Using an Asynchronous Controller in ASP.NET MVC. The AsyncController class enables you to write asynchronous action methods. You can use asynchronous action methods for long-running, non-CPU bound requests. This avoids blocking the Web server from performing work while the request is being processed.

public async Task<actionresult> Index()
{
     return  View("View", await db.UserMasers.ToListAsync());
}