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  
15  namespace leveldb {
16  
17  class InternalKeyComparator;
18  class MemTableIterator;
19  
20  class 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_