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      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 
     15 namespace leveldb {
     16 class DB;
     17 class Iterator;
     18 class Slice;
     19 class Status;
     20 class WriteBatch;
     21 }
     22 
     23 namespace sync_file_system {
     24 namespace drive_backend {
     25 
     26 class 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.
     38 class 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