Description of Preview of Quality Rollup for .NET Framework 4.6, 4.6.1, 4.6.2, 4.7 and 4.7.1 for Windows 7 SP1 and Server 2008 R2 SP1 and for .NET Framework 4.6 for Server 2008 (KB 4096234)

CLR¹

• Fixes an issue in WindowsIdentity.Impersonate in which handles were not being explicitly cleaned up.
• Fixes an issue in deserialization that occurs when a CultureAwareComparer is used by a collection type, for example, a ConcurrentDictionary.
• Fixes an issue in a floating-point overflow in the thread pool’s hill-climbing algorithm.
• Fixes an issue in which you observe high CPU usage that is consumed by ntoskrnl!KiPageFault and that originates from BGC (indicated by clr!*gc_heap::bgc_thread_function), you might want this change so that the GC process no longer uses the system-implemented write watch to track BGC heap modifications. Such usage is very expensive because each of these page faults must take a process-wide lock. This is especially noticeable in recent versions of the system. You are probably seeing that most of the CPU is spent in the ntoskrnl!ExpWaitForSpinLockExclusiveAndAcquire function. This change makes GC use the CLR implementation of write watch instead.

NCL²

• Fixes an issue in the connection limit that occurs when you use HttpClient to send requests to loopback addresses. For more information, see this .NET blog article.

WPF³

• Fixes an issue in which a crash can occur during the shutdown of an application that hosts WPF content in a separate AppDomain. (For example, an Office application that hosts a VSTO add-in that uses WPF.)
• Fixes an issue that causes XAML Browser Applications (XBAPs) that target .NET 3.5 to sometimes be loaded by incorrectly using .NET 4.x runtime.
  
  The fix for this issue must be enabled by customers who have difficulty running XBAP applications that target .NET Framework 3.5 under CLR v4. The fix can be enabled by setting the registry subkey values in the following table.
   

  Platform architecture	Registry subkey	Value name	Value type	Value	Description
  32-bit	HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\Windows Presentation Foundation\Hosting	DoNotLaunchVersion3HostedApplicationInVersion4Runtime	REG_DWORD	0, or value does not exist	XBAP applications that target .NET Framework 3.5 or.NET Framework 4.x will be both launched under CLR v4
  				1, or any non-zero value	XBAP applications that target .NET Framework 3.5 will be launched under CLR v2, and XBAP applications that target .NET Framework 4.x will be launched under CLR v4
  64-bit	Both of these subkeys should be set: Subkey 1 HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\.NETFramework\Windows Presentation Foundation\Hosting Subkey 2 HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\Windows Presentation Foundation\Hosting	DoNotLaunchVersion3HostedApplicationInVersion4Runtime	REG_DWORD	0, or value does not exist	XBAP applications that target .NET Framework 3.5 or.NET Framework 4.x will be both launched under CLR v4
  				1, or any non-zero value	XBAP applications that target .NET Framework 3.5 will be launched under CLR v2, and XBAP applications that target .NET Framework 4.x will be launched under CLR

    
• Fixes an issue in which a WPF application can crash because of a NullReferenceException if a Binding (or MultiBinding) that is used in a DataTrigger (or MultiDataTrigger) that belongs to a Style (or Template or ThemeStyle) reports a new value, but whose host element gets collected during a very narrow period in the reporting process.
• Fixes an issue in which a WPF application can crash because of a spurious ElementNotAvailableException. This can occur when you do the following steps:

1. Change TreeView.IsEnabled
2. Remove an item X from the collection
3. Re-insert the same item X back into the collection
4. Remove one of X's subitems Y from its collection

Note Step 4 can occur at any time relative to steps 2 and 3. However, step 4 must occur after step 1. Steps 2–4 must occur before the asynchronous call to UpdatePeer, posted by step 1. This will occur if steps 2–4 all occur in the same button-click handler.