Drupal 7: Hook implementations are cached in the database
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Saturday, September 10, 2011 - 11:59
Apparently drupal 7 caches its hook implementations. So when implementing a hook in D7 you need to flush cache.
The reason why this is done you can read in the module_implements function:
<?php
function module_implements($hook, $sort = FALSE, $reset = FALSE) {
// Use the advanced drupal_static() pattern, since this is called very often.
static $drupal_static_fast;
if (!isset($drupal_static_fast)) {
$drupal_static_fast['implementations'] = &drupal_static(__FUNCTION__);
}
$implementations = &$drupal_static_fast['implementations'];
// We maintain a persistent cache of hook implementations in addition to the
// static cache to avoid looping through every module and every hook on each
// request. Benchmarks show that the benefit of this caching outweighs the
// additional database hit even when using the default database caching
// backend and only a small number of modules are enabled. The cost of the
// cache_get() is more or less constant and reduced further when non-database
// caching backends are used, so there will be more significant gains when a
// large number of modules are installed or hooks invoked, since this can
// quickly lead to module_hook() being called several thousand times
// per request.
if ($reset) {
$implementations = array();
cache_set('module_implements', array(), 'cache_bootstrap');
drupal_static_reset('module_hook_info');
drupal_static_reset('drupal_alter');
cache_clear_all('hook_info', 'cache_bootstrap');
return;
}
// Fetch implementations from cache.
if (empty($implementations)) {
$implementations = cache_get('module_implements', 'cache_bootstrap');
if ($implementations === FALSE) {
$implementations = array();
}
else {
$implementations = $implementations->data;
}
}
if (!isset($implementations[$hook])) {
// The hook is not cached, so ensure that whether or not it has
// implementations, that the cache is updated at the end of the request.
$implementations['#write_cache'] = TRUE;
$hook_info = module_hook_info();
$implementations[$hook] = array();
$list = module_list(FALSE, FALSE, $sort);
foreach ($list as $module) {
$include_file = isset($hook_info[$hook]['group']) && module_load_include('inc', $module, $module . '.' . $hook_info[$hook]['group']);
// Since module_hook() may needlessly try to load the include file again,
// function_exists() is used directly here.
if (function_exists($module . '_' . $hook)) {
$implementations[$hook][$module] = $include_file ? $hook_info[$hook]['group'] : FALSE;
}
}
// Allow modules to change the weight of specific implementations but avoid
// an infinite loop.
if ($hook != 'module_implements_alter') {
drupal_alter('module_implements', $implementations[$hook], $hook);
}
}
else {
foreach ($implementations[$hook] as $module => $group) {
// If this hook implementation is stored in a lazy-loaded file, so include
// that file first.
if ($group) {
module_load_include('inc', $module, "$module.$group");
}
// It is possible that a module removed a hook implementation without the
// implementations cache being rebuilt yet, so we check whether the
// function exists on each request to avoid undefined function errors.
// Since module_hook() may needlessly try to load the include file again,
// function_exists() is used directly here.
if (!function_exists($module . '_' . $hook)) {
// Clear out the stale implementation from the cache and force a cache
// refresh to forget about no longer existing hook implementations.
unset($implementations[$hook][$module]);
$implementations['#write_cache'] = TRUE;
}
}
}
return array_keys($implementations[$hook]);
}
?>This was how it was done in drupal6. It just uses the static cache:
<?php
function module_implements($hook, $sort = FALSE, $refresh = FALSE) {
static $implementations;
if ($refresh) {
$implementations = array();
return;
}
if (!isset($implementations[$hook])) {
$implementations[$hook] = array();
$list = module_list(FALSE, TRUE, $sort);
foreach ($list as $module) {
if (module_hook($module, $hook)) {
$implementations[$hook][] = $module;
}
}
}
// The explicit cast forces a copy to be made. This is needed because
// $implementations[$hook] is only a reference to an element of
// $implementations and if there are nested foreaches (due to nested node
// API calls, for example), they would both manipulate the same array's
// references, which causes some modules' hooks not to be called.
// See also <a href="http://www.zend.com/zend/art/ref-count.php.
">http://www.zend.com/zend/art/ref-count.php.
</a> return (array) $implementations[$hook];
}
?>
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