SqlConnection.OpenAsync doesn't work on .net 4.5^

Question

I have a method with a signature like this:

internal async static Task<string> Get()
{
   var SqlCon = await InitializeConnection();
   return "Foo";
}

I call this method like this:

var x = Get().Result;

Description of other method

internal async static Task<SqlConnection> InitializeConnection()
{
        SqlConnection sc;
        sc = new SqlConnection();            
        sc.ConnectionString = @"Data Source=.\MSSQL;Initial Catalog=MyDB;Integrated Security=True;Async=True";                                  
         await sc.OpenAsync();//on this line the program long waits and doesn't connect

        return sc;
    }

I checked with different correct lines of connection without use of asynchrony and everything worked. How to fix it ? Thank you.

Stephen Cleary · Accepted Answer · 2013-08-27 19:39:03Z

2

You are probably causing a deadlock by using Result. You should use await instead.

I explain this deadlock in detail on my blog. In essence, there are many contexts (such as UI or ASP.NET contexts) that only permit a single thread to execute at a time. By default, await will capture a context and resume the rest of the async method in that context. So, by (synchronously) blocking a thread in that context by calling Result, you are preventing the async method from completing.

answered Aug 27, 2013 at 19:39

Stephen Cleary

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2 Comments

John Stiks Over a year ago

I specified "await Get ()", but now as a result I receive the line "System.Threading.Tasks.Task ' 1 [System.String]".

Stephen Cleary Over a year ago

Sounds like you're using MVC 3? On ASP.NET, you must use .NET 4.5 and set your targetFramework to 4.5 in your web.config.

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