Why my tasks won't run in c# console application?

Question

I have made a simple Producer-Consumer console application, where there are two consumers and 1 producer. I am checking whether some random numbers are divisible by 3 or 5.

Here is the code:

using System;
using System.Collections.Concurrent;
using System.Threading.Tasks;

namespace ProducerConsumer
{
    class Program
    {
        public class OneProducerTwoConsumer
        {
            private readonly BlockingCollection<int> randomNumbersForDivisibleByFive = new BlockingCollection<int>(10);
            private readonly BlockingCollection<int> randomNumbersForDivisibleByThree = new BlockingCollection<int>(10);

            private int numberOfDivisibleByFive = 0;
            private int numberOfDivisibleByThree = 0;

            private void Producer()
            {
                int numberOfNumbers = 50;
                Random random = new Random();

                for (int i = 0; i < numberOfNumbers; i++)
                {
                    var randomNumber = random.Next();

                    randomNumbersForDivisibleByFive.Add(randomNumber);
                    randomNumbersForDivisibleByThree.Add(randomNumber);
                }
            }

            private void ConsumerDivisibleByFive()
            {
                foreach (int randomNumber in randomNumbersForDivisibleByFive.GetConsumingEnumerable())
                {
                    if(randomNumber % 5 == 0)
                    {
                        numberOfDivisibleByFive++;
                        Console.WriteLine($"{randomNumber} is divisible by 5");
                    }
                    else
                    {
                        Console.WriteLine($"{randomNumber} is not divisible by 5");
                    }
                }

                Console.WriteLine($"There are {numberOfDivisibleByFive} numbers divisible by 5 generated from the producer");
            }

            private void ConsumerDivisibleByThree()
            {
                foreach (int randomNumber in randomNumbersForDivisibleByThree.GetConsumingEnumerable())
                {
                    if (randomNumber % 3 == 0)
                    {
                        numberOfDivisibleByThree++;
                        Console.WriteLine($"{randomNumber} is divisible by 3");
                    }
                    else
                    {
                        Console.WriteLine($"{randomNumber} is not divisible by 3");
                    }
                }

                Console.WriteLine($"There are {numberOfDivisibleByThree} numbers divisible by 3 generated from the producer");
            }

            public void RunTasks()
            {
                var producingTask = Task.Run(() => Producer());

                var divisibleByFiveTask = Task.Run(() => ConsumerDivisibleByFive());

                var divisibleByThreeTask = Task.Run(() => ConsumerDivisibleByThree());

                producingTask.Start();
                divisibleByFiveTask.Start();
                divisibleByThreeTask.Start();
            }
        }

        public static void Main(string[] args)
        {
            OneProducerTwoConsumer oneProducerTwoConsumer = new OneProducerTwoConsumer();
            oneProducerTwoConsumer.RunTasks();
        }
    }
}

However, when I run the code nothing appears on the console and I see nothing wrong with my code.

Any help appreciated!

Answer 1

Change this:

public void RunTasks()
{
    var producingTask = Task.Run(() => Producer());

    var divisibleByFiveTask = Task.Run(() => ConsumerDivisibleByFive());

    var divisibleByThreeTask = Task.Run(() => ConsumerDivisibleByThree());

    producingTask.Start();
    divisibleByFiveTask.Start();
    divisibleByThreeTask.Start();

}

To this:

public void RunTasks()
{
    var producingTask = Task.Run(() => Producer());

    var divisibleByFiveTask = Task.Run(() => ConsumerDivisibleByFive());

    var divisibleByThreeTask = Task.Run(() => ConsumerDivisibleByThree());

    Task.WaitAll(producingTask, divisibleByFiveTask, divisibleByThreeTask);
    
    // or:
    // Task.WhenAll(producingTask, divisibleByFiveTask, divisibleByThreeTask).GetAwaiter().GetResult();
}

When you execute Task.Run(), the task is off and running. Executing their Start method has no effect on what you are doing.

As for the fix: By "waiting" for the tasks to finish, you allow the tasks to complete before the program exits.