Please, get in touch with the MS-PHP Core contributors and implement something similar to this:
http://php.net/manual/es/function.fastcgi-finish-request.php
Most modern frameworks rely on registering shutdown functions or similar, and IIS/FastCGI/PHP will keep the connection open (and not deliver the response until then) making them run like a snail.
The only way that FastCGI will actually end connection with the user is to send the Content-Length header, followed by content of such length. That is a nasty workaround that all these CMS do not implement, and that is not feasible to implement with modern web rendering strategies such as Big Pipe where you start streaming to the client the content of the page without knowing how much content are you actually going to send.