code: private static synchronized void start() throws IOException {
          if (s_tracer == null) {
              final VoltTrace tracer = new VoltTrace();
              final Thread thread = new Thread(tracer);
              thread.setDaemon(true);
              thread.start();
              s_tracer = tracer;
          }
      }
docs: Creates and starts a new tracer. If one already exists, this is a
  no-op. Synchronized to prevent multiple threads enabling it at the same
  time.