Parallel modification of double [] [] elements without blocking

Question

I have a gear array double[][]that can be modified simultaneously by multiple threads. I would like to make it thread safe, but if possible without locks. Streams can be well oriented on the same element in the array, so the whole problem arises. I found code to increase double-digit values ​​using the method Interlocked.CompareExchange: Why is there no overload of Interlocked.Add that takes paired numbers as parameters?

My question is: will it remain atomic if Interlocked.CompareExchangethere is a reference to an uneven array? Your understanding is greatly appreciated.

Example:

    public class Example
    {
        double[][] items;

        public void AddToItem(int i, int j, double addendum)
        {
            double newCurrentValue = items[i][j];
            double currentValue;
            double newValue;
            SpinWait spin = new SpinWait();

            while (true) {
               currentValue = newCurrentValue;
               newValue = currentValue + addendum;
               // This is the step of which I am uncertain:
               newCurrentValue = Interlocked.CompareExchange(ref items[i][j], newValue, currentValue);
               if (newCurrentValue == currentValue) break;
               spin.SpinOnce();
            }
        }
    }

Answer 1

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:

double newCurrentValue = items[i][j];

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Answer 2

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public class Example
{
    double[][] items;

    public void AddToItem(int i, int j, double addendum)
    {
        var spin = new SpinWait();

        while (true)
        {
            var valueAtStart = Volatile.Read(ref items[i][j]);
            var newValue = valueAtStart + addendum;

            var oldValue = Interlocked.CompareExchange(ref items[i][j], newValue, valueAtStart);

            if (oldValue.Equals(valueAtStart))
                break;
            spin.SpinOnce();
        }
    }
}

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( Interlocked.CompareExchange), items[i][j] Volatile.Read.

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