PHP Life Cycle

The PHP life cycle refers to the sequence of stages that PHP goes through from the moment a request is received until the response is sent back to the client. Here's a detailed breakdown:

1. Request Initiation

• A client (web browser, API caller, etc.) sends a request to the web server

• The web server (Apache, Nginx, etc.) recognizes the request as needing PHP processing

2. PHP Startup

• The PHP interpreter is initialized (if not already running)

• PHP loads its core extensions and configuration (php.ini)

• Memory structures are initialized

3. Module Initialization (MINIT)

• Each PHP extension executes its Module Initialization routine

• Global variables are initialized

• Resource types are registered

• This happens once when PHP starts (for SAPI modules like mod_php)

4. Request Initialization (RINIT)

• For each new request, PHP initializes the request-specific environment

• Superglobals ($_GET, $_POST, etc.) are populated

• Each extension's Request Initialization function is called

5. Script Execution

• The PHP script is compiled to opcodes (if not cached)

• The opcodes are executed

• This is where your actual PHP code runs

• Database connections, calculations, etc. happen here

6. Request Shutdown (RSHUTDOWN)

• All request-specific resources are cleaned up

• Sessions are written and closed

• Output is sent to the web server

• Each extension's Request Shutdown function is called

7. Module Shutdown (MSHUTDOWN)

• When PHP is shutting down completely (e.g., web server restart)

• All extensions clean up their global resources

• This happens once when PHP terminates

Additional Notes for Different SAPIs:

• Web Server (mod_php, PHP-FPM): MINIT/MSHUTDOWN happen once when server starts/stops; RINIT/RSHUTDOWN happen per request

• CLI: Similar to web but for a single "request" (script execution)

• Embedded: Lifecycle is controlled by the host application

Optimization Points:

• Opcode caching (OPcache) skips compilation on subsequent requests

• Persistent database connections can survive between requests

• Preloading (PHP 7.4+) allows loading classes before requests

Understanding this lifecycle helps in writing more efficient PHP applications and debugging complex issues.