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wpf-dispatchersynchronizationcontext_createcopy-now-returns-a-new-copy-instead-of-the-current-instance.md

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WPF DispatcherSynchronizationContext.CreateCopy now returns a new copy instead of the current instance

Scope

Minor

Version Introduced

4.5

Source Analyzer Status

Available

Change Description

In the .NET Framework 4, xref:System.Windows.Threading.DispatcherSynchronizationContext.CreateCopy returned a reference to the current instance, primarily as a performance optimization. In the .NET Framework 4.5, it returns a new instance which makes it possible for the first time to conclude that equal references indicate the executing thread is in the correct synchronization context. It is unlikely that code that checks the identity of these references will be affected, but because of the change, code that calls xref:System.Windows.Threading.DispatcherSynchronizationContext.CreateCopy should be tested as part of migration to the .NET Framework 4.5 or newer.

  • Quirked
  • Build-time break

Recommended Action

Be aware that xref:System.Windows.Threading.DispatcherSynchronizationContext.CreateCopy will now return a new xref:System.Threading.SynchronizationContext?displayProperty=name object. Previously, code that used equivalence of references generated this way was not actually checking whether it was in the proper context, but does when built against .NET Framework 4.5 or later. While unlikely to cause issues, exercising the affected code paths should be enough to determine if this poses any problem.

Affected APIs

  • M:System.Windows.Threading.DispatcherSynchronizationContext.CreateCopy

Category

Windows Presentation Foundation (WPF)