Perl is not PHP. This must not mean that you can not most often interchange things and port code between the two, however when it comes to runtime environments there are bigger differences you can not just interchange.
FCGI is on the request / protocol level already which is fully abstracted in the PHP runtime and you therefore have not as much control in PHP as you would have with Perl and use FCGI;
Therefore you can not just port that code.
Next to that fastcgi_finish_request
is totally unrelated to the Perl code. You must have confused it or thrown it in by sheer luck to give it a try. However it's not really useful in this counter example context.