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c#arraysmultithreading
PlaTyPuS
PlaTyPuS

Reputation: 385

C# Increment array values by 1 using 2 threads?

If you have the following problem to solve, how would you do it?

The goal is to create an array of 1000 integer values, initialized to 0 and then increment all the values using 2 threads, each thread will increment each array value by 1.

I did it with the following code but I'm really not sure my solution is ok...

static async Task Main(string[] args)
        {
            var count = 100;
            int[] array = new int[count];
            Array.Clear(array, 0, array.Length);

            await Task.WhenAll(IncrementArray(array, "Task 1"), IncrementArray(array, "Task 2"));
            Array.ForEach(array, Console.WriteLine);
        }

        static object obj = new object();

        static async Task IncrementArray(int[] array, string taskName)
        {
            for (var i = 0; i < array.Length; i++)
            {
                Console.WriteLine(taskName);
                await Task.Delay(100);
                lock (obj)
                {
                    array[i]++;
                }
            }
        }

Thanks for your help!

Upvotes: 0

Views: 446

Answers (2)

ganchito55
ganchito55

Reputation: 3607

You should use Interlocked.Increment that is like ++ but atomic to increse the value in one unit, keeping it thread safe

Upvotes: 0

Nick
Nick

Reputation: 5042

Your solution is not OK. You have a race condition, i.e. the two threads may try to increment one element simultaneously and then produce incorrect results - an element of the array may remain 1, for example.

See Interlocked class, and also lock keyword.

Upvotes: 1

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