Can SCGI handle more than one request at a time?

Question

From my understanding of the SCGI specification, an SCGI server can only handle one request at a time. Is it true that SCGI servers can only handle one request at a time?

How do I work around this limitation, so that a web application served using SCGI is able to handle more than one request at a time?

I thought about starting more than one SCGI server. For example, if I start two SCGI servers listening at 127.0.0.1:8000 and 127.0.0.1:8001 respectively, I could configure the NGINX web server like this:

upstream myservers {
    server 127.0.0.1:8080;
    server 127.0.0.1:8001;
}

location / {
    include /etc/nginx/scgi_params;
    scgi_pass myservers;
}

Does this method actually allow my web application to serve more than one request at a time?

Answer 1

It is not necessary to start more than one SCGI server to handle more than one request at a time, if the SCGI server itself is able to handle more than one request at a time.

For example, an SCGI server that uses the forking or pre-forking server model will be able to handle more than one request at a time. In the forking server model, the every time the server accepts a connection, it will fork a child to handle the connection, and then go back to accepting more connections. In the pre-forking server model, the server forks several children when the server starts. All of these children block on the accept() system call until a request arrives. When a request arrives, the operating system will unblock one of these accept() to let a child handle the request. While this child is handling the request, other children are still blocking on their accept(), ready to accept other requests.