leveldb_wrapper.h revision 6e8cce623b6e4fe0c9e4af605d675dd9d0338c38 
1// Copyright 2014 The Chromium 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.
4
5#ifndef CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_LEVELDB_WRAPPER_H_
6#define CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_LEVELDB_WRAPPER_H_
7
8#include <map>
9#include <string>
10
11#include "base/macros.h"
12#include "base/memory/scoped_ptr.h"
13#include "third_party/leveldatabase/src/include/leveldb/slice.h"
14
15namespace leveldb {
16class DB;
17class Iterator;
18class Slice;
19class Status;
20class WriteBatch;
21}
22
23namespace sync_file_system {
24namespace drive_backend {
25
26class SliceComparator {
27 public:
28  bool operator()(const leveldb::Slice& a, const leveldb::Slice& b) const {
29    return a.compare(b) < 0;
30  }
31};
32
33// LevelDBWrapper class wraps leveldb::DB and leveldb::WriteBatch to provide
34// transparent access to pre-commit data.
35// Put() and Delete() update data on memory, and Get() can access to those data
36// and also data on disk.  Those data on memory are written down on disk when
37// Commit() is called.
38class LevelDBWrapper {
39 private:
40  enum Operation {
41    PUT_OPERATION,
42    DELETE_OPERATION,
43  };
44  typedef std::pair<Operation, std::string> Transaction;
45  typedef std::map<std::string, Transaction, SliceComparator>
46      PendingOperationMap;
47
48 public:
49  class Iterator {
50   public:
51    explicit Iterator(LevelDBWrapper* db);
52    ~Iterator();
53
54    bool Valid();
55    void Seek(const std::string& target);
56    void SeekToFirst();
57    void SeekToLast();
58    void Next();
59    void Delete();
60    leveldb::Slice key();
61    leveldb::Slice value();
62
63   private:
64    // Advances internal iterators to be valid.
65    void AdvanceIterators();
66
67    LevelDBWrapper* db_;  // do not own
68    scoped_ptr<leveldb::Iterator> db_iterator_;
69    PendingOperationMap::iterator map_iterator_;
70
71    DISALLOW_COPY_AND_ASSIGN(Iterator);
72  };
73
74  explicit LevelDBWrapper(scoped_ptr<leveldb::DB> db);
75  ~LevelDBWrapper();
76
77  // Wrapping methods of leveldb::WriteBatch
78  void Put(const std::string& key, const std::string& value);
79  void Delete(const std::string& key);
80
81  // Wrapping methods of leveldb::DB
82  leveldb::Status Get(const std::string& key, std::string* value);
83  scoped_ptr<Iterator> NewIterator();
84
85  // Commits pending transactions to |db_| and clears cached transactions.
86  // Returns true if the commitment succeeds.
87  leveldb::Status Commit();
88
89  // Clears pending transactions.
90  void Clear();
91
92  // Returns the number of pending PUT/DELETE operations.
93  // Each counter counts operations independently, so operations on a key
94  // may be counted more than once.
95  int64 num_puts() { return num_puts_; }
96  int64 num_deletes() { return num_deletes_; }
97
98  // TODO(peria): Rename this method to GetLevelDBForTesting, after removing
99  // usages of drive_backend::MigrateDatabaseFromVxToVy() under
100  // drive_backend_v1/.
101  leveldb::DB* GetLevelDB();
102
103 private:
104  scoped_ptr<leveldb::DB> db_;
105
106  PendingOperationMap pending_;
107  int64 num_puts_;
108  int64 num_deletes_;
109
110  DISALLOW_COPY_AND_ASSIGN(LevelDBWrapper);
111};
112
113}  // namespace drive_backend
114}  // namespace sync_file_system
115
116#endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_LEVELDB_WRAPPER_H_
117