* Ensures Drupal is bootstrapped to the specified phase.
*
* In order to bootstrap Drupal from another PHP script, you can use this code:
* @code
* define('DRUPAL_ROOT', '/path/to/drupal');
* require_once DRUPAL_ROOT . '/includes/bootstrap.inc';
* drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
* @endcode
*
* @param $phase
* A constant telling which phase to bootstrap to. When you bootstrap to a
* particular phase, all earlier phases are run automatically. Possible
* values:
* - DRUPAL_BOOTSTRAP_CONFIGURATION: Initializes configuration.
* - DRUPAL_BOOTSTRAP_PAGE_CACHE: Tries to serve a cached page.
* - DRUPAL_BOOTSTRAP_DATABASE: Initializes the database layer.
* - DRUPAL_BOOTSTRAP_VARIABLES: Initializes the variable system.
* - DRUPAL_BOOTSTRAP_SESSION: Initializes session handling.
* - DRUPAL_BOOTSTRAP_PAGE_HEADER: Sets up the page header.
* - DRUPAL_BOOTSTRAP_LANGUAGE: Finds out the language of the page.
* - DRUPAL_BOOTSTRAP_FULL: Fully loads Drupal. Validates and fixes input
* data.
* @param $new_phase
* A boolean, set to FALSE if calling drupal_bootstrap from inside a
* function called from drupal_bootstrap (recursion).
*
* @return
* The most recently completed phase.
*/
function drupal_bootstrap($phase = NULL, $new_phase = TRUE) {
// Not drupal_static(), because does not depend on any run-time information.
static $phases = array(
DRUPAL_BOOTSTRAP_CONFIGURATION,
DRUPAL_BOOTSTRAP_PAGE_CACHE,
DRUPAL_BOOTSTRAP_DATABASE,
DRUPAL_BOOTSTRAP_VARIABLES,
DRUPAL_BOOTSTRAP_SESSION,
DRUPAL_BOOTSTRAP_PAGE_HEADER,
DRUPAL_BOOTSTRAP_LANGUAGE,
DRUPAL_BOOTSTRAP_FULL,
);
// Not drupal_static(), because the only legitimate API to control this is to
// call drupal_bootstrap() with a new phase parameter.
static $final_phase;
// Not drupal_static(), because it's impossible to roll back to an earlier
// bootstrap state.
static $stored_phase = -1;
// When not recursing, store the phase name so it's not forgotten while
// recursing.
if ($new_phase) {
$final_phase = $phase;
}
if (isset($phase)) {
// Call a phase if it has not been called before and is below the requested
// phase.
while ($phases && $phase > $stored_phase && $final_phase > $stored_phase) {
$current_phase = array_shift($phases);
// This function is re-entrant. Only update the completed phase when the
// current call actually resulted in a progress in the bootstrap process.
if ($current_phase > $stored_phase) {
$stored_phase = $current_phase;
}
switch ($current_phase) {
case DRUPAL_BOOTSTRAP_CONFIGURATION:
_drupal_bootstrap_configuration();
break;
case DRUPAL_BOOTSTRAP_PAGE_CACHE:
_drupal_bootstrap_page_cache();
break;
case DRUPAL_BOOTSTRAP_DATABASE:
_drupal_bootstrap_database();
break;
case DRUPAL_BOOTSTRAP_VARIABLES:
_drupal_bootstrap_variables();
break;
case DRUPAL_BOOTSTRAP_SESSION:
require_once DRUPAL_ROOT . '/' . variable_get('session_inc', 'includes/session.inc');
drupal_session_initialize();
break;
case DRUPAL_BOOTSTRAP_PAGE_HEADER:
_drupal_bootstrap_page_header();
break;
case DRUPAL_BOOTSTRAP_LANGUAGE:
drupal_language_initialize();
break;
case DRUPAL_BOOTSTRAP_FULL:
require_once DRUPAL_ROOT . '/includes/common.inc';
_drupal_bootstrap_full();
break;
}
}
}
return $stored_phase;
}
在函数的注释里面，我们看到，Drupal的引导指令分为多个阶段，DRUPAL_BOOTSTRAP_FULL是最后一个阶段，启动Drupal引导指令的时候，可以指定具体的阶段，而不是仅仅限于最后这个阶段。
如果要在别的PHP脚本中，启动Drupal引导指令的话，可以使用下面的代码：
define('DRUPAL_ROOT', '/path/to/drupal');
require_once DRUPAL_ROOT . '/includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
我们来看函数里面的代码，首先是：
static $phases = array(
DRUPAL_BOOTSTRAP_CONFIGURATION,
DRUPAL_BOOTSTRAP_PAGE_CACHE,
DRUPAL_BOOTSTRAP_DATABASE,
DRUPAL_BOOTSTRAP_VARIABLES,
DRUPAL_BOOTSTRAP_SESSION,
DRUPAL_BOOTSTRAP_PAGE_HEADER,
DRUPAL_BOOTSTRAP_LANGUAGE,
DRUPAL_BOOTSTRAP_FULL,
);
这里面列出来了，引导指令的所有阶段，我们在think in Drupal的第一集里面，介绍过这些阶段。我们看到，这些阶段都是使用的大写字母，表示这是定义好的常量。在bootstrap.inc文件中，有这样的代码。
/**
* First bootstrap phase: initialize configuration.
*/
define('DRUPAL_BOOTSTRAP_CONFIGURATION', 0);
/**
* Second bootstrap phase: try to serve a cached page.
*/
define('DRUPAL_BOOTSTRAP_PAGE_CACHE', 1);
/**
* Third bootstrap phase: initialize database layer.
*/
define('DRUPAL_BOOTSTRAP_DATABASE', 2);
/**
* Fourth bootstrap phase: initialize the variable system.
*/
define('DRUPAL_BOOTSTRAP_VARIABLES', 3);
/**
* Fifth bootstrap phase: initialize session handling.
*/
define('DRUPAL_BOOTSTRAP_SESSION', 4);
/**
* Sixth bootstrap phase: set up the page header.
*/
define('DRUPAL_BOOTSTRAP_PAGE_HEADER', 5);
/**
* Seventh bootstrap phase: find out language of the page.
*/
define('DRUPAL_BOOTSTRAP_LANGUAGE', 6);
/**
* Final bootstrap phase: Drupal is fully loaded; validate and fix input data.
*/
define('DRUPAL_BOOTSTRAP_FULL', 7);
我们看到这些常量，从上到下，分别对应于0、1、2、3、4、5、6、7。引导指令共分为8个阶段。当我们明白了这些常量就是整数的时候，理解下面的这段代码，就很简单了。
while ($phases && $phase > $stored_phase && $final_phase > $stored_phase) {
这句话的意思使用，如果传过来的阶段为7，那么系统将会从0开始，1，2，3，4，5，6这样一直执行下去，直到执行到阶段7为止。如果传过来的阶段为3，那么将会执行0，1，2，3。就是说，从0开始，一直执行到传递过来阶段为止。引导指令是按照先后顺序，依次执行的。