private void ConcurrentTest(TypeWithProperty instance)
+ {
+ var properties = TypeDescriptor.GetProperties(instance);
+ Thread.Sleep(10);
+ if (properties.Count > 0)
+ {
+ ConcurrentError = true;
+ }
+ }
+
+ [SkipOnPlatform(TestPlatforms.Browser, "Thread.Start is not supported on browsers.")]
+ [Fact]
+ public void ConcurrentGetProperties_ReturnsExpected()
+ {
+ const int Timeout = 60000;
+ int concurrentCount = Environment.ProcessorCount * 2;
+
+ using var finished = new CountdownEvent(concurrentCount);
+
+ var instances = new TypeWithProperty[concurrentCount];
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ instances[i] = new TypeWithProperty();
+ }
+
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ int i2 = i;
+ new Thread(() =>
+ {
+ ConcurrentTest(instances[i2]);
+ finished.Signal();
+ }).Start();
+ }
+
+ finished.Wait(Timeout);
+
+ if (finished.CurrentCount != 0)
+ {
+ Assert.Fail("Timeout. Possible deadlock.");
+ }
+ else
+ {
+ Assert.False(ConcurrentError, "Fallback type descriptor is used. Possible race condition.");
+ }
+ }
+
+ public sealed class EmptyPropertiesTypeProvider : TypeDescriptionProvider
+ {
+ private sealed class EmptyPropertyListDescriptor : ICustomTypeDescriptor
+ {
+ public AttributeCollection GetAttributes() => AttributeCollection.Empty;
+
+ public string? GetClassName() => null;
+
+ public string? GetComponentName() => null;
+
+ public TypeConverter? GetConverter() => new TypeConverter();
+
+ public EventDescriptor? GetDefaultEvent() => null;
+
+ public PropertyDescriptor? GetDefaultProperty() => null;
+
+ public object? GetEditor(Type editorBaseType) => null;
+
+ public EventDescriptorCollection GetEvents() => EventDescriptorCollection.Empty;
+
+ public EventDescriptorCollection GetEvents(Attribute[]? attributes) => GetEvents();
+
+ public PropertyDescriptorCollection GetProperties() => PropertyDescriptorCollection.Empty;
+
+ public PropertyDescriptorCollection GetProperties(Attribute[]? attributes) => GetProperties();
+
+ public object? GetPropertyOwner(PropertyDescriptor? pd) => null;
+ }
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object? instance)
+ {
+ return new EmptyPropertyListDescriptor();
+ }
+ }
+
+ [TypeDescriptionProvider(typeof(EmptyPropertiesTypeProvider))]
+ public sealed class TypeWithProperty
+ {
+ public int OneProperty { get; set; }
+ }
+
+ public static IEnumerable<object[]> GetConverter_ByMultithread_ReturnsExpected_TestData()
+ {
+ yield return new object[] { typeof(MyClass), typeof(MyTypeConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithCustomTypeDescriptionProvider), typeof(MyInheritedClassWithCustomTypeDescriptionProviderConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithInheritedTypeDescriptionProvider), typeof(MyTypeConverter) };
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverter_ByMultithread_ReturnsExpected_TestData))]
+ public async void GetConverter_ByMultithread_ReturnsExpected(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 100).Select(_ =>
+ Task.Run(() => TypeDescriptor.GetConverter(typeForGetConverter))));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ public static IEnumerable<object[]> GetConverterWithAddProvider_ByMultithread_Success_TestData()
+ {
+ foreach (object[] currentTestCase in GetConverter_ByMultithread_ReturnsExpected_TestData())
+ {
+ yield return currentTestCase;
+ }
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverterWithAddProvider_ByMultithread_Success_TestData))]
+ public async void GetConverterWithAddProvider_ByMultithread_Success(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 200).Select(_ =>
+ Task.Run(() =>
+ {
+ var mockProvider = new Mock<TypeDescriptionProvider>(MockBehavior.Strict);
+ var someInstance = new object();
+ TypeDescriptor.AddProvider(mockProvider.Object, someInstance);
+ return TypeDescriptor.GetConverter(typeForGetConverter);
+ })));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ [TypeDescriptionProvider(typeof(MyClassTypeDescriptionProvider))]
+ public class MyClass
+ {
+ }
+
+ [TypeDescriptionProvider(typeof(MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider))]
+ public class MyInheritedClassWithCustomTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyInheritedClassWithInheritedTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyClassTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyClassTypeDescriptor();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor();
+ }
+ }
+
+ public class MyClassTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyTypeConverter();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderConverter();
+ }
+ }
+
+ public class MyTypeConverter : TypeConverter
+ {
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderConverter : TypeConverter
+ {
+ }
  }
 }

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TypeDescriptor.cs

@@ -29,6 +29,7 @@ public sealed class TypeDescriptor
  private static readonly WeakHashtable s_providerTable = new WeakHashtable(); // mapping of type or object hash to a provider list
  private static readonly Hashtable s_providerTypeTable = new Hashtable(); // A direct mapping from type to provider.
  private static readonly Hashtable s_defaultProviders = new Hashtable(); // A table of type -> default provider to track DefaultTypeDescriptionProviderAttributes.
+ private static readonly Hashtable s_defaultProvidersChecked = new Hashtable(); // A table similar to s_defaultProviders but only set after providers are checked, in order to reduce locks.
  private static WeakHashtable? s_associationTable;
  private static int s_metadataVersion; // a version stamp for our metadata. Used by property descriptors to know when to rebuild attributes.
 
