c# - Interlocked.CompareExchange<Int> using GreaterThan or LessThan instead of equality

Question

The System.Threading.Interlocked object allows for Addition (subtraction) and comparison as an atomic operation. It seems that a CompareExchange that just doesn't do equality but also GreaterThan/LessThan as an atomic comparison would be quite valuable.

Would a hypothetical Interlocked.GreaterThan a feature of the IL or is it a CPU-level feature? Both?

Lacking any other option, is it possible to create such a feature in C++ or direct IL code and expose that functionality to C#?

Answer 1

You can build other atomic operations out of InterlockedCompareExchange.

public static bool InterlockedExchangeIfGreaterThan(ref int location, int comparison, int newValue)
{
    int initialValue;
    do
    {
        initialValue = location;
        if (initialValue >= comparison) return false;
    }
    while (System.Threading.Interlocked.CompareExchange(ref location, newValue, initialValue) != initialValue);
    return true;
}