code: public void backpressureBarrier() throws InterruptedException, IOException {
          ClientImpl currentClient = this.getClient();
          if (currentClient == null) {
              throw new IOException("Client is unavailable for backpressureBarrier().");
          }
          currentClient.backpressureBarrier();
      }
docs: Blocks the current thread until there is no more backpressure or there are no more
  connections to the database
  
  @throws InterruptedException
  @throws IOException