@@ -262,7 +263,9 @@ public static void AddProviderTransparent(TypeDescriptionProvider provider, obje
  /// </summary>
  private static void CheckDefaultProvider(Type type)
  {
- if (s_defaultProviders.ContainsKey(type))
+ bool providerAdded = false;
+
+ if (s_defaultProvidersChecked.ContainsKey(type))
  {
  return;
  }
@@ -278,26 +281,27 @@ private static void CheckDefaultProvider(Type type)
  // and it starts messing around with type information,
  // this could infinitely recurse.
  s_defaultProviders[type] = null;
- }
 
- // Always use core reflection when checking for
- // the default provider attribute. If there is a
- // provider, we probably don't want to build up our
- // own cache state against the type. There shouldn't be
- // more than one of these, but walk anyway. Walk in
- // reverse order so that the most derived takes precidence.
- object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
-bool providerAdded = false;
-for (int idx = attrs.Length - 1; idx >= 0; idx--)
-{
-TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
-Type? providerType = Type.GetType(pa.TypeName);
-if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
-{
-TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
-AddProvider(prov, type);
-providerAdded = true;
+// Always use core reflection when checking for
+// the default provider attribute. If there is a
+// provider, we probably don't want to build up our
+// own cache state against the type. There shouldn't be
+// more than one of these, but walk anyway. Walk in
+// reverse order so that the most derived takes precedence.
+object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
+ for (int idx = attrs.Length - 1; idx >= 0; idx--)
+ {
+ TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
+ Type? providerType = Type.GetType(pa.TypeName);
+ if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
+ {
+ TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
+ AddProvider(prov, type);
+ providerAdded = true;
+}
  }
+
+ s_defaultProvidersChecked[type] = null;
  }
 
  // If we did not add a provider, check the base class.

src/libraries/System.ComponentModel.TypeConverter/tests/TypeDescriptorTests.cs

@@ -5,6 +5,9 @@
 using System.Collections.Generic;
 using System.ComponentModel.Design;
 using System.Globalization;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 using Moq;
 using Xunit;
 
@@ -1231,5 +1234,196 @@ protected DerivedCultureInfo() : base("hello")
  class TwiceDerivedCultureInfo : DerivedCultureInfo
  {
  }
+
+ private long _concurrentError = 0;
+ private bool ConcurrentError
+ {
+ get => Interlocked.Read(ref _concurrentError) == 1;
+ set => Interlocked.Exchange(ref _concurrentError, value ? 1 : 0);
+ }
+
+ private void ConcurrentTest(TypeWithProperty instance)
+ {
+ var properties = TypeDescriptor.GetProperties(instance);
+ Thread.Sleep(10);
+ if (properties.Count > 0)
+ {
+ ConcurrentError = true;
+ }
+ }
+
+ [SkipOnPlatform(TestPlatforms.Browser, "Thread.Start is not supported on browsers.")]
+ [Fact]
+ public void ConcurrentGetProperties_ReturnsExpected()
+ {
+ const int Timeout = 60000;
+ int concurrentCount = Environment.ProcessorCount * 2;
+
+ using var finished = new CountdownEvent(concurrentCount);
+
+ var instances = new TypeWithProperty[concurrentCount];
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ instances[i] = new TypeWithProperty();
+ }
+
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ int i2 = i;
+ new Thread(() =>
+ {
+ ConcurrentTest(instances[i2]);
+ finished.Signal();
+ }).Start();
+ }
+
+ finished.Wait(Timeout);
+
+ if (finished.CurrentCount != 0)
+ {
+ Assert.Fail("Timeout. Possible deadlock.");
+ }
+ else
+ {
+ Assert.False(ConcurrentError, "Fallback type descriptor is used. Possible race condition.");
+ }
+ }
+
+ public sealed class EmptyPropertiesTypeProvider : TypeDescriptionProvider
+ {
+ private sealed class EmptyPropertyListDescriptor : ICustomTypeDescriptor
+ {
+ public AttributeCollection GetAttributes() => AttributeCollection.Empty;
+
+ public string? GetClassName() => null;
+
+ public string? GetComponentName() => null;
+
+ public TypeConverter? GetConverter() => new TypeConverter();
+
+ public EventDescriptor? GetDefaultEvent() => null;
+
+ public PropertyDescriptor? GetDefaultProperty() => null;
+
+ public object? GetEditor(Type editorBaseType) => null;
+
+ public EventDescriptorCollection GetEvents() => EventDescriptorCollection.Empty;
+
+ public EventDescriptorCollection GetEvents(Attribute[]? attributes) => GetEvents();
+
+ public PropertyDescriptorCollection GetProperties() => PropertyDescriptorCollection.Empty;
+
+ public PropertyDescriptorCollection GetProperties(Attribute[]? attributes) => GetProperties();
+
+ public object? GetPropertyOwner(PropertyDescriptor? pd) => null;
+ }
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object? instance)
+ {
+ return new EmptyPropertyListDescriptor();
+ }
+ }
+
+ [TypeDescriptionProvider(typeof(EmptyPropertiesTypeProvider))]
+ public sealed class TypeWithProperty
+ {
+ public int OneProperty { get; set; }
+ }
+
+ public static IEnumerable<object[]> GetConverter_ByMultithread_ReturnsExpected_TestData()
+ {
+ yield return new object[] { typeof(MyClass), typeof(MyTypeConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithCustomTypeDescriptionProvider), typeof(MyInheritedClassWithCustomTypeDescriptionProviderConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithInheritedTypeDescriptionProvider), typeof(MyTypeConverter) };
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverter_ByMultithread_ReturnsExpected_TestData))]
+ public async void GetConverter_ByMultithread_ReturnsExpected(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 100).Select(_ =>
+ Task.Run(() => TypeDescriptor.GetConverter(typeForGetConverter))));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ public static IEnumerable<object[]> GetConverterWithAddProvider_ByMultithread_Success_TestData()
+ {
+ foreach (object[] currentTestCase in GetConverter_ByMultithread_ReturnsExpected_TestData())
+ {
+ yield return currentTestCase;
+ }
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverterWithAddProvider_ByMultithread_Success_TestData))]
+ public async void GetConverterWithAddProvider_ByMultithread_Success(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 200).Select(_ =>
+ Task.Run(() =>
+ {
+ var mockProvider = new Mock<TypeDescriptionProvider>(MockBehavior.Strict);
+ var someInstance = new object();
+ TypeDescriptor.AddProvider(mockProvider.Object, someInstance);
+ return TypeDescriptor.GetConverter(typeForGetConverter);
+ })));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ [TypeDescriptionProvider(typeof(MyClassTypeDescriptionProvider))]
+ public class MyClass
+ {
+ }
+
+ [TypeDescriptionProvider(typeof(MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider))]
+ public class MyInheritedClassWithCustomTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyInheritedClassWithInheritedTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyClassTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyClassTypeDescriptor();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor();
+ }
+ }
+
+ public class MyClassTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyTypeConverter();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderConverter();
+ }
+ }
+
+ public class MyTypeConverter : TypeConverter
+ {
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderConverter : TypeConverter
+ {
+ }
  }
 }

