TPL - Parallel with Thread Local Variable

Scenario:

Process data in parallel and store data for each thread in a local variable and then keep adding it to class local variable in thread safe.

Solution:

Use thread-local variables to store and retrieve state in each separate task that is created by a for loop.

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public class ParallelWithThreadLocalVariable
    {
        static void Main(string[] args)
        {
            var rnd = new Random();

            int[] count = Enumerable.Range(0, 1000).ToArray();
            long totalCount = 0;

            //() => 0 initializes the thread-local variable to zero.
            //j: loop counter
            //loop: ParallelLoopState
            //subtotal: thread-local variable (returned by lambda expression)
            Parallel.For<long>(0, count.Length, () => 0, (j, loop, subtotal) =>
            {
                int delay;
                lock (rnd)
                    delay = rnd.Next(1, 1000);
                Thread.Sleep(delay);

                if (loop.ShouldExitCurrentIteration)
                {
                    // if break has been called then any thread processing j > 500 will be called.
                    if (loop.LowestBreakIteration < j)
                        return subtotal;
                }

                if (j == 100)
                {
                    Console.WriteLine($"Breaking at {j}");
                    loop.Break();
                }

                subtotal += count[j];
                return subtotal;
            },
            //called  after all the iterations on a thread have completed.
                (x) => Interlocked.Add(ref totalCount, x)
            );

            Console.WriteLine($"{totalCount}");
            Console.ReadLine();
        }
    }