This scenario can be really problematic for large number of concurrent requests. If the server is busy processing all these synchronous requests, the ‘Server Busy’ status code is send to the client.
To handle this effectively, in MVC, Asynchronous controllers can be used to process requests. The mechanism used by the asynchronous controller is that, the thread on which the request is put is freed and allocated back to the ThreadPool. When the response is ready, it is allocated on the other thread.
Async Controllers before .NET 4.5The question arises here is that when to make use of the Asynchronous Controller, some considerations are as follows:
- A Long running operation which is threat to the application performance because of thread blocking.
- Operations making large transactions which utilize Network and IO resources.
- Making calls to external WCF services
- Async Action method e.g. (IndexAsync), this method starts asynchronous process and returns void.
- Completed Action method e.g. (IndexCompleted), this is called when the asynchronous operation is completed and returns ActionResult.
public class EmployeeController : AsyncController
public void IndexAsync()
MyRef.ServiceClient Proxy = new MyRef.ServiceClient();
//When Complete, result will be received in the o/p Parameter
Proxy.GetEmployeesCompleted += (sender, evt) =>
AsyncManager.Parameters["Employees"] = evt.Result;
AsyncManager.OutstandingOperations.Decrement(); //Close Polling
Proxy.GetEmployeesAsync(); // Async method Call Initiated
public ActionResult IndexCompleted(IEnumerable<Employee> Employees)
ViewData["Employees"] = Employees;
This implementation is a bit complex and it makes use of AsyncManager.OutstandingOperations, this is incremented before the operation is being started and Decremented when it is completed. Here the problem is as a developer, a lot of boilerplate has to be written. So how can we minimize it?
Async Controllers in .NET 4.5In .NET Framework 4.5 we have two new keywords ‘async’ and ‘await’. So the above code can be easily reduced.
To implement the new Asynchronous Controller programming, I have created a WCF service which contains an ADO.NET EF. This service contains a method which return Employee’ List, the implementation is as below:
The DB Script:
CREATE TABLE [dbo].[EmployeeInfo](
[EmpNo] [int] IDENTITY(1,1) NOT NULL,
[EmpName] [varchar](50) NOT NULL,
[Salary] [decimal](18, 0) NOT NULL,
[DeptName] [varchar](50) NOT NULL,
[Designation] [varchar](50) NOT NULL,
CONSTRAINT [PK_EmployeeInfo] PRIMARY KEY CLUSTERED
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
SET ANSI_PADDING OFF
The WCF Service
public interface IService
public class Service : IService
objContext = new CompanyEntities();
public List<EmployeeInfo> GetEmployees()
var Emps = objContext.EmployeeInfoes.ToList();
Consume the Service in MVC 4 project, make sure that you use target framework as .NET 4.5. (You can also use svcutil tool to generate the proxy.)
Add the new controller in the MVC project and add the following code:
public class EmployeeInfoController : AsyncController
Proxy = new ServiceClient();
public async Task<ActionResult> Index()
var Emps = await Proxy.GetEmployeesAsync();
When we compare the above code of Index method with the code for Async operations explained earlier in the article, it’s really simple and maintainable. The ‘async’ and ‘await’ keywords takes care of the required asynchronous operation.
ConclusionThe async and await keywords help us write concise code when developing Asynchronous Controllers in ASP.NET MVC thus helping in building applications that can accept more requests than their synchronous counterparts.
Will you give this article a +1 ? Thanks in advance