public void signal() {
    stateMachineLock.lock();
    try {
      stateMachineCondition.signalAll();
    } finally {
      stateMachineLock.unlock();
    }
  }
In the case of multiple copies, the minimum synchronization index is selected. In the case of
single copies, the current index is selected
iotdb-core/consensus/src/main/java/org/apache/iotdb/consensus/iot/IoTConsensusServerImpl.java