Runtime Changes for Migration from .NET Framework 4.5 to 4.5.1

Introduction

Runtime changes affect all apps that are running under a .NET Framework it was not compiled against and that use a particular feature.

In the topics that describe runtime changes, we have classified individual items by their expected impact, as follows:

Major This is a significant change that affects a large number of apps or that requires substantial modification of code.

Minor This is a change that affects a small number of apps or that requires minor modification of code.

Edge case This is a change that affects apps under very specific scenarios that are not common.

Transparent This is a change that has no noticeable effect on the app's developer or user. The app should not require modification because of this change.

If you are migrating from the .NET Framework 4.5 to 4.5.1, review the following topics for application compatibility issues that may affect your app:

ADO.NET

ADO.NET now attempts to automatically reconnect broken SQL connections

Details Beginning in the .NET Framework 4.5.1, the .NET Framework will attempt to automatically reconnect broken SQL connections. Although this will typically make apps more reliable, there are edge cases in which an app needs to know that the connection was lost so that it can take some action upon reconnection.
Suggestion If this feature is undesirable due to compatibility concerns, it can be disabled by setting the ConnectRetryCount property of a connection string (or SqlConnectionStringBuilder) to 0.
Scope Edge
Version 4.5.1
Type Runtime
Affected APIs

Core

A ConcurrentDictionary serialized in .NET Framework 4.5 with NetDataContractSerializer cannot be deserialized by .NET Framework 4.5.1 or 4.5.2

Details Due to internal changes to the type, ConcurrentDictionary<TKey,TValue> objects that are serialized with the .NET Framework 4.5 using the NetDataContractSerializer cannot be deserialized in the .NET Framework 4.5.1 or in the .NET Framework 4.5.2.Note that moving in the other direction (serializing with the .NET Framework 4.5.x and deserializing with the .NET Framework 4.5) works. Similarly, all 4.x cross-version serialization works with the .NET Framework 4.6.Serializing and deserializing with a single version of the .NET Framework is not affected.
Suggestion If it is necessary to serialize and deserialize a ConcurrentDictionary<TKey,TValue> between the .NET Framework 4.5 and .NET Framework 4.5.1/4.5.2, an alternate serializer like the DataContractSerializer or BinaryFormatter serializer should be used instead of the NetDataContractSerializer.Alternatively, because this issue is addressed in the .NET Framework 4.6, it may be solved by upgrading to that version of the .NET Framework.
Scope Minor
Version 4.5.1
Type Runtime

ConcurrentQueue<T>.TryPeek can return an erroneous null via its out parameter

Details In some multi-threaded scenarios, TryPeek(T) can return true, but populate the out parameter with a null value (instead of the correct, peeked value).
Suggestion This issue is fixed in the .NET Framework 4.5.1. Upgrading to that Framework will solve the issue.
Scope Major
Version 4.5
Type Runtime
Affected APIs

COR_PRF_GC_ROOT_HANDLEs are not being enumerated by profilers

Details In the .NET Framework v4.5.1, the profiling API RootReferences2() is incorrectly never returning COR_PRF_GC_ROOT_HANDLE (they are returned as COR_PRF_GC_ROOT_OTHER instead). This issue is fixed beginning in the .NET Framework 4.6.
Suggestion This issue has been fixed in the .NET Framework 4.6 and may be addressed by upgrading to that version of the .NET Framework.
Scope Minor
Version 4.5.1
Type Runtime

Deserialization of objects across appdomains can fail

Details In some cases, when an app uses two or more app domains with different application bases, trying to deserialize objects in the logical call context across app domains throws an exception.
Suggestion See Mitigation: Deserialization of Objects Across App Domains
Scope Edge
Version 4.5.1
Type Runtime

EventListener truncates strings with embedded nulls

Details EventListener truncates strings with embedded nulls. Null characters are not supported by the EventSource class. The change only affects apps that use EventListener to read EventSource data in process and that use null characters as delimiters.
Suggestion EventSource data should be updated, if possible, to not use embedded null characters.
Scope Edge
Version 4.5.1
Type Runtime
Affected APIs

EventSource.WriteEvent impls must pass WriteEvent the same parameters that it received (plus ID)

Details The runtime now enforces the contract that specifies the following: A class derived from EventSource that defines an ETW event method must call the base class EventSource.WriteEvent method with the event ID followed by the same arguments that the ETW event method was passed.
Suggestion An IndexOutOfRangeException exception is thrown if an EventListener reads EventSource data in process for an event source that violates this contract.
Scope Minor
Version 4.5.1
Type Runtime

