function module_implements

Determines which modules are implementing a hook.

Lazy-loaded include files specified with "group" via hook_hook_info() or hook_module_implements_alter() will be automatically included by this function when necessary.


string $hook: The name of the hook (e.g. "help" or "menu").

bool $sort: By default, modules are ordered by weight and filename, settings this option to TRUE, module list will be ordered by module name.

bool $reset: For internal use only: Whether to force the stored list of hook implementations to be regenerated (such as after enabling a new module, before processing hook_enable).

Return value

An array with the names of the modules which are implementing this hook.

See also


Related topics

68 calls to module_implements()
aggregator_admin_form in modules/aggregator/
Form constructor for the aggregator system settings.
block_form_system_performance_settings_alter in modules/block/block.module
Implements hook_form_FORM_ID_alter().
boot_test_1_boot in modules/simpletest/tests/boot_test_1.module
Implements hook_boot().
DrupalDefaultEntityController::attachLoad in includes/
Attaches data to entities upon loading.
DrupalWebTestCase::tearDown in modules/simpletest/drupal_web_test_case.php
Delete created files and temporary files directory, delete the tables created by setUp(), and reset the database prefix.

... See full list

3 string references to 'module_implements'
ModuleUnitTest::testModuleImplements in modules/simpletest/tests/module.test
Test module_implements() caching.
module_implements_write_cache in includes/
Writes the hook implementation cache.
_drupal_bootstrap_full in includes/


includes/, line 727


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__);
        $drupal_static_fast['verified'] =& drupal_static(__FUNCTION__ . ':verified');
    $implementations =& $drupal_static_fast['implementations'];
    $verified =& $drupal_static_fast['verified'];
    // We maintain a persistent cache of hook implementations in addition to the
    // static cache to avoid looping through every module and every hook on each
    // request. Benchmarks show that the benefit of this caching outweighs the
    // additional database hit even when using the default database caching
    // backend and only a small number of modules are enabled. The cost of the
    // cache_get() is more or less constant and reduced further when non-database
    // caching backends are used, so there will be more significant gains when a
    // large number of modules are installed or hooks invoked, since this can
    // quickly lead to module_hook() being called several thousand times
    // per request.
    if ($reset) {
        $implementations = array();
        $verified = array();
        cache_set('module_implements', array(), 'cache_bootstrap');
        cache_clear_all('hook_info', 'cache_bootstrap');
        cache_clear_all('system_cache_tables', 'cache');
    // Fetch implementations from cache.
    // This happens on the first call to module_implements(*, *, FALSE) during a
    // request, but also when $implementations have been reset, e.g. after
    // module_enable().
    if (empty($implementations)) {
        $implementations = cache_get('module_implements', 'cache_bootstrap');
        if ($implementations === FALSE) {
            $implementations = array();
        else {
            $implementations = $implementations->data;
        // Forget all previously "verified" hooks, in case that $implementations
        // were cleared via drupal_static_reset('module_implements') instead of
        // module_implements(*, *, TRUE).
        $verified = array();
    if (!isset($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;
        // Discover implementations for this hook.
        $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') {
            // Remember the implementations before hook_module_implements_alter().
            $implementations_before = $implementations[$hook];
            drupal_alter('module_implements', $implementations[$hook], $hook);
            // Verify implementations that were added or modified.
            foreach (array_diff_assoc($implementations[$hook], $implementations_before) as $module => $group) {
                // If drupal_alter('module_implements') changed or added a $group, the
                // respective file needs to be included.
                if ($group) {
                    module_load_include('inc', $module, "{$module}.{$group}");
                // If a new implementation was added, verify that the function exists.
                if (!function_exists($module . '_' . $hook)) {
        // Implementations for this hook are now "verified".
        $verified[$hook] = TRUE;
    elseif (!isset($verified[$hook])) {
        // Implementations for this hook were in the cache, but they are not
        // "verified" yet.
        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.
                $implementations['#write_cache'] = TRUE;
        $verified[$hook] = TRUE;
    return array_keys($implementations[$hook]);

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