Category: Personal

This is a little playful MutableWhenAny and MutableWhenAll extension for the Task Parallel Library (TPL), using a ObservableCollection.

The extension makes it possible to add or removed tasks to/from an ObservableCollection<Task> while the MutableWhenAny or MutableWhenAll is used to wait on the tasks in this (mutable) collection.

 https://github.com/okmer/MutableWhen

It’s not super useful in practice, but a nice little exercise that combines two cool C# features into a fun asynchronous “magic” trick.

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Threading;
using System.Threading.Tasks;
 
namespace Com.Okmer.Extensions.ObservableCollectionOfTask
{
    public static class ObservableCollectionOfTaskExtention
    {
        private const int INFINITE = -1;
 
        public static async Task MutableWhenAll(this ObservableCollection<Task> collection)
        {
            await MutableWhenSomething(collection, Task.WhenAll);
        }
 
        public static async Task MutableWhenAny(this ObservableCollection<Task> collection)
        {
            await MutableWhenSomething(collection, Task.WhenAny);
        }
 
        private static async Task MutableWhenSomething(this ObservableCollection<Task> collection, Func<IEnumerable<Task>, Task> whenSomething)
        {
            Task waitAllTask = null;
            Task helperTask = null;
 
            bool isCollectionChanged = false;
 
            do
            {
                //Cancellation on collection changed event
                var cts = new CancellationTokenSource();
                var cancelActionHandler = (sender, arg) => cts.Cancel(false);
                collection.CollectionChanged += cancelActionHandler;
 
                //Current collection
                waitAllTask = whenSomething(collection);
 
                //Wait on current collection or collection changed event
                try
                {
                    helperTask = Task.Delay(INFINITE, cts.Token);
                    await Task.WhenAny(waitAllTask, helperTask);
                }
                finally
                {
                    isCollectionChanged = cts.IsCancellationRequested;
                    cts.Cancel(false);
                    cts.Dispose();
                    collection.CollectionChanged -= cancelActionHandler;
                }
            }
            while (isCollectionChanged);
 
            //Return the WaitAll on collection results
            await waitAllTask;
        }
    }
}

A simple example application that demonstrates the MutableWhenAll extension on an observable collection of tasks. The longest running task is added to the observable collection after MutableWhenAll is called, but the MutableWhenAll will complete only when all tasks (included this longest running task) are completed.

using System;
using System.Collections.ObjectModel;
using System.Threading.Tasks;
 
using Com.Okmer.Extensions.ObservableCollectionOfTask;
 
namespace MutableWhenAllTest
{
    class Program
    {
        static void Main(string[] args)
        {
            ObservableCollection<Task> tasks = new ObservableCollection<Task>();
 
            Task t1 = Task.Run(async () => { await Task.Delay(1000); Console.WriteLine("t1"); });
            Task t2 = Task.Run(async () => { await Task.Delay(2000); Console.WriteLine("t2"); });
            Task t3 = Task.Run(async () => { await Task.Delay(3000); Console.WriteLine("t3"); });
 
            tasks.Add(t1);
            tasks.Add(t2);
 
            Task a1 = tasks.MutableWhenAll();
 
            tasks.Add(t3);
 
            a1.ContinueWith(t =>
            {
                if (t.IsCanceled)
                {
                    Console.WriteLine("Canceled");
                }
 
                if (t.IsFaulted)
                {
                    Console.WriteLine("Faulted");
                }
 
                if (t.IsCompleted)
                {
                    Console.WriteLine("Completed");
                }
            });
 
            a1.Wait();
 
            Console.ReadLine();
        }
 
    }
}

DynamicBag is a toy project that used a Dictionary<string, dynamic> to create a dynamic storage class.

using System;
using System.Collections.Generic;
using System.Runtime.Serialization;
 
namespace Com.Okmer.DynamicTypes
{
    [Serializable]
    public class DynamicBag : Dictionary<string, dynamic>
    {
        public DynamicBag() { }
 
        public DynamicBag(int capacity) : base(capacity) { }
 
        public DynamicBag(IDictionary<string, dynamic> dictionary) : base(dictionary) { }
 
        public DynamicBag(SerializationInfo info, StreamingContext context) : base(info, context) { }
 
        public void ToBinaryFile(string fileName)
        {
            BinarySerialization.ToFile(this, fileName);
        }
 
        public static DynamicBag FromBinaryFile(string fileName)
        {
            return BinarySerialization.FromFile<DynamicBag>(fileName);
        }
    }
}

These DynamicBag(s) can be serialized to and deserialized from a file using BinarySerialization.

using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;
 
namespace Com.Okmer.DynamicTypes
{
    public static class BinarySerialization
    {
        public static void ToFile<T>(T value, string fileName) where T : ISerializable
        {
            IFormatter formatter = new BinaryFormatter();
            using (Stream stream = new FileStream(fileName, FileMode.Create, FileAccess.Write, FileShare.None))
            {
                formatter.Serialize(stream, value);
            }
        }
 
        public static T FromFile<T>(string fileName) where T : ISerializable, new()
        {
            T result = new T();
            IFormatter formatter = new BinaryFormatter();
            using (Stream stream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Read))
            {
                result = (T)formatter.Deserialize(stream);
            }
            return result;
        }
    }
}

The simple example application uses polymorphism to print the content of the DynamicBag(s) to the console.

using System;
using System.Collections.Generic;
 
using Com.Okmer.DynamicTypes;
 
namespace SampleApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            DynamicBag shoppingBag = new DynamicBag();
            DynamicBag spareBag = new DynamicBag();
 
            shoppingBag.Add("spareBag", spareBag);
            shoppingBag.Add("shoppingList", new string[] { "eggs", "milk", "cheese" });
 
            spareBag.Add("carCoin", "50ct");
            spareBag.Add("carValue", 50);
 
            Print(shoppingBag);
 
            Console.Write("---------------------------> ENTER <----: ");
            Console.ReadLine();
 
            shoppingBag.ToBinaryFile("shoppingBag.bin");
 
            DynamicBag shoppingBagFromBinaryFile = DynamicBag.FromBinaryFile("shoppingBag.bin");
 
            Print(shoppingBagFromBinaryFile);
 
            Console.Write("---------------------------> ENTER <----: ");
            Console.ReadLine();
        }
 
        private static void Print(DynamicBag bag)
        {
            Console.WriteLine("BAG BEGIN");
            foreach (string key in bag.Keys)
            {
                Console.WriteLine(key + ": ");
                Print(bag[key]);
            }
            Console.WriteLine("BAG END");
        }
 
        private static void Print(IEnumerable<dynamic> values)
        {
            Console.WriteLine("ENUMERABLE BEGIN");
            foreach (dynamic value in values)
            {
                Print(value);
            }
            Console.WriteLine("ENUMERABLE END");
        }
 
        private static void Print(bool value) => Console.WriteLine("bool -> " + value.ToString());
 
        private static void Print(int value) => Console.WriteLine("int -> " + value.ToString());
 
        private static void Print(double value) => Console.WriteLine("double -> " + value.ToString());
 
        private static void Print(string value) => Console.WriteLine("string -> " + value.ToString());
 
        private static void Print(object value) => Console.WriteLine("object-> " + value.ToString());
    }
}