FasterThreadLocal<T>.InitializeThread isn't thread-safe. It is being called in LightEpoch.Acquire and can lead to concurrency issues.

Fixed as follows:

            if (values == null)
            {
                Interlocked.CompareExchange(ref values, new T[kMaxInstances], null);
            }

Can you explain how the current implementation of FastThreadLocal<T> is instance specific? I am confused because the values array is thread static which I suppose means that two objects of FastThreadLocal<int> access the same values array if done from the same thread.

FastThreadLocal has a thread-static array, i.e., each thread sees its own copy of the array. Each instance of the object (regardless of threads) will correspond to a unique entry offset (id) in the array. You can visualize this as a 2-d matrix of threads and instances, with one array per thread.

FasterThreadLocal<T>.InitializeThread isn't thread-safe. It is being called in LightEpoch.Acquire and can lead to concurrency issues.

Fixed as follows:

            if (values == null)
            {
                Interlocked.CompareExchange(ref values, new T[kMaxInstances], null);
            }

Why is this necessary for a thread static variable? Won't each thread sees a different copy of "values", making the Interlocked operation unnecessary?

FasterThreadLocal<T>.InitializeThread isn't thread-safe. It is being called in LightEpoch.Acquire and can lead to concurrency issues.

Fixed as follows:

            if (values == null)
            {
                Interlocked.CompareExchange(ref values, new T[kMaxInstances], null);
            }

Why is this necessary for a thread static variable? Won't each thread sees a different copy of "values", making the Interlocked operation unnecessary?

Correct, it's not needed. My original code is fine, I think.