Retrieves data from {cache_update} or empties the cache when necessary.

Two very expensive arrays computed by this module are the list of all installed modules and themes (and .info data, project associations, etc), and the current status of the site relative to the currently available releases. These two arrays are cached in the {cache_update} table and used whenever possible. The cache is cleared whenever the administrator visits the status report, available updates report, or the module or theme administration pages, since we should always recompute the most current values on any of those pages.

Note: while both of these arrays are expensive to compute (in terms of disk I/O and some fairly heavy CPU processing), neither of these is the actual data about available updates that we have to fetch over the network from updates.drupal.org. That information is stored with the 'update_available_releases' cache ID -- it needs to persist longer than 1 hour and never get invalidated just by visiting a page on the site.

Parameters

$cid: The cache ID of data to return from the cache. Valid options are 'update_project_data' and 'update_project_projects'.

Return value

The cached value of the $projects array generated by update_calculate_project_data() or update_get_projects(), or an empty array when the cache is cleared.

File

drupal-7.x/modules/update/update.compare.inc, line 779

Code required only when comparing available updates to existing data.

Code

function update_project_cache($cid) {
  $projects = array();

  // On certain paths, we should clear the cache and recompute the projects for
  // update status of the site to avoid presenting stale information.
  $q = $_GET['q'];
  $paths = array(
    'admin/modules',
    'admin/modules/update',
    'admin/appearance',
    'admin/appearance/update',
    'admin/reports',
    'admin/reports/updates',
    'admin/reports/updates/update',
    'admin/reports/status',
    'admin/reports/updates/check',
  );
  if (in_array($q, $paths)) {
    _update_cache_clear($cid);
  }
  else {
    $cache = _update_cache_get($cid);
    if (!empty($cache->data) && $cache->expire > REQUEST_TIME) {
      $projects = $cache->data;
    }
  }
  return $projects;
}