1// Copyright (c) 2012 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 BASE_SUPPORTS_USER_DATA_H_
6#define BASE_SUPPORTS_USER_DATA_H_
7
8#include <map>
9
10#include "base/base_export.h"
11#include "base/memory/linked_ptr.h"
12#include "base/memory/ref_counted.h"
13#include "base/threading/thread_checker.h"
14
15namespace base {
16
17// This is a helper for classes that want to allow users to stash random data by
18// key. At destruction all the objects will be destructed.
19class BASE_EXPORT SupportsUserData {
20 public:
21  SupportsUserData();
22
23  // Derive from this class and add your own data members to associate extra
24  // information with this object. Alternatively, add this as a public base
25  // class to any class with a virtual destructor.
26  class BASE_EXPORT Data {
27   public:
28    virtual ~Data() {}
29  };
30
31  // The user data allows the clients to associate data with this object.
32  // Multiple user data values can be stored under different keys.
33  // This object will TAKE OWNERSHIP of the given data pointer, and will
34  // delete the object if it is changed or the object is destroyed.
35  Data* GetUserData(const void* key) const;
36  void SetUserData(const void* key, Data* data);
37  void RemoveUserData(const void* key);
38
39  // SupportsUserData is not thread-safe, and on debug build will assert it is
40  // only used on one thread. Calling this method allows the caller to hand
41  // the SupportsUserData instance across threads. Use only if you are taking
42  // full control of the synchronization of that hand over.
43  void DetachUserDataThread();
44
45 protected:
46  virtual ~SupportsUserData();
47
48 private:
49  typedef std::map<const void*, linked_ptr<Data> > DataMap;
50
51  // Externally-defined data accