Wednesday, August 13, 2014

Impress your colleagues with your knowledge about... ThreadLocal

Sometimes when working with .NET you discover some hidden gems. Some of them very useful, other ones a little bit harder to find a good way to benefit from their functionality. One of those hidden gems that I discovered some days ago is the ThreadLocal class.

For a long time I’m using the [ThreadStatic] attribute in .NET. It allows you in an easy way to create static variables scoped on a per thread basis. Using it is easy, it is simply a matter of decorating a static field with the [ThreadStatic] attribute:

As mentioned by Jon Skeet, using ThreadStatic has some disadvantages:

  • The variable must be static
  • You have to call the initialization logic yourself
  • Limited PCL support

.NET 4.5 introduces another class that solves the same problem: ThreadLocal.

It offers the same functionality as the ThreadStatic attribute but does not have its disadvantages:

  • The variable doesn’t have to be static
  • You can specify an initialization delegate to be executed on first use in any particular thread (similar in the way you initialize Lazy<T>)
  • The intent is more clear

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