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Life cycle of an extension

A PHP extension goes through several phases during its lifetime. All of these phases are opportunities for the developer to perform various initialization, termination, or informational functions. The Zend API allows for hooks into five separate phases of an extension's existence, apart from calls by PHP functions.

Loading, unloading, and requests

As the Zend engine runs, it processes one or more "requests" from its client. In the traditional CGI implementation, this corresponds to one execution of a process. However, many other implementations, most notably the Apache module, can map many requests onto a single PHP process. A PHP extension may thus see many requests in its lifetime.

Overview

  • In the Zend API, a module is loaded into memory only once when the associated PHP process starts up. Each module receives a call to the "module initialization" function specified in its zend_module structure as it is loaded.
  • Whenever the associated PHP process starts to handle a request from its client - i.e. whenever the PHP interpreter is told to start working - each module receives a call to the "request initialization" function specified in its zend_module structure.
  • Whenever the associated PHP process is done handling a request, each module receives a call to the "request termination" function specified in its zend_module structure.
  • A given module is unloaded from memory when its associated PHP process is shut down in an orderly manner. The module receives a call to the "module termination" function specified in its zend_module structure at this time.

What to do, and when to do it

There are many tasks that might be performed at any of these four points. This table details where many common initialization and termination tasks belong.

What to do, and when to do it
Module initialization/termination Request initialization/termination
Allocate/deallocate and initialize module global variables Allocate/deallocate and initialize request-specific variables
Register/unregister class entries  
Register/unregister INI entries  
Register constants  

The phpinfo() callback

Aside from globals initialization and certain rarely-used callbacks, there is one more part of a module's lifecycle to examine: A call to phpinfo(). The output a user sees from this call, whether text or HTML or anything else, is generated by each individual extension that is loaded into the PHP interpreter at the time the call is made.

To provide for format-neutral output, the header "ext/standard/info.h" provides an array of functions to produce standardized display elements. Specifically, several functions which create the familiar tables exist:

php_info_print_table_start()
Open a table in phpinfo() output. Takes no parameters.
php_info_print_table_header()
Print a table header in phpinfo() output. Takes one parameter, the number of columns, plus the same number of char * parameters which are the texts for each column heading.
php_info_print_table_row()
Print a table row in phpinfo() output. Takes one parameter, the number of columns, plus the same number of char * parameters which are the texts for each column content.
php_info_print_table_end()
Close a table formerly opened by php_info_print_table_start(). Takes no parameters.

Using these four functions, it is possible to produce status information for nearly any combination of features in an extension. Here is the information callback from the counter extension:

Example #1 counter's PHP_MINFO function

/* {{{ PHP_MINFO(counter) */
PHP_MINFO_FUNCTION(counter)
{
    char        buf[10];

    php_info_print_table_start();
    php_info_print_table_row(2, "counter support", "enabled");
    snprintf(buf, sizeof(buf), "%ld", COUNTER_G(basic_counter_value));
    php_info_print_table_row(2, "Basic counter value", buf);
    php_info_print_table_end();
}
/* }}} */
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