ExecutionContext of Threads

Question

What's the purpose of ExecutionContext.SuppressFlow();? In the following code what exactly gets suppressed?

I've this test code...

protected void btnSubmit_Click(object sender, EventArgs e)
{
   Thread[] th = new Thread[100];
   Thread.CurrentThread.CurrentCulture = new System.Globalization.CultureInfo("en-GB");

   AsyncFlowControl cntrl = ExecutionContext.SuppressFlow();
   for (int i = 0; i < th.Length; i++)
   {                   
      th[i] = new Thread(new ParameterizedThreadStart(ThreadMethod));
      th[i].Name = "Thread #" + (i+1).ToString();                
      th[i].Start((i+1).ToString());
   }
   ExecutionContext.RestoreFlow();

   foreach (Thread t in th)            
   {
      t.Join();
   }
   Response.Write(response);
}


String response = null;
Random rnd = new Random(1000);
private void ThreadMethod(object param)
{   
   if (param != null)
   {
      string temp = param as string;
      if (temp != null)
      {
         //To test what is the current culture I get for this thread execution
         System.Globalization.CultureInfo info = Thread.CurrentThread.CurrentCulture;
         for (int i = 0; i <= 10; i++)
         {
            Thread.Sleep(rnd.Next(2000));
            response += Thread.CurrentThread.ManagedThreadId.ToString() + ":" 
                     + Thread.CurrentThread.Name + ": " + temp + "<br/>";
         }
      }
   }
}

Answer 1

The details of ExecutionContext are very obscure, buried deep inside features like .NET Remoting and WCF. What is part of it is:

• HostExecutionContext
• IllogicalCallContext, a repository of thread specific data used by Remoting
• LogicalContext, as above
• SecurityContext
• SynchronizationContext

CultureInfo is not part of it, which can be a considerable problem if you change your main thread's default culture. There is no good way to ensure other threads run with that culture unless you explicitly write the code to switch them. That's not always practical, given that .NET is apt to run async callbacks on threadpool threads. They will be initialized to the system default culture.

Edit: this problem got fixed in .NET 4.5 with the CultureInfo.DefaultThreadCurrentCulture property.

Edit2: fixed much more thoroughly in .NET 4.6, culture now flows as expected.