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TypeDescriptor.cs

@@ -29,6 +29,7 @@ public sealed class TypeDescriptor
  private static readonly WeakHashtable s_providerTable = new WeakHashtable(); // mapping of type or object hash to a provider list
  private static readonly Hashtable s_providerTypeTable = new Hashtable(); // A direct mapping from type to provider.
  private static readonly Hashtable s_defaultProviders = new Hashtable(); // A table of type -> default provider to track DefaultTypeDescriptionProviderAttributes.
+ private static readonly Hashtable s_defaultProvidersChecked = new Hashtable(); // A table similar to s_defaultProviders but only set after providers are checked, in order to reduce locks.
  private static WeakHashtable? s_associationTable;
  private static int s_metadataVersion; // a version stamp for our metadata. Used by property descriptors to know when to rebuild attributes.
 
@@ -262,7 +263,9 @@ public static void AddProviderTransparent(TypeDescriptionProvider provider, obje
  /// </summary>
  private static void CheckDefaultProvider(Type type)
  {
- if (s_defaultProviders.ContainsKey(type))
+ bool providerAdded = false;
+
+ if (s_defaultProvidersChecked.ContainsKey(type))
  {
  return;
  }
@@ -278,26 +281,27 @@ private static void CheckDefaultProvider(Type type)
  // and it starts messing around with type information,
  // this could infinitely recurse.
  s_defaultProviders[type] = null;
- }
 
- // Always use core reflection when checking for
- // the default provider attribute. If there is a
- // provider, we probably don't want to build up our
- // own cache state against the type. There shouldn't be
- // more than one of these, but walk anyway. Walk in
- // reverse order so that the most derived takes precidence.
- object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
-bool providerAdded = false;
-for (int idx = attrs.Length - 1; idx >= 0; idx--)
-{
-TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
-Type? providerType = Type.GetType(pa.TypeName);
-if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
-{
-TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
-AddProvider(prov, type);
-providerAdded = true;
+// Always use core reflection when checking for
+// the default provider attribute. If there is a
+// provider, we probably don't want to build up our
+// own cache state against the type. There shouldn't be
+// more than one of these, but walk anyway. Walk in
+// reverse order so that the most derived takes precedence.
+object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
+ for (int idx = attrs.Length - 1; idx >= 0; idx--)
+ {
+ TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
+ Type? providerType = Type.GetType(pa.TypeName);
+ if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
+ {
+ TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
+ AddProvider(prov, type);
+ providerAdded = true;
+}
  }
+
+ s_defaultProvidersChecked[type] = null;
  }
 
  // If we did not add a provider, check the base class.

src/libraries/System.ComponentModel.TypeConverter/tests/TypeDescriptorTests.cs

@@ -5,6 +5,9 @@
 using System.Collections.Generic;
 using System.ComponentModel.Design;
 using System.Globalization;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 using Moq;
 using Xunit;
 
