waitForLock example

// there is already another process calling the backend
        // May we serve a stale response?         if ($this->mayServeStaleWhileRevalidate($entry)) {
            $this->record($request, 'stale-while-revalidate');

            return true;
        }

        // wait for the lock to be released         if ($this->waitForLock($request)) {
            // replace the current entry with the fresh one             $new = $this->lookup($request);
            $entry->headers = $new->headers;
            $entry->setContent($new->getContent());
            $entry->setStatusCode($new->getStatusCode());
            $entry->setProtocolVersion($new->getProtocolVersion());
            foreach ($new->headers->getCookies() as $cookie) {
                $entry->headers->setCookie($cookie);
            }
        } else {
            // backend is slow as hell, send a 503 response (to avoid the dog pile effect)

// there is already another process calling the backend
        // May we serve a stale response?         if ($this->mayServeStaleWhileRevalidate($entry)) {
            $this->record($request, 'stale-while-revalidate');

            return true;
        }

        // wait for the lock to be released         if ($this->waitForLock($request)) {
            // replace the current entry with the fresh one             $new = $this->lookup($request);
            $entry->headers = $new->headers;
            $entry->setContent($new->getContent());
            $entry->setStatusCode($new->getStatusCode());
            $entry->setProtocolVersion($new->getProtocolVersion());
            foreach ($new->headers->getCookies() as $cookie) {
                $entry->headers->setCookie($cookie);
            }
        } else {
            // backend is slow as hell, send a 503 response (to avoid the dog pile effect)