C# - Access Session Value During Concurrent Requests

in one request i am updating session variable. in the other request, i am trying to access that session value, but it was blocked until the first request finish. I am using C# with ASP.NET 2.0 UPDATE: My page code looks like this.

while(int progress = DoWork() && progress <= 100 ){
Session["Progress"] = progress;
}

and my handler just return Session value.

context.Response.Write(Session["progress"].toString());
context.Response.End();