@@ -1231,5 +1234,196 @@ protected DerivedCultureInfo() : base("hello")
  class TwiceDerivedCultureInfo : DerivedCultureInfo
  {
  }
+
+ private long _concurrentError = 0;
+ private bool ConcurrentError
+ {
+ get => Interlocked.Read(ref _concurrentError) == 1;
+ set => Interlocked.Exchange(ref _concurrentError, value ? 1 : 0);
+ }
+
+ private void ConcurrentTest(TypeWithProperty instance)
+ {
+ var properties = TypeDescriptor.GetProperties(instance);
+ Thread.Sleep(10);
+ if (properties.Count > 0)
+ {
+ ConcurrentError = true;
+ }
+ }
+
+ [SkipOnPlatform(TestPlatforms.Browser, "Thread.Start is not supported on browsers.")]
+ [Fact]
+ public void ConcurrentGetProperties_ReturnsExpected()
+ {
+ const int Timeout = 60000;
+ int concurrentCount = Environment.ProcessorCount * 2;
+
+ using var finished = new CountdownEvent(concurrentCount);
+
+ var instances = new TypeWithProperty[concurrentCount];
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ instances[i] = new TypeWithProperty();
+ }
+
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ int i2 = i;
+ new Thread(() =>
+ {
+ ConcurrentTest(instances[i2]);
+ finished.Signal();
+ }).Start();
+ }
+
+ finished.Wait(Timeout);
+
+ if (finished.CurrentCount != 0)
+ {
+ Assert.Fail("Timeout. Possible deadlock.");
+ }
+ else
+ {
+ Assert.False(ConcurrentError, "Fallback type descriptor is used. Possible race condition.");
+ }
+ }
+
+ public sealed class EmptyPropertiesTypeProvider : TypeDescriptionProvider
+ {
+ private sealed class EmptyPropertyListDescriptor : ICustomTypeDescriptor
+ {
+ public AttributeCollection GetAttributes() => AttributeCollection.Empty;
+
+ public string? GetClassName() => null;
+
+ public string? GetComponentName() => null;
+
+ public TypeConverter? GetConverter() => new TypeConverter();
+
+ public EventDescriptor? GetDefaultEvent() => null;
+
+ public PropertyDescriptor? GetDefaultProperty() => null;
+
+ public object? GetEditor(Type editorBaseType) => null;
+
+ public EventDescriptorCollection GetEvents() => EventDescriptorCollection.Empty;
+
+ public EventDescriptorCollection GetEvents(Attribute[]? attributes) => GetEvents();
+
+ public PropertyDescriptorCollection GetProperties() => PropertyDescriptorCollection.Empty;
+
+ public PropertyDescriptorCollection GetProperties(Attribute[]? attributes) => GetProperties();
+
+ public object? GetPropertyOwner(PropertyDescriptor? pd) => null;
+ }
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object? instance)
+ {
+ return new EmptyPropertyListDescriptor();
+ }
+ }
+
+ [TypeDescriptionProvider(typeof(EmptyPropertiesTypeProvider))]
+ public sealed class TypeWithProperty
+ {
+ public int OneProperty { get; set; }
+ }
+
+ public static IEnumerable<object[]> GetConverter_ByMultithread_ReturnsExpected_TestData()
+ {
+ yield return new object[] { typeof(MyClass), typeof(MyTypeConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithCustomTypeDescriptionProvider), typeof(MyInheritedClassWithCustomTypeDescriptionProviderConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithInheritedTypeDescriptionProvider), typeof(MyTypeConverter) };
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverter_ByMultithread_ReturnsExpected_TestData))]
+ public async void GetConverter_ByMultithread_ReturnsExpected(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 100).Select(_ =>
+ Task.Run(() => TypeDescriptor.GetConverter(typeForGetConverter))));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ public static IEnumerable<object[]> GetConverterWithAddProvider_ByMultithread_Success_TestData()
+ {
+ foreach (object[] currentTestCase in GetConverter_ByMultithread_ReturnsExpected_TestData())
+ {
+ yield return currentTestCase;
+ }
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverterWithAddProvider_ByMultithread_Success_TestData))]
+ public async void GetConverterWithAddProvider_ByMultithread_Success(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 200).Select(_ =>
+ Task.Run(() =>
+ {
+ var mockProvider = new Mock<TypeDescriptionProvider>(MockBehavior.Strict);
+ var someInstance = new object();
+ TypeDescriptor.AddProvider(mockProvider.Object, someInstance);
+ return TypeDescriptor.GetConverter(typeForGetConverter);
+ })));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ [TypeDescriptionProvider(typeof(MyClassTypeDescriptionProvider))]
+ public class MyClass
+ {
+ }
+
+ [TypeDescriptionProvider(typeof(MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider))]
+ public class MyInheritedClassWithCustomTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyInheritedClassWithInheritedTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyClassTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyClassTypeDescriptor();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor();
+ }
+ }
+
+ public class MyClassTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyTypeConverter();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderConverter();
+ }
+ }
+
+ public class MyTypeConverter : TypeConverter
+ {
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderConverter : TypeConverter
+ {
+ }
  }
 }

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TypeDescriptor.cs

@@ -29,6 +29,7 @@ public sealed class TypeDescriptor
  private static readonly WeakHashtable s_providerTable = new WeakHashtable(); // mapping of type or object hash to a provider list
  private static readonly Hashtable s_providerTypeTable = new Hashtable(); // A direct mapping from type to provider.
  private static readonly Hashtable s_defaultProviders = new Hashtable(); // A table of type -> default provider to track DefaultTypeDescriptionProviderAttributes.
+ private static readonly Hashtable s_defaultProvidersChecked = new Hashtable(); // A table similar to s_defaultProviders but only set after providers are checked, in order to reduce locks.
  private static WeakHashtable? s_associationTable;
  private static int s_metadataVersion; // a version stamp for our metadata. Used by property descriptors to know when to rebuild attributes.
 
@@ -262,7 +263,9 @@ public static void AddProviderTransparent(TypeDescriptionProvider provider, obje
  /// </summary>
  private static void CheckDefaultProvider(Type type)
  {
- if (s_defaultProviders.ContainsKey(type))
+ bool providerAdded = false;
+
+ if (s_defaultProvidersChecked.ContainsKey(type))
  {
  return;
  }
@@ -278,26 +281,27 @@ private static void CheckDefaultProvider(Type type)
  // and it starts messing around with type information,
  // this could infinitely recurse.
  s_defaultProviders[type] = null;
- }
 
- // Always use core reflection when checking for
- // the default provider attribute. If there is a
- // provider, we probably don't want to build up our
- // own cache state against the type. There shouldn't be
- // more than one of these, but walk anyway. Walk in
- // reverse order so that the most derived takes precidence.
- object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
-bool providerAdded = false;
-for (int idx = attrs.Length - 1; idx >= 0; idx--)
-{
-TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
-Type? providerType = Type.GetType(pa.TypeName);
-if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
-{
-TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
-AddProvider(prov, type);
-providerAdded = true;
+// Always use core reflection when checking for
+// the default provider attribute. If there is a
+// provider, we probably don't want to build up our
+// own cache state against the type. There shouldn't be
+// more than one of these, but walk anyway. Walk in
+// reverse order so that the most derived takes precedence.
+object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
+ for (int idx = attrs.Length - 1; idx >= 0; idx--)
+ {
+ TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
+ Type? providerType = Type.GetType(pa.TypeName);
+ if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
+ {
+ TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
+ AddProvider(prov, type);
+ providerAdded = true;
+}
  }
+
+ s_defaultProvidersChecked[type] = null;
  }
 
