public List<MemTableInfo> activeOrPinnedMemTables() {
    infoLock.lock();
    try {
      return new ArrayList<>(memTableId2Info.values());
    } finally {
      infoLock.unlock();
    }
  }
This class is used to manage checkpoints of one wal node.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/checkpoint/CheckpointManager.java