Jetpack_Sync_Settings::set_is_syncing PHP Method

    static function set_is_syncing($is_syncing)
    {
        self::$is_syncing = $is_syncing;
    }

 public function do_sync_and_set_delays($queue)
 {
     // don't sync if importing
     if (defined('WP_IMPORTING') && WP_IMPORTING) {
         return false;
     }
     // don't sync if we are throttled
     if ($this->get_next_sync_time($queue->id) > microtime(true)) {
         return false;
     }
     $start_time = microtime(true);
     Jetpack_Sync_Settings::set_is_syncing(true);
     $sync_result = $this->do_sync_for_queue($queue);
     Jetpack_Sync_Settings::set_is_syncing(false);
     $exceeded_sync_wait_threshold = microtime(true) - $start_time > (double) $this->get_sync_wait_threshold();
     if (is_wp_error($sync_result)) {
         if ('unclosed_buffer' === $sync_result->get_error_code()) {
             $this->set_next_sync_time(time() + self::QUEUE_LOCKED_SYNC_DELAY, $queue->id);
         } else {
             $this->set_next_sync_time(time() + self::WPCOM_ERROR_SYNC_DELAY, $queue->id);
         }
         $sync_result = false;
     } elseif ($exceeded_sync_wait_threshold) {
         // if we actually sent data and it took a while, wait before sending again
         $this->set_next_sync_time(time() + $this->get_sync_wait_time(), $queue->id);
     }
     return $sync_result;
 }