@Override
  public synchronized void start() {
    if (!init) {
      initThreadPool();
      candidateCompactionTaskQueue.regsitPollLastHook(
          AbstractCompactionTask::resetCompactionCandidateStatusForAllSourceFiles);
      candidateCompactionTaskQueue.regsitPollLastHook(AbstractCompactionTask::handleTaskCleanup);
      init = true;
    }
    logger.info("Compaction task manager started.");
  }
CompactionMergeTaskPoolManager provides a ThreadPool tPro queue and run all compaction tasks.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/compaction/schedule/CompactionTaskManager.java