How to implement a TaskScheduler in C#?

2 years ago
Isabella Edwards
2 minutes

In C#, the TaskScheduler class from System.Threading.Tasks can be used to implement a task scheduler. Below is an example code that demonstrates how to create and schedule tasks.

Firstly, we need to create a custom task scheduler class that inherits from TaskScheduler. In this class, we need to override the QueueTask method to add tasks to the task queue, and override the TryExecuteTaskInline method to execute tasks.

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

public class CustomTaskScheduler : TaskScheduler
{
    private BlockingCollection<Task> taskQueue = new BlockingCollection<Task>();
    private Thread schedulerThread;

    public CustomTaskScheduler()
    {
        schedulerThread = new Thread(RunScheduler);
        schedulerThread.Start();
    }

    protected override IEnumerable<Task> GetScheduledTasks()
    {
        return taskQueue.ToArray();
    }

    protected override void QueueTask(Task task)
    {
        taskQueue.Add(task);
    }

    protected override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
    {
        if (Thread.CurrentThread == schedulerThread)
        {
            return TryExecuteTask(task);
        }
        else
        {
            return false;
        }
    }

    private void RunScheduler()
    {
        foreach (var task in taskQueue.GetConsumingEnumerable())
        {
            TryExecuteTask(task);
        }
    }
}

Next, we can use a custom task scheduler to create and schedule tasks. In the following example, we create 10 tasks and submit them to the custom task scheduler using the Task.Factory.StartNew method.

using System;
using System.Threading.Tasks;

class Program
{
    static void Main()
    {
        CustomTaskScheduler scheduler = new CustomTaskScheduler();

        for (int i = 0; i < 10; i++)
        {
            int taskNumber = i + 1;
            Task.Factory.StartNew(() => DoWork(taskNumber), CancellationToken.None, TaskCreationOptions.None, scheduler);
        }

        Console.ReadKey();
    }

    static void DoWork(int taskNumber)
    {
        Console.WriteLine("Task {0} is executing on thread {1}", taskNumber, Thread.CurrentThread.ManagedThreadId);
    }
}

In the above code, we created 10 tasks and submitted them to a custom task scheduler using the Task.Factory.StartNew method. Each task will print out its task number and thread number.

Please note that the task scheduler schedules tasks in order, so tasks may be executed on different threads, but their order is guaranteed.

I hope this helps you!

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