--- a/util/channel.h 2022-01-10 03:06:56.580066258 +0800
+++ b/util/channel.h 2022-01-10 03:06:46.337071094 +0800
@@ -60,7 +60,7 @@

  private:
   std::condition_variable cv_;
-  std::mutex lock_;
+  mutable std::mutex lock_;
   std::queue<T> buffer_;
   bool eof_;
 };
diff --git a/include/rocksdb/metadata.h b/include/rocksdb/metadata.h
--- a/include/rocksdb/metadata.h
+++ b/include/rocksdb/metadata.h
@@ -15,42 +15,6 @@
 
 namespace rocksdb {
 struct ColumnFamilyMetaData;
-struct LevelMetaData;
-struct SstFileMetaData;
-
-// The metadata that describes a column family.
-struct ColumnFamilyMetaData {
-  ColumnFamilyMetaData() : size(0), file_count(0), name("") {}
-  ColumnFamilyMetaData(const std::string& _name, uint64_t _size,
-                       const std::vector<LevelMetaData>&& _levels) :
-      size(_size), name(_name), levels(_levels) {}
-
-  // The size of this column family in bytes, which is equal to the sum of
-  // the file size of its "levels".
-  uint64_t size;
-  // The number of files in this column family.
-  size_t file_count;
-  // The name of the column family.
-  std::string name;
-  // The metadata of all levels in this column family.
-  std::vector<LevelMetaData> levels;
-};
-
-// The metadata that describes a level.
-struct LevelMetaData {
-  LevelMetaData(int _level, uint64_t _size,
-                const std::vector<SstFileMetaData>&& _files) :
-      level(_level), size(_size),
-      files(_files) {}
-
-  // The level which this meta data describes.
-  const int level;
-  // The size of this level in bytes, which is equal to the sum of
-  // the file size of its "files".
-  const uint64_t size;
-  // The metadata of all sst files in this level.
-  const std::vector<SstFileMetaData> files;
-};
 
 // The metadata that describes a SST file.
 struct SstFileMetaData {
@@ -100,4 +64,38 @@ struct LiveFileMetaData : SstFileMetaData {
   std::string column_family_name;  // Name of the column family
   int level;               // Level at which this file resides.
 };
+
+// The metadata that describes a level.
+struct LevelMetaData {
+  LevelMetaData(int _level, uint64_t _size,
+                const std::vector<SstFileMetaData>&& _files) :
+      level(_level), size(_size),
+      files(_files) {}
+
+  // The level which this meta data describes.
+  const int level;
+  // The size of this level in bytes, which is equal to the sum of
+  // the file size of its "files".
+  const uint64_t size;
+  // The metadata of all sst files in this level.
+  const std::vector<SstFileMetaData> files;
+};
+
+// The metadata that describes a column family.
+struct ColumnFamilyMetaData {
+  ColumnFamilyMetaData() : size(0), file_count(0), name("") {}
+  ColumnFamilyMetaData(const std::string& _name, uint64_t _size,
+                       const std::vector<LevelMetaData>&& _levels) :
+      size(_size), name(_name), levels(_levels) {}
+
+  // The size of this column family in bytes, which is equal to the sum of
+  // the file size of its "levels".
+  uint64_t size;
+  // The number of files in this column family.
+  size_t file_count;
+  // The name of the column family.
+  std::string name;
+  // The metadata of all levels in this column family.
+  std::vector<LevelMetaData> levels;
+};
 }  // namespace rocksdb