docs: public synchronized void shutdownImmediately() {
  
          if (!this.isShutdown) {
              final Thread runner = this.taskRunnerThread;
  
              this.isShutdown = true;
  
              if (runner != null && runner.isAlive()) {
                  runner.interrupt();
              }
  
              this.taskQueue.cancelAllTasks();
          }
      }