code: public void execute() {
          State currentState = state.getAndSet(State.RUNNING);
          if (currentState == State.RUNNING) {
              throw new IllegalStateException(
                      "ExecutionChain is already running!");
          }
          executeRunnable = new ExecuteRunnable();
      }
docs: Start the chain of execution running.
  
  @throws IllegalStateException
  if the chain of execution has already been started.