  // If we did not add a provider, check the base class.

src/libraries/System.ComponentModel.TypeConverter/tests/TypeDescriptorTests.cs

@@ -5,6 +5,9 @@
 using System.Collections.Generic;
 using System.ComponentModel.Design;
 using System.Globalization;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 using Moq;
 using Xunit;
 
@@ -1231,5 +1234,196 @@ protected DerivedCultureInfo() : base("hello")
  class TwiceDerivedCultureInfo : DerivedCultureInfo
  {
  }
+
+ private long _concurrentError = 0;
+ private bool ConcurrentError
+ {
+ get => Interlocked.Read(ref _concurrentError) == 1;
+ set => Interlocked.Exchange(ref _concurrentError, value ? 1 : 0);
+ }
+
+ private void ConcurrentTest(TypeWithProperty instance)
+ {
+ var properties = TypeDescriptor.GetProperties(instance);
+ Thread.Sleep(10);
+ if (properties.Count > 0)
+ {
+ ConcurrentError = true;
+ }
+ }
+
+ [SkipOnPlatform(TestPlatforms.Browser, "Thread.Start is not supported on browsers.")]
+ [Fact]
+ public void ConcurrentGetProperties_ReturnsExpected()
+ {
+ const int Timeout = 60000;
+ int concurrentCount = Environment.ProcessorCount * 2;
+
+ using var finished = new CountdownEvent(concurrentCount);
+
+ var instances = new TypeWithProperty[concurrentCount];
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ instances[i] = new TypeWithProperty();
+ }
+
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ int i2 = i;
+ new Thread(() =>
+ {
+ ConcurrentTest(instances[i2]);
+ finished.Signal();
+ }).Start();
+ }
+
+ finished.Wait(Timeout);
+
+ if (finished.CurrentCount != 0)
+ {
+ Assert.Fail("Timeout. Possible deadlock.");
+ }
+ else
+ {
+ Assert.False(ConcurrentError, "Fallback type descriptor is used. Possible race condition.");
+ }
+ }
+
+ public sealed class EmptyPropertiesTypeProvider : TypeDescriptionProvider
+ {
+ private sealed class EmptyPropertyListDescriptor : ICustomTypeDescriptor
+ {
+ public AttributeCollection GetAttributes() => AttributeCollection.Empty;
+
+ public string? GetClassName() => null;
+
+ public string? GetComponentName() => null;
+
+ public TypeConverter? GetConverter() => new TypeConverter();
+
+ public EventDescriptor? GetDefaultEvent() => null;
+
+ public PropertyDescriptor? GetDefaultProperty() => null;
+
+ public object? GetEditor(Type editorBaseType) => null;
+
+ public EventDescriptorCollection GetEvents() => EventDescriptorCollection.Empty;
+
+ public EventDescriptorCollection GetEvents(Attribute[]? attributes) => GetEvents();
+
+ public PropertyDescriptorCollection GetProperties() => PropertyDescriptorCollection.Empty;
+
+ public PropertyDescriptorCollection GetProperties(Attribute[]? attributes) => GetProperties();
+
+ public object? GetPropertyOwner(PropertyDescriptor? pd) => null;
+ }
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object? instance)
+ {
+ return new EmptyPropertyListDescriptor();
+ }
+ }
+
+ [TypeDescriptionProvider(typeof(EmptyPropertiesTypeProvider))]
+ public sealed class TypeWithProperty
+ {
+ public int OneProperty { get; set; }
+ }
+
+ public static IEnumerable<object[]> GetConverter_ByMultithread_ReturnsExpected_TestData()
+ {
+ yield return new object[] { typeof(MyClass), typeof(MyTypeConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithCustomTypeDescriptionProvider), typeof(MyInheritedClassWithCustomTypeDescriptionProviderConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithInheritedTypeDescriptionProvider), typeof(MyTypeConverter) };
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverter_ByMultithread_ReturnsExpected_TestData))]
+ public async void GetConverter_ByMultithread_ReturnsExpected(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 100).Select(_ =>
+ Task.Run(() => TypeDescriptor.GetConverter(typeForGetConverter))));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ public static IEnumerable<object[]> GetConverterWithAddProvider_ByMultithread_Success_TestData()
+ {
+ foreach (object[] currentTestCase in GetConverter_ByMultithread_ReturnsExpected_TestData())
+ {
+ yield return currentTestCase;
+ }
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverterWithAddProvider_ByMultithread_Success_TestData))]
+ public async void GetConverterWithAddProvider_ByMultithread_Success(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 200).Select(_ =>
+ Task.Run(() =>
+ {
+ var mockProvider = new Mock<TypeDescriptionProvider>(MockBehavior.Strict);
+ var someInstance = new object();
+ TypeDescriptor.AddProvider(mockProvider.Object, someInstance);
+ return TypeDescriptor.GetConverter(typeForGetConverter);
+ })));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ [TypeDescriptionProvider(typeof(MyClassTypeDescriptionProvider))]
+ public class MyClass
+ {
+ }
+
+ [TypeDescriptionProvider(typeof(MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider))]
+ public class MyInheritedClassWithCustomTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyInheritedClassWithInheritedTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyClassTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyClassTypeDescriptor();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor();
+ }
+ }
+
+ public class MyClassTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyTypeConverter();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderConverter();
+ }
+ }
+
+ public class MyTypeConverter : TypeConverter
+ {
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderConverter : TypeConverter
+ {
+ }
  }
 }

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TypeDescriptor.cs

@@ -29,6 +29,7 @@ public sealed class TypeDescriptor
  private static readonly WeakHashtable s_providerTable = new WeakHashtable(); // mapping of type or object hash to a provider list
  private static readonly Hashtable s_providerTypeTable = new Hashtable(); // A direct mapping from type to provider.
  private static readonly Hashtable s_defaultProviders = new Hashtable(); // A table of type -> default provider to track DefaultTypeDescriptionProviderAttributes.
+ private static readonly Hashtable s_defaultProvidersChecked = new Hashtable(); // A table similar to s_defaultProviders but only set after providers are checked, in order to reduce locks.
  private static WeakHashtable? s_associationTable;
  private static int s_metadataVersion; // a version stamp for our metadata. Used by property descriptors to know when to rebuild attributes.
 
