storage_block.h revision c7f5f8508d98d5952d42ed7648c2a8f30a4da156 
1// Copyright (c) 2006-2008 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// See net/disk_cache/disk_cache.h for the public interface.
6
7#ifndef NET_DISK_CACHE_STORAGE_BLOCK_H__
8#define NET_DISK_CACHE_STORAGE_BLOCK_H__
9
10#include "net/disk_cache/addr.h"
11#include "net/disk_cache/mapped_file.h"
12
13namespace disk_cache {
14
15class EntryImpl;
16
17// This class encapsulates common behavior of a single "block" of data that is
18// stored on a block-file. It implements the FileBlock interface, so it can be
19// serialized directly to the backing file.
20// This object provides a memory buffer for the related data, and it can be used
21// to actually share that memory with another instance of the class.
22//
23// The following example shows how to share storage with another object:
24//    StorageBlock<TypeA> a(file, address);
25//    StorageBlock<TypeB> b(file, address);
26//    a.Load();
27//    DoSomething(a.Data());
28//    b.SetData(a.Data());
29//    ModifySomething(b.Data());
30//    // Data modified on the previous call will be saved by b's destructor.
31//    b.set_modified();
32template<typename T>
33class StorageBlock : public FileBlock {
34 public:
35  StorageBlock(MappedFile* file, Addr address);
36  virtual ~StorageBlock();
37
38  // FileBlock interface.
39  virtual void* buffer() const;
40  virtual size_t size() const;
41  virtual int offset() const;
42
43  // Allows the overide of dummy values passed on the constructor.
44  bool LazyInit(MappedFile* file, Addr address);
45
46  // Sets the internal storage to share the memory provided by other instance.
47  void SetData(T* other);
48
49  // Deletes the data, even if it was modified and not saved. This object must
50  // own the memory buffer (it cannot be shared).
51  void Discard();
52
53  // Stops sharing the data with another object.
54  void StopSharingData();
55
56  // Sets the object to lazily save the in-memory data on destruction.
57  void set_modified();
58
59  // Gets a pointer to the internal storage (allocates storage if needed).
60  T* Data();
61
62  // Returns true if there is data associated with this object.
63  bool HasData() const;
64
65  // Returns true if this object owns the data buffer, false if it is shared.
66  bool own_data() const;
67
68  const Addr address() const;
69
70  // Loads and store the data.
71  bool Load();
72  bool Store();
73
74 private:
75  void AllocateData();
76  void DeleteData();
77
78  T* data_;
79  MappedFile* file_;
80  Addr address_;
81  bool modified_;
82  bool own_data_;  // Is data_ owned by this object or shared with someone else.
83  bool extended_;  // Used to store an entry of more than one block.
84
85  DISALLOW_EVIL_CONSTRUCTORS(StorageBlock);
86};
87
88typedef StorageBlock<EntryStore> CacheEntryBlock;
89typedef StorageBlock<RankingsNode> CacheRankingsBlock;
90
91}  // namespace disk_cache
92
93#endif  // NET_DISK_CACHE_STORAGE_BLOCK_H__
94