Async Await Task - C# .net
Tags: asyn, await, csharp, task
Published: 2023-02-13 05:49:27

Few quiz on Async programming 

##When to use async Task in c#?
You should use async Task in C# when you want to perform a potentially long-running operation asynchronously, without blocking the execution of the calling thread. By using async and await, you can write asynchronous code that is similar in structure to synchronous code.

Here are some common scenarios where you might use async Task:

1. I/O-bound operations: For example, reading from a file or downloading a web page.

2. CPU-bound operations: For example, computing the result of a complex algorithm. However, it is important to note that async Task is not a solution for improving the performance of CPU-bound operations.

3. Long-running operations: For example, operations that might take several seconds or minutes to complete.

4. Interacting with a user interface: For example, updating the UI while a long-running operation is in progress.

By using async Task, you can ensure that your application remains responsive and does not become unresponsive or hang while a long-running operation is in progress.

Here is an example that demonstrates how to use async Task to download the content of a web page asynchronously:

```csharp
using System;
using System.Net.Http;
using System.Threading.Tasks;

namespace AsyncTaskExample
{
    class Program
    {
        static async Task Main(string[] args)
        {
            Console.WriteLine("Downloading content from the web...");

            HttpClient client = new HttpClient();
            string content = await client.GetStringAsync("https://www.example.com");

            Console.WriteLine("Content downloaded.");
            Console.WriteLine(content);

            Console.WriteLine("Press any key to exit.");
            Console.ReadKey();
        }
    }
}
```
In this example, the **_Main_** method is marked with the **_async_** keyword and returns a Task. The **_GetStringAsync_**  method is called to download the content of a web page, and the **_await_** keyword is used to wait for the task to complete. While the **_GetStringAsync_** method is running, the calling thread is free to perform other work, such as handling UI events or responding to other user input.

Once the task completes, the **_await_** keyword returns the result of the task, which is the content of the web page, and the rest of the code in the **_Main_** method continues to run.

##What is relation between async and Task?
**async** and **Task** are related concepts in C# that are used to write asynchronous code.

The **async** keyword is used to indicate that a method, lambda expression, or anonymous method can be executed asynchronously. An **async** method returns a **Task** object, which represents the asynchronous operation. The **Task** object represents the outcome of the operation, including any result that the operation returns.

The **Task** class is part of the **_System.Threading.Tasks_** namespace and is used to represent a single operation that can be executed asynchronously. A **_Task_** can represent a simple or a complex operation and can be used to encapsulate the execution of the operation, the status of the operation, and the results of the operation.

The relationship between **_async_** and **_Task_** can be summarized as follows:

- An **_async_** method returns a **_Task_** object.
- The Task object represents the outcome of the asynchronous operation.
- The async keyword and the Task class are used together to write asynchronous code that can be executed in the background without blocking the main thread.

## Can **async** await exist without **Task**?
**No, async and await cannot exist without Task.**

The async keyword is used to declare an asynchronous method, and the await keyword is used to wait for the completion of an asynchronous operation within that method. However, in order to perform an asynchronous operation, you must have something to represent it. This is where Task comes in.

Task is used to represent a single, asynchronous operation, and is returned by the async method. When you call an async method, it returns a Task that represents the asynchronous operation. You can then use the await keyword to wait for the Task to complete and retrieve the result of the operation.

In other words, async and await are used to simplify the way you write asynchronous code, but the underlying mechanism for performing asynchronous operations is the Task class. Without Task, there would be no way to represent an asynchronous operation and, as a result, the async and await keywords would not have any meaning.

##What does await keyword do?
The await keyword is used in C# to wait for the completion of an asynchronous operation represented by a Task or Task<TResult> object. The await keyword is used within an async method to specify the point at which the method should resume execution after the asynchronous operation has completed.

When an async method encounters an await keyword, it suspends execution of the method and returns control to the caller. The Task or Task<TResult> that is being awaited continues to run in the background, allowing the caller to perform other work or handle other events. When the Task completes, the method resumes execution and retrieves the result of the operation.

Here's an example to illustrate the use of await:

```csharp
using System;
using System.Threading.Tasks;

namespace AwaitExample
{
    class Program
    {
        static async Task Main(string[] args)
        {
            Console.WriteLine("Starting operation...");

            int result = await LongRunningOperationAsync();

            Console.WriteLine("Operation completed.");
            Console.WriteLine("Result: " + result);

            Console.WriteLine("Press any key to exit.");
            Console.ReadKey();
        }

        static async Task<int> LongRunningOperationAsync()
        {
            await Task.Delay(2000);
            return 42;
        }
    }
}
```
In this example, the Main method calls the LongRunningOperationAsync method, which represents a long-running operation. When the await keyword is encountered, the Main method is suspended and the LongRunningOperationAsync method continues to run in the background. When the operation completes, the method resumes execution and retrieves the result of the operation, which is 42.

##Can there be multiple await in an Async method?
Yes, there can be zero or multiple await statements in an async method. This is useful when you need to perform multiple asynchronous operations in sequence, and you want to wait for each operation to complete before proceeding to the next one.

Here's an example to illustrate this concept:

```csharp
using System;
using System.Threading.Tasks;

namespace MultipleAwaitExample
{
    class Program
    {
        static async Task Main(string[] args)
        {
            Console.WriteLine("Starting operation 1...");
            int result1 = await LongRunningOperation1Async();

            Console.WriteLine("Operation 1 completed.");
            Console.WriteLine("Result 1: " + result1);

            Console.WriteLine("Starting operation 2...");
            int result2 = await LongRunningOperation2Async();

            Console.WriteLine("Operation 2 completed.");
            Console.WriteLine("Result 2: " + result2);

            Console.WriteLine("Press any key to exit.");
            Console.ReadKey();
        }

        static async Task<int> LongRunningOperation1Async()
        {
            await Task.Delay(2000);
            return 42;
        }

        static async Task<int> LongRunningOperation2Async()
        {
            await Task.Delay(3000);
            return 123;
        }
    }
}
```

In this example, the **Main** method calls two asynchronous methods: **LongRunningOperation1Async** and **LongRunningOperation2Async**. Each method returns a **Task<int>** that represents the outcome of the operation. The **await** keyword is used to wait for each operation to complete, and the result of the operation is retrieved and stored in the **result1** and **result2** variables.