@@ -262,7 +263,9 @@ public static void AddProviderTransparent(TypeDescriptionProvider provider, obje
  /// </summary>
  private static void CheckDefaultProvider(Type type)
  {
- if (s_defaultProviders.ContainsKey(type))
+ bool providerAdded = false;
+
+ if (s_defaultProvidersChecked.ContainsKey(type))
  {
  return;
  }
@@ -278,26 +281,27 @@ private static void CheckDefaultProvider(Type type)
  // and it starts messing around with type information,
  // this could infinitely recurse.
  s_defaultProviders[type] = null;
- }
 
- // Always use core reflection when checking for
- // the default provider attribute. If there is a
- // provider, we probably don't want to build up our
- // own cache state against the type. There shouldn't be
- // more than one of these, but walk anyway. Walk in
- // reverse order so that the most derived takes precidence.
- object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
-bool providerAdded = false;
-for (int idx = attrs.Length - 1; idx >= 0; idx--)
-{
-TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
-Type? providerType = Type.GetType(pa.TypeName);
-if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
-{
-TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
-AddProvider(prov, type);
-providerAdded = true;
+// Always use core reflection when checking for
+// the default provider attribute. If there is a
+// provider, we probably don't want to build up our
+// own cache state against the type. There shouldn't be
+// more than one of these, but walk anyway. Walk in
+// reverse order so that the most derived takes precedence.
+object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
+ for (int idx = attrs.Length - 1; idx >= 0; idx--)
+ {
+ TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
+ Type? providerType = Type.GetType(pa.TypeName);
+ if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
+ {
+ TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
+ AddProvider(prov, type);
+ providerAdded = true;
+}
  }
+
+ s_defaultProvidersChecked[type] = null;
  }
 
  // If we did not add a provider, check the base class.

src/libraries/System.ComponentModel.TypeConverter/tests/TypeDescriptorTests.cs

@@ -5,6 +5,9 @@
 using System.Collections.Generic;
 using System.ComponentModel.Design;
 using System.Globalization;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 using Moq;
 using Xunit;
 
@@ -1231,5 +1234,196 @@ protected DerivedCultureInfo() : base("hello")
  class TwiceDerivedCultureInfo : DerivedCultureInfo
  {
  }
+
+ private long _concurrentError = 0;
+ private bool ConcurrentError
+ {
+ get => Interlocked.Read(ref _concurrentError) == 1;
+ set => Interlocked.Exchange(ref _concurrentError, value ? 1 : 0);
+ }
+
+ private void ConcurrentTest(TypeWithProperty instance)
+ {
+ var properties = TypeDescriptor.GetProperties(instance);
+ Thread.Sleep(10);
+ if (properties.Count > 0)
+ {
+ ConcurrentError = true;
+ }
+ }
+
+ [SkipOnPlatform(TestPlatforms.Browser, "Thread.Start is not supported on browsers.")]
+ [Fact]
+ public void ConcurrentGetProperties_ReturnsExpected()
+ {
+ const int Timeout = 60000;
+ int concurrentCount = Environment.ProcessorCount * 2;
+
+ using var finished = new CountdownEvent(concurrentCount);
+
+ var instances = new TypeWithProperty[concurrentCount];
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ instances[i] = new TypeWithProperty();
+ }
+
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ int i2 = i;
+ new Thread(() =>
+ {
+ ConcurrentTest(instances[i2]);
+ finished.Signal();
+ }).Start();
+ }
+
+ finished.Wait(Timeout);
+
+ if (finished.CurrentCount != 0)
+ {
+ Assert.Fail("Timeout. Possible deadlock.");
+ }
+ else
+ {
+ Assert.False(ConcurrentError, "Fallback type descriptor is used. Possible race condition.");
+ }
+ }
+
+ public sealed class EmptyPropertiesTypeProvider : TypeDescriptionProvider
+ {
+ private sealed class EmptyPropertyListDescriptor : ICustomTypeDescriptor
+ {
+ public AttributeCollection GetAttributes() => AttributeCollection.Empty;
+
+ public string? GetClassName() => null;
+
+ public string? GetComponentName() => null;
+
+ public TypeConverter? GetConverter() => new TypeConverter();
+
+ public EventDescriptor? GetDefaultEvent() => null;
+
+ public PropertyDescriptor? GetDefaultProperty() => null;
+
+ public object? GetEditor(Type editorBaseType) => null;
+
+ public EventDescriptorCollection GetEvents() => EventDescriptorCollection.Empty;
+
+ public EventDescriptorCollection GetEvents(Attribute[]? attributes) => GetEvents();
+
+ public PropertyDescriptorCollection GetProperties() => PropertyDescriptorCollection.Empty;
+
+ public PropertyDescriptorCollection GetProperties(Attribute[]? attributes) => GetProperties();
+
+ public object? GetPropertyOwner(PropertyDescriptor? pd) => null;
+ }
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object? instance)
+ {
+ return new EmptyPropertyListDescriptor();
+ }
+ }
+
+ [TypeDescriptionProvider(typeof(EmptyPropertiesTypeProvider))]
+ public sealed class TypeWithProperty
+ {
+ public int OneProperty { get; set; }
+ }
+
+ public static IEnumerable<object[]> GetConverter_ByMultithread_ReturnsExpected_TestData()
+ {
+ yield return new object[] { typeof(MyClass), typeof(MyTypeConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithCustomTypeDescriptionProvider), typeof(MyInheritedClassWithCustomTypeDescriptionProviderConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithInheritedTypeDescriptionProvider), typeof(MyTypeConverter) };
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverter_ByMultithread_ReturnsExpected_TestData))]
+ public async void GetConverter_ByMultithread_ReturnsExpected(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 100).Select(_ =>
+ Task.Run(() => TypeDescriptor.GetConverter(typeForGetConverter))));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ public static IEnumerable<object[]> GetConverterWithAddProvider_ByMultithread_Success_TestData()
+ {
+ foreach (object[] currentTestCase in GetConverter_ByMultithread_ReturnsExpected_TestData())
+ {
+ yield return currentTestCase;
+ }
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverterWithAddProvider_ByMultithread_Success_TestData))]
+ public async void GetConverterWithAddProvider_ByMultithread_Success(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 200).Select(_ =>
+ Task.Run(() =>
+ {
+ var mockProvider = new Mock<TypeDescriptionProvider>(MockBehavior.Strict);
+ var someInstance = new object();
+ TypeDescriptor.AddProvider(mockProvider.Object, someInstance);
+ return TypeDescriptor.GetConverter(typeForGetConverter);
+ })));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ [TypeDescriptionProvider(typeof(MyClassTypeDescriptionProvider))]
+ public class MyClass
+ {
+ }
+
+ [TypeDescriptionProvider(typeof(MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider))]
+ public class MyInheritedClassWithCustomTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyInheritedClassWithInheritedTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyClassTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyClassTypeDescriptor();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor();
+ }
+ }
+
+ public class MyClassTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyTypeConverter();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderConverter();
+ }
+ }
+
+ public class MyTypeConverter : TypeConverter
+ {
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderConverter : TypeConverter
+ {
+ }
  }
 }

