What's the meaning of “UseTaskFriendlySynchronizationContext”?

Question

There is a new app setting in asp.net 4.5

code like this

Answer 1

More details, quoted from ASP.NET 4.5.1 documentation for appSettings on MSDN:

aspnet:UseTaskFriendlySynchronizationContext

Specifies how asynchronous code paths in ASP.NET 4.5 behave.

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If this key value is set to false [default], asynchronous code paths in ASP.NET 4.5 behave as they did in ASP.NET 4.0. If this key value is set to true, ASP.NET 4.5 uses code paths that are optimized for Task-returning APIs. Setting this compatibility switch is mandatory for WebSockets-enabled applications, for using Task-based asynchrony in Web Forms pages, and for certain other asynchronous behaviors.