public function getAllInstances()
    {
        $cacheId = CacheId::pluginAware('ProfileSummaries');
        $cache   = Cache::getTransientCache();

        if (!$cache->contains($cacheId)) {
            $instances = [];

            /**
             * Triggered to add new live profile summaries.
             *
             * **Example**
             *
             *     public function addProfileSummary(&$profileSummaries)
             *     {
             *         $profileSummaries[] = new MyCustomProfileSummary();
             *     }
             *
             * @param ProfileSummaryAbstract[] $profileSummaries An array of profile summaries
             */
            Piwik::postEvent('Live.addProfileSummaries', array(&$instances));

            foreach ($this->getAllProfileSummaryClasses() as $className) {
                $instances[] = new $className();
            }

            /**
             * Triggered to filter / restrict profile summaries.
             *
             * **Example**
             *
             *     public function filterProfileSummary(&$profileSummaries)
             *     {
             *         foreach ($profileSummaries as $index => $profileSummary) {
             *              if ($profileSummary->getId() === 'myid') {}
             *                  unset($profileSummaries[$index]); // remove all summaries having this ID
             *              }
             *         }
             *     }
             *
             * @param ProfileSummaryAbstract[] $profileSummaries An array of profile summaries
             */
            Piwik::postEvent('Live.filterProfileSummaries', array(&$instances));

            $cache->save($cacheId, $instances);
        }

        return $cache->fetch($cacheId);
    }