 <p>The thread handling the request to the <code>Index</code> action with <code>id=101</code> of your controller should be blocked. Threads handling other requests of other sessions will not be blocked. Even other requests for the same session may not be blocked depending on <code>ReadOnly</code> session attribute of corresponding controllers <code>[SessionState(System.Web.SessionState.SessionStateBehavior.ReadOnly)]</code>.</p>