Assign threads to task in C#

Question

I have multiple tasks in an array, that are used to compute prime numbers in a given range. To undergo a comparison of tasks vs thread performance, I want to use threads within tasks and then check the performance stats.

How will the threads be used with tasks, so far this is what I have done:

public Form1()
    {
        InitializeComponent();

        cpuCounter = new PerformanceCounter();

        cpuCounter.CategoryName = "Processor";
        cpuCounter.CounterName = "% Processor Time";
        cpuCounter.InstanceName = "_Total";

        ramCounter = new PerformanceCounter("Memory", "Available MBytes");

        this.scheduler = TaskScheduler.FromCurrentSynchronizationContext();

        this.numericUpDown1.Maximum = int.MaxValue;
    }

    private void btnCalculate_Click(object sender, EventArgs e)
    {
        //get the lower and upper bounds for prime range
        int lower = int.Parse(this.numericUpDown1.Value.ToString());
        int upper = 0 ;

        //get the time in milliseconds for task deadline
        int taskDeadline = int.Parse(this.time.Text);

        //determine tasks completed
        int tasksCompleted = 0;

        Random random = new Random();

        for (int taskCount = 1; taskCount <= 1; ++taskCount)
        {
            int taskArraySize = taskCount * 100;
            Task[] taskArray = new Task[taskArraySize];

            this.txtNumOfPrimes.Text += "Performing test for " +  
                 taskArraySize.ToString() + 
                 " tasks" + 
                 Environment.NewLine + 
                 Environment.NewLine; 

            for (int i = 0; i < taskArray.Length; i++)
            {
                upper = random.Next(5, 10);
                taskArray[i] = new Task(() => getPrimesInRange(lower, upper));
                taskArray[i].Start();

                bool timeout = taskArray[i].Wait(taskDeadline);

                if (!timeout)
                {
                    // If it hasn't finished at timeout display message
                    this.txtNumOfPrimes.Text += 
                        "Message to User: Task not completed, Status=> " + 
                        taskArray[i].Status.ToString() + 
                        Environment.NewLine;

                }

                else
                {
                    this.txtNumOfPrimes.Text += "Task completed in timeout " + 
                         ", CPU usage: " + this.getCurrentCpuUsage() + 
                         ", RAM usage: " + 
                         this.getAvailableRAM() + 
                         Environment.NewLine;

                    tasksCompleted++;
                }
            }
        }



        this.txtNumOfPrimes.Text += Environment.NewLine;
        this.txtNumOfPrimes.Text += 
            "Tasks Completed: " + 
            tasksCompleted.ToString() + 
            Environment.NewLine;
    }

Answer 1

The whole point of tasks is "simplifying the process of adding parallelism and concurrency to applications". Indeed (from http://msdn.microsoft.com/en-us/library/dd537609):

Behind the scenes, tasks are queued to the ThreadPool, which has been enhanced with algorithms (like hill-climbing) that determine and adjust to the number of threads that maximizes throughput. This makes tasks relatively lightweight, and you can create many of them to enable fine-grained parallelism. To complement this, widely-known work-stealing algorithms are employed to provide load-balancing.

In short, tasks do the thread work without much of the hassle and legwork.

To compare the two, consider using Parrallel.ForEach for tasks. For example:

public class PrimeRange
{
    public int Start;
    public int Snd;
}

List<PrimeRange> primes = new []
{
    new PrimeRange{Start = 0, End = 1000},
    new PrimeRange{Start = 1001, End = 2000}
    // An so on
};
Parallel.ForEach(primes, x => CalculatePrimes(x, OnResult())));

where CalculatePrimes is a method that takes a PrimeRange and a delegate to call when the primes have been calculated. Parraler.ForEach will start a task for each element of primes and run CalculatePrimes() on it and handle the thread assignment and scheduling for you.

To compare it to threads, use something like:

List<Thread> threads = new List<Thread>();
foreach(PrimeRange primeRange in primes)
{
    threads = new Thread(CalculatePrimes).Start(x);
}
foreach(var thread in threads)
{
    thread.Join();
}    

where CalculatePrimes would need to also store the results (or something similar). See C# Waiting for multiple threads to finish for more information about waiting on running threads.

You could time the results using a StopWatch.