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.

Module initialization/terminationRequest initialization/termination
Allocate/deallocate and initialize module global variablesAllocate/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:

示例 #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();
}
/* }}} */