public static synchronized PipeSubtaskExecutorManager getInstance() {
    if (PipeTaskExecutorHolder.instance == null) {
      PipeTaskExecutorHolder.instance = new PipeSubtaskExecutorManager();
    }
    return PipeTaskExecutorHolder.instance;
  }
PipeTaskExecutor is responsible for executing the pipe tasks, and it is scheduled by the
PipeTaskScheduler. It is a singleton class.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/pipe/agent/task/execution/PipeSubtaskExecutorManager.java