LevelDB-course-Lab/db/memtable.h

// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.

#ifndef STORAGE_LEVELDB_DB_MEMTABLE_H_
#define STORAGE_LEVELDB_DB_MEMTABLE_H_

#include <string>
#include "include/db.h"
#include "db/dbformat.h"
#include "db/skiplist.h"
#include "util/arena.h"

namespace leveldb {

class InternalKeyComparator;
class Mutex;
class MemTableIterator;

class MemTable {
 public:
  explicit MemTable(const InternalKeyComparator& comparator);
  ~MemTable();

  // Returns an estimate of the number of bytes of data in use by this
  // data structure.
  //
  // REQUIRES: external synchronization to prevent simultaneous
  // operations on the same MemTable.
  size_t ApproximateMemoryUsage();

  // Return an iterator that yields the contents of the memtable.
  //
  // The caller must ensure that the underlying MemTable remains live
  // while the returned iterator is live.  The keys returned by this
  // iterator are internal keys encoded by AppendInternalKey in the
  // db/format.{h,cc} module.
  Iterator* NewIterator();

  // Add an entry into memtable that maps key to value at the
  // specified sequence number and with the specified type.
  // Typically value will be empty if type==kTypeDeletion.
  void Add(SequenceNumber seq, ValueType type,
           const Slice& key,
           const Slice& value);

 private:
  struct KeyComparator {
    const InternalKeyComparator comparator;
    explicit KeyComparator(const InternalKeyComparator& c) : comparator(c) { }
    int operator()(const char* a, const char* b) const;
  };
  friend class MemTableIterator;
  friend class MemTableBackwardIterator;

  typedef SkipList<const char*, KeyComparator> Table;

  KeyComparator comparator_;
  Arena arena_;
  Table table_;

  // No copying allowed
  MemTable(const MemTable&);
  void operator=(const MemTable&);
};

}

#endif  // STORAGE_LEVELDB_DB_MEMTABLE_H_