By Loïc d'Anterroches,, 25th of February, 2011

Photon Life Cycle

We will try here to explain the life cycle of a request handled by Photon. This is a work in progress.

Life Cycle of the Photon Application Server

Photon is not following the traditional PHP approach of providing a clean state for each new request. Photon is providing an application server in which your application is loaded. The application server runs all the time and follow this life cycle:

  1. Startup sequence to load the configuration and register itself against Mongrel2.
  2. Wait for a request from Mongrel2.
  3. Process the request and possibly send a couple of answers or push jobs in the background tasks.
  4. Post request clean up.
  5. Depending of external signals or internal state, shutdown.
  6. Go back to step 2 to wait for another request.

A Daemon Means

Taking care of the resources. This is not something people in the PHP world are used to do as the traditional model is to trash everything after a request, but you can think of it as optimization. Just do the necessarily work and nothing more. At the end, clean after yourself.

Here are examples of what to pay attention at:

  • The global objects, if you change something at request 1, it will be available at request 2. For example, simply declare global $counter, increment it and display it in your view. You will see 1, 2, 3 etc. until you restart the server where it will go back to 1. State preservation between requests allows us to load the configuration only once, create some database connections only once, etc. This allows us to not do again and again the same things. You spare CPU cycles and this is good™.

  • Long running queries. The server is a single process, single thread daemon. That is, if your view requires 250ms to render, you are blocking other concurrent connections while rendering for 1/4 of a second. Note that this is the same for PHP as fastcgi, usually it is starting 10 children processes to cope with the concurrency. You can run hundreds of Photon servers behind Mongrel2 to serve your application, but if you run just a couple of them on a small VPS, you need to be aware of this in the case of a slashdotting of your website. Note that this approach has the great advantage of preventing your server to be overloaded, Mongrel2 will simply very efficiently pool the requests for you.