Get TransactionScope to work with async / await

async-await, c#, transactionscope

Solution

In .NET Framework 4.5.1, there is a set of new constructors for `TransactionScope` that take a `TransactionScopeAsyncFlowOption` parameter.

According to the MSDN, it enables transaction flow across thread continuations.

My understanding is that it is meant to allow you to write code like this:

// transaction scope
using (var scope = new TransactionScope(... ,
  TransactionScopeAsyncFlowOption.Enabled))
{
  // connection
  using (var connection = new SqlConnection(_connectionString))
  {
    // open connection asynchronously
    await connection.OpenAsync();

    using (var command = connection.CreateCommand())
    {
      command.CommandText = ...;

      // run command asynchronously
      using (var dataReader = await command.ExecuteReaderAsync())
      {
        while (dataReader.Read())
        {
          ...
        }
      }
    }
  }
  scope.Complete();
}

Problem

I'm trying to integrate `async`/`await` into our service bus. I implemented a `SingleThreadSynchronizationContext` based on this example http://blogs.msdn.com/b/pfxteam/archive/2012/01/20/10259049.aspx. And it works fine, except for one thing: `TransactionScope`. I await for stuff inside the `TransactionScope` and it breaks the `TransactionScope`. `TransactionScope` doesn't seem to play nice with `async`/`await`, certainly because it stores things in the thread using `ThreadStaticAttribute`. I get this exception: "TransactionScope nested incorrectly.". I tried to save `TransactionScope` data before queuing the task and restore it before running it, but it doesn't seem to change a thing. And `TransactionScope` code is a mess, so it's really hard to understand what's going on there. Is there a way to make it work? Is there some alternative to `TransactionScope`?

Original source