Inside Bitcoin

1// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file. See the AUTHORS file for names of contributors.
4
5#ifndef STORAGE_LEVELDB_DB_MEMTABLE_H_
6#define STORAGE_LEVELDB_DB_MEMTABLE_H_
7
8#include <string>
9
10#include "db/dbformat.h"
11#include "db/skiplist.h"
12#include "leveldb/db.h"
13#include "util/arena.h"
14
15namespace leveldb {
16
17class InternalKeyComparator;
18class MemTableIterator;
19
20class MemTable {
21 public:
22  // MemTables are reference counted.  The initial reference count
23  // is zero and the caller must call Ref() at least once.
24  explicit MemTable(const InternalKeyComparator& comparator);
25
26  MemTable(const MemTable&) = delete;
27  MemTable& operator=(const MemTable&) = delete;
28
29  // Increase reference count.
30  void Ref() { ++refs_; }
31
32  // Drop reference count.  Delete if no more references exist.
33  void Unref() {
34    --refs_;
35    assert(refs_ >= 0);
36    if (refs_ <= 0) {
37      delete this;
38    }
39  }
40
41  // Returns an estimate of the number of bytes of data in use by this
42  // data structure. It is safe to call when MemTable is being modified.
43  size_t ApproximateMemoryUsage();
44
45  // Return an iterator that yields the contents of the memtable.
46  //
47  // The caller must ensure that the underlying MemTable remains live
48  // while the returned iterator is live.  The keys returned by this
49  // iterator are internal keys encoded by AppendInternalKey in the
50  // db/format.{h,cc} module.
51  Iterator* NewIterator();
52
53  // Add an entry into memtable that maps key to value at the
54  // specified sequence number and with the specified type.
55  // Typically value will be empty if type==kTypeDeletion.
56  void Add(SequenceNumber seq, ValueType type, const Slice& key,
57           const Slice& value);
58
59  // If memtable contains a value for key, store it in *value and return true.
60  // If memtable contains a deletion for key, store a NotFound() error
61  // in *status and return true.
62  // Else, return false.
63  bool Get(const LookupKey& key, std::string* value, Status* s);
64
65 private:
66  friend class MemTableIterator;
67  friend class MemTableBackwardIterator;
68
69  struct KeyComparator {
70    const InternalKeyComparator comparator;
71    explicit KeyComparator(const InternalKeyComparator& c) : comparator(c) {}
72    int operator()(const char* a, const char* b) const;
73  };
74
75  typedef SkipList<const char*, KeyComparator> Table;
76
77  ~MemTable();  // Private since only Unref() should be used to delete it
78
79  KeyComparator comparator_;
80  int refs_;
81  Arena arena_;
82  Table table_;
83};
84
85}  // namespace leveldb
86
87#endif  // STORAGE_LEVELDB_DB_MEMTABLE_H_
88