HttpResponse.BeginFlush Method (AsyncCallback, Object)
Sends the currently buffered response to the client.
Assembly: System.Web (in System.Web.dll)
If the underlying HttpWorkerRequest object supports asynchronous flush operations and this method is called from an asynchronous module event or from an asynchronous handler, the flush operation is performed asynchronously. Otherwise, the flush operation is performed synchronously. Asynchronous flush is supported for IIS 6.0 and later.
Available since 4.5