Marshal.SizeOf and Marshal.PtrToStructure overloads break dynamic code

Details Beginning in the .NET Framework 4.5.1, dynamically binding to the methods SizeOf<T>(), SizeOf<T>(T), PtrToStructure(IntPtr, Object), PtrToStructure(IntPtr, Type), PtrToStructure<T>(IntPtr), or PtrToStructure<T>(IntPtr, T), (via Windows PowerShell, IronPython, or the C# dynamic keyword, for example) can result in MethodInvocationExceptions because new overloads of these methods have been added that may be ambiguous to the scripting engines.
Suggestion Update scripts to clearly indicate which overload should be used. This can typically done by explicitly casting the methods' type parameters as Type. See this link for more detail and examples of how to workaround the issue.
Scope Minor
Version 4.5.1
Type Runtime

Some .NET APIs cause first chance (handled) EntryPointNotFoundExceptions

Details In the .NET Framework 4.5, a small number of .NET methods began throwing first chance EntryPointNotFoundExceptions. These exceptions were handled within the .NET Framework, but could break test automation that did not expect the first chance exceptions. These same APIs break some ApiVerifier scenarios when HighVersionLie is enabled.
Suggestion This bug can be avoided by upgrading to .NET Framework 4.5.1. Alternatively, test automation can be updated to not break on first-chance EntryPointNotFoundExceptions.
Scope Edge
Version 4.5
Type Runtime
Affected APIs

WinRT stream adapters no long call FlushAsync automatically on close

Details In Windows Store apps, Windows Runtime stream adapters no longer call the FlushAsync method from the Dispose method.
Suggestion This change should be transparent. Developers can restore the previous behavior by writing code like this:
using (var stream = GetWindowsRuntimeStream() as Stream)
{
// do something
await stream.FlushAsync();
}
Scope Transparent
Version 4.5.1
Type Runtime

Data

ADO.NET now attempts to automatically reconnect broken SQL connections

Details Beginning in the .NET Framework 4.5.1, the .NET Framework will attempt to automatically reconnect broken SQL connections. Although this will typically make apps more reliable, there are edge cases in which an app needs to know that the connection was lost so that it can take some action upon reconnection.
Suggestion If this feature is undesirable due to compatibility concerns, it can be disabled by setting the ConnectRetryCount property of a connection string (or SqlConnectionStringBuilder) to 0.
Scope Edge
Version 4.5.1
Type Runtime
Affected APIs

Serialization

NetDataContractSerializer fails to deserialize a ConcurrentDictionary serialized with a different .NET version

Details By design, the NetDataContractSerializer can be used only if both the serializing and deserializing ends share the same CLR types. Therefore, it is not guaranteed that an object serialized with one version of the .NET Framework can be deserialized by a different version.ConcurrentDictionary<TKey,TValue> is a type that is known to not to deserialize correctly if serialized with the .NET Framework 4.5 or earlier and deserialized with the .NET Framework 4.5.1 or later.
Suggestion There are a number of possible work-arounds for this issue:
Scope Minor
Version 4.5.1
Type Runtime
Affected APIs

Windows Communication Foundation (WCF)

MinFreeMemoryPercentageToActiveService is now respected

Details This setting establishes the minimum memory that must be available on the server before a WCF service can be activated. It is designed to prevent OutOfMemoryException exceptions. In the .NET Framework 4.5, this setting had no effect. In the .NET Framework 4.5.1, the setting is observed.
Suggestion An exception occurs if the free memory available on the web server is less than the percentage defined by the configuration setting. Some WCF services that successfully started and ran in a constrained memory environment may now fail.
Scope Minor
Version 4.5.1
Type Runtime

Windows Presentation Foundation (WPF)

Scrolling a WPF TreeView or grouped ListBox in a VirtualizingStackPanel can cause a hang

Details In the .NET Framework v4.5, scrolling a WPF TreeView in a virtualized stack panel can cause hangs if there are margins in the viewport (between the items in the TreeView, for example, or on an ItemsPresenter element). Additionally, in some cases, different sized items in the view can cause instability even if there are no margins.
Suggestion This bug can be avoided by upgrading to .NET Framework 4.5.1. Alternatively, margins can be removed from view collections (like TreeViews) within virtualized stack panels if all contained items are the same size.
Scope Major
Version 4.5
Type Runtime
Affected APIs