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TypeDescriptor.cs

@@ -29,6 +29,7 @@ public sealed class TypeDescriptor
  private static readonly WeakHashtable s_providerTable = new WeakHashtable(); // mapping of type or object hash to a provider list
  private static readonly Hashtable s_providerTypeTable = new Hashtable(); // A direct mapping from type to provider.
  private static readonly Hashtable s_defaultProviders = new Hashtable(); // A table of type -> default provider to track DefaultTypeDescriptionProviderAttributes.
+ private static readonly Hashtable s_defaultProvidersChecked = new Hashtable(); // A table similar to s_defaultProviders but only set after providers are checked, in order to reduce locks.
  private static WeakHashtable? s_associationTable;
  private static int s_metadataVersion; // a version stamp for our metadata. Used by property descriptors to know when to rebuild attributes.
 
@@ -262,7 +263,9 @@ public static void AddProviderTransparent(TypeDescriptionProvider provider, obje
  /// </summary>
  private static void CheckDefaultProvider(Type type)
  {
- if (s_defaultProviders.ContainsKey(type))
+ bool providerAdded = false;
+
+ if (s_defaultProvidersChecked.ContainsKey(type))
  {
  return;
  }
@@ -278,26 +281,27 @@ private static void CheckDefaultProvider(Type type)
  // and it starts messing around with type information,
  // this could infinitely recurse.
  s_defaultProviders[type] = null;
- }
 
- // Always use core reflection when checking for
- // the default provider attribute. If there is a
- // provider, we probably don't want to build up our
- // own cache state against the type. There shouldn't be
- // more than one of these, but walk anyway. Walk in
- // reverse order so that the most derived takes precidence.
- object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
-bool providerAdded = false;
-for (int idx = attrs.Length - 1; idx >= 0; idx--)
-{
-TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
-Type? providerType = Type.GetType(pa.TypeName);
-if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
-{
-TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
-AddProvider(prov, type);
-providerAdded = true;
+// Always use core reflection when checking for
+// the default provider attribute. If there is a
+// provider, we probably don't want to build up our
+// own cache state against the type. There shouldn't be
+// more than one of these, but walk anyway. Walk in
+// reverse order so that the most derived takes precedence.
+object[] attrs = type.GetCustomAttributes(typeof(TypeDescriptionProviderAttribute), false);
+ for (int idx = attrs.Length - 1; idx >= 0; idx--)
+ {
+ TypeDescriptionProviderAttribute pa = (TypeDescriptionProviderAttribute)attrs[idx];
+ Type? providerType = Type.GetType(pa.TypeName);
+ if (providerType != null && typeof(TypeDescriptionProvider).IsAssignableFrom(providerType))
+ {
+ TypeDescriptionProvider prov = (TypeDescriptionProvider)Activator.CreateInstance(providerType)!;
+ AddProvider(prov, type);
+ providerAdded = true;
+}
  }
+
+ s_defaultProvidersChecked[type] = null;
  }
 
  // If we did not add a provider, check the base class.

src/libraries/System.ComponentModel.TypeConverter/tests/TypeDescriptorTests.cs

@@ -5,6 +5,9 @@
 using System.Collections.Generic;
 using System.ComponentModel.Design;
 using System.Globalization;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 using Moq;
 using Xunit;
 
@@ -1231,5 +1234,196 @@ protected DerivedCultureInfo() : base("hello")
  class TwiceDerivedCultureInfo : DerivedCultureInfo
  {
  }
+
+ private long _concurrentError = 0;
+ private bool ConcurrentError
+ {
+ get => Interlocked.Read(ref _concurrentError) == 1;
+ set => Interlocked.Exchange(ref _concurrentError, value ? 1 : 0);
+ }
+
+ private void ConcurrentTest(TypeWithProperty instance)
+ {
+ var properties = TypeDescriptor.GetProperties(instance);
+ Thread.Sleep(10);
+ if (properties.Count > 0)
+ {
+ ConcurrentError = true;
+ }
+ }
+
+ [SkipOnPlatform(TestPlatforms.Browser, "Thread.Start is not supported on browsers.")]
+ [Fact]
+ public void ConcurrentGetProperties_ReturnsExpected()
+ {
+ const int Timeout = 60000;
+ int concurrentCount = Environment.ProcessorCount * 2;
+
+ using var finished = new CountdownEvent(concurrentCount);
+
+ var instances = new TypeWithProperty[concurrentCount];
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ instances[i] = new TypeWithProperty();
+ }
+
+ for (int i = 0; i < concurrentCount; i++)
+ {
+ int i2 = i;
+ new Thread(() =>
+ {
+ ConcurrentTest(instances[i2]);
+ finished.Signal();
+ }).Start();
+ }
+
+ finished.Wait(Timeout);
+
+ if (finished.CurrentCount != 0)
+ {
+ Assert.Fail("Timeout. Possible deadlock.");
+ }
+ else
+ {
+ Assert.False(ConcurrentError, "Fallback type descriptor is used. Possible race condition.");
+ }
+ }
+
+ public sealed class EmptyPropertiesTypeProvider : TypeDescriptionProvider
+ {
+ private sealed class EmptyPropertyListDescriptor : ICustomTypeDescriptor
+ {
+ public AttributeCollection GetAttributes() => AttributeCollection.Empty;
+
+ public string? GetClassName() => null;
+
+ public string? GetComponentName() => null;
+
+ public TypeConverter? GetConverter() => new TypeConverter();
+
+ public EventDescriptor? GetDefaultEvent() => null;
+
+ public PropertyDescriptor? GetDefaultProperty() => null;
+
+ public object? GetEditor(Type editorBaseType) => null;
+
+ public EventDescriptorCollection GetEvents() => EventDescriptorCollection.Empty;
+
+ public EventDescriptorCollection GetEvents(Attribute[]? attributes) => GetEvents();
+
+ public PropertyDescriptorCollection GetProperties() => PropertyDescriptorCollection.Empty;
+
+ public PropertyDescriptorCollection GetProperties(Attribute[]? attributes) => GetProperties();
+
+ public object? GetPropertyOwner(PropertyDescriptor? pd) => null;
+ }
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object? instance)
+ {
+ return new EmptyPropertyListDescriptor();
+ }
+ }
+
+ [TypeDescriptionProvider(typeof(EmptyPropertiesTypeProvider))]
+ public sealed class TypeWithProperty
+ {
+ public int OneProperty { get; set; }
+ }
+
+ public static IEnumerable<object[]> GetConverter_ByMultithread_ReturnsExpected_TestData()
+ {
+ yield return new object[] { typeof(MyClass), typeof(MyTypeConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithCustomTypeDescriptionProvider), typeof(MyInheritedClassWithCustomTypeDescriptionProviderConverter) };
+ yield return new object[] { typeof(MyInheritedClassWithInheritedTypeDescriptionProvider), typeof(MyTypeConverter) };
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverter_ByMultithread_ReturnsExpected_TestData))]
+ public async void GetConverter_ByMultithread_ReturnsExpected(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 100).Select(_ =>
+ Task.Run(() => TypeDescriptor.GetConverter(typeForGetConverter))));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ public static IEnumerable<object[]> GetConverterWithAddProvider_ByMultithread_Success_TestData()
+ {
+ foreach (object[] currentTestCase in GetConverter_ByMultithread_ReturnsExpected_TestData())
+ {
+ yield return currentTestCase;
+ }
+ }
+
+ [Theory]
+ [MemberData(nameof(GetConverterWithAddProvider_ByMultithread_Success_TestData))]
+ public async void GetConverterWithAddProvider_ByMultithread_Success(Type typeForGetConverter, Type expectedConverterType)
+ {
+ TypeConverter[] actualConverters = await Task.WhenAll(
+ Enumerable.Range(0, 200).Select(_ =>
+ Task.Run(() =>
+ {
+ var mockProvider = new Mock<TypeDescriptionProvider>(MockBehavior.Strict);
+ var someInstance = new object();
+ TypeDescriptor.AddProvider(mockProvider.Object, someInstance);
+ return TypeDescriptor.GetConverter(typeForGetConverter);
+ })));
+ Assert.All(actualConverters,
+ currentConverter => Assert.IsType(expectedConverterType, currentConverter));
+ }
+
+ [TypeDescriptionProvider(typeof(MyClassTypeDescriptionProvider))]
+ public class MyClass
+ {
+ }
+
+ [TypeDescriptionProvider(typeof(MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider))]
+ public class MyInheritedClassWithCustomTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyInheritedClassWithInheritedTypeDescriptionProvider : MyClass
+ {
+ }
+
+ public class MyClassTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyClassTypeDescriptor();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptionProvider : TypeDescriptionProvider
+ {
+ public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor();
+ }
+ }
+
+ public class MyClassTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyTypeConverter();
+ }
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderTypeDescriptor : CustomTypeDescriptor
+ {
+ public override TypeConverter GetConverter()
+ {
+ return new MyInheritedClassWithCustomTypeDescriptionProviderConverter();
+ }
+ }
+
+ public class MyTypeConverter : TypeConverter
+ {
+ }
+
+ public class MyInheritedClassWithCustomTypeDescriptionProviderConverter : TypeConverter
+ {
+ }
  }
 }