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:

	public class Example
	{
	[ThreadStatic]
	static int calls = 0;
	}

view raw ThreadStatic.cs hosted with ❤ by GitHub

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

	public class Example
	{
	// Thread-Local variable that yields a name for a thread
	ThreadLocal<string> ThreadName = new ThreadLocal<string>(() =>
	{
	return "Thread" + Thread.CurrentThread.ManagedThreadId;
	});
	}

view raw ThreadLocal.cs hosted with ❤ by GitHub