Exception handling in asynchronous function

Exception handling in asynchronous function

In this tutorial we will try to understand how to implement try-catch block in asynchronous function in C# 5.0. I hope you have idea about asynchronous function and probably you have implemented it practically. Now we will see how to implement try-catch block in asynchronous function.

Implement traditional try-catch block

Try-catch block in asynchronous function is not like normal try-catch block in C# function. The implementation is little bit different. At first we will implement try-catch block like simple function.

Have a look on below code.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Diagnostics;
namespace Asynchronious
{
    class TestAsync
    {
        public Task LongProcess()
        {
            return Task.Run(() => {
                System.Threading.Thread.Sleep(1000);
                throw new Exception("Our own Exception");
            });
        }
        public async void CallLongTask()
        {
            await LongProcess();
        }
    }
        class Program
        {
            public static void Main(String[] args)
            {
                try
                {
                    TestAsync obj = new TestAsync();
                    obj.CallLongTask();
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                }
                Console.ReadLine();
            }
        }
}

 Here is output screen.

So, though we have wrapped all function within try-catch block but catch block is fail to catch the exception. Then, what is the solution?  We have to implement try-catch block within LongProcess() function.

Let’s see below code.

Implement try-catch within function 

Here we have implemented try-catch block within LongProcess().

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Diagnostics;
namespace Asynchronious
{
    class TestAsync
    {
        public Task LongProcess()
        {
            return Task.Run(() => {
                try
                {
                    System.Threading.Thread.Sleep(1000);
                    throw new Exception("Our own Exception");
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                }
            });
        }
        public async void CallLongTask()
        {
            await LongProcess();
        }
    }
        class Program
        {
            public static void Main(String[] args)
            {
                    TestAsync obj = new TestAsync();
                    obj.CallLongTask();
                    Console.ReadLine();
            }
        }
}

Here is sample output.

Now, we are seeing that catch block is able to catch the exception.

Conclusion :-

In this article we have learned how to implement try-catch in asynchronous function in C# 5.0. Hope you have understood the concept.