What is a Task in C# ?

• What is a Task in C# ?
• Properties of Task class
• Different Methods in Task class
• How to create a Task in C#?
• Return a Value from Task
• Attaching Child Task to Parent Task
• Task Factory

What is a Task in C# ?

.net framework provides System.Threading.Tasks.Task class to let you create threads and run them asynchronously.

Queuing a work item to a thread pool is useful, but there is no way to know when the operation has finished and what the return value is.

So thats the reason Microsoft Introduced the concept of Task.

Task is an object that represents some work that should be done.

The Task can tell you if the work is completed and if the operation returns a result, the Task gives you the result.

Properties of Task Class:

Property	Description
Exception	Returns any exceptions that caused the task to end early
Status	Returns the Tasks status
IsCancelled	Returns true if the Task was cancelled
IsCompleted	Returns true if the task is completed successfully
IsFaulted	Returns true if the task is stopped due to unhandled exception
Factory	Provides acess to TaskFactory class. You can use that to create Tasks

Methods in Task Class :

Methods	Purpose
ConfigureAwait	You can use Await keyword for the Task to complete
ContinueWith	Creates continuation tasks.
Delay	Creates a task after specified amount of time
Run	Creates a Task and queues it to start running
RunSynchronously	Runs a task Synchronously
Start	Starts a task
Wait	Waits for the task to complete
WaitAll	Waits until all tasks are completed
WaitAny	Waits until any one of the tasks in a set completes
WhenAll	Creates a Task that completes when all specified tasks are completed
WhenAny	Creates a Task that completes when any specified tasks completes

How to Create and start a Task in C# :

Let’s look at an example to understand it better.

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using System; using System.Threading.Tasks; namespace TaskExample { public static class TaskProgram {     public static void Main()         {             Task t = Task.Run(() =>               {             for (int x = 0; x < 50; x++)             {             Console.Write("Hi ");             }             });             t.Wait();         }   } }

In the above example, we have created a Task and started it.It waits till the Task is finished before exiting the application.

The wait method is similar to join method in Threads.

Output:

It will print “Hi” 50 times to the console.

How to Return a Value from a Task?

The .NET Framework also has the Task class that you can use if you want a Task should return a value.

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using System; using System.Threading.Tasks;   namespace TaskExample {     public static class TaskProgram     {         public static void Main()         {             Task t = Task.Run(() =>             {                 return 100;             });             Console.WriteLine(t.Result); // Displays 100         }     } }

In the above example, The Task will return 100 and print 100 in console.

Output:

How to attach a child task to parent task?

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using System; using System.Threading.Tasks;   namespace TaskExample { public static class TaskProgram     {     public static void Main()             {                 Task<Int32[] > parent = Task.Run(() =>                     {                     var results = new Int32[3];                     new Task(() => results[0] = 0,                     TaskCreationOptions.AttachedToParent).Start();                     new Task(() => results[1] = 1,                     TaskCreationOptions.AttachedToParent).Start();                     new Task(() => results[2] = 2,                     TaskCreationOptions.AttachedToParent).Start();                     return results;                     });                     var finalTask = parent.ContinueWith(                     parentTask => {                     foreach(int i in parentTask.Result)                     Console.WriteLine(i);                     });                 finalTask.Wait();             }     } }

The finalTask runs only after the parent Task is finished, and the parent Task finishes when all three children are finished

Task Factory :

In above example, you had to create three tasks all with same options.

So you can use TaskFactory to make it easier.You can create TaskFactory with certien configurations and then create Tasks.

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using System.Threading.Tasks; namespace TaskExample {     public static class TaskProgram     {         public static void Main()         {             Task<Int32[]> parent = Task.Run(() =>             {                 var results = new Int32[3];                 TaskFactory tf = new TaskFactory(TaskCreationOptions.AttachedToParent,                 TaskContinuationOptions.ExecuteSynchronously);                 tf.StartNew(() => results[0] = 0);                 tf.StartNew(() => results[1] = 1);                 tf.StartNew(() => results[2] = 2);                 return results;             });             var finalTask = parent.ContinueWith(             parentTask =>             {                 foreach (int i in parentTask.Result)                     Console.WriteLine(i);             });             finalTask.Wait();         }     } }

You can use, wait method to wait on single task. Also WaitAll to wait for multiple tasks to finish.

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using System; using System.Threading; using System.Threading.Tasks;   namespace TaskExample { public static class TaskProgram {     public static void Main()         {         Task[] tasks = new Task[3];         tasks[0] = Task.Run(() => {         Thread.Sleep(1000);         Console.WriteLine('1');         return 1;         });         tasks[1] = Task.Run(() => {         Thread.Sleep(1000);         Console.WriteLine('2');         return 2;         });         tasks[2] = Task.Run(() => {         Thread.Sleep(1000);         Console.WriteLine('3');         return 3; }         );         Task.WaitAll(tasks);         }     } }

So in the above example, all three Tasks are executed simultaneously and it is faster.

You can use WaitAny to wait until one of the task is completed.

You may also like:

• Parallel Programming in C#
• Background worker class
• Threads in C#
• Tasks in C#
• PLINQ in C#
• Cancelling Tasks in C#
• Call a method Asynchronously in C#
• async and await keyword in C#
• Asynchronous programming in C# using Async and Await keyword
• Split Work Among Processors in C# using Parallel.For()
• Use Reader-Writer Lock in C#
• Thread Synchronization
• Threadsafe Collection

http://www.csharpstar.com/tasks-csharp/