How to combine all values from a ThreadLocal<T>?

Question

I've run across .NET 4's ThreadLocal<T> and was wondering if there's a way to accumulate the .Value values from all threads.

In Microsoft's ppl C++ library they have Concurrency::combinable::combine_each, is there an equivalent method for .NET's ThreadLocal?

ThreadLocal<long> ticks = new ThreadLocal<long>();

void AddTicks(StopWatch sw)
{
    ticks.Value += sw.ElapsedTicks;
}

void ReportTimes()
{
    long totalTicks = /* How do I accumulate all the different values?  */;
    Console.WriteLine(TimeSpan.FromTicks(totalTicks));
}

Answer 1

Since .NET 4.5, Microsoft added an attribute called Values to the ThreadLocal class that does exactly what you need. Here's the way it works:

var localResult = new ThreadLocal<int>(() => 0, trackAllValues: true);
Parallel.For(0, 10000, i =>
{
    localResult.Value += Compute(i);
});

int result = localResult.Values.Sum();

The code above was obtained from the blog post: New in .NET 4.5: ThreadLocal.Values

Answer 2

This information is not available in .NET 4.0. For 4.5 and up, see Joao's answer.

Microsoft is considering adding such a feature. You will need to write a wrapper around ThreadLocal<T> to add this behavior.

Here is a blog post that gives some directions about how to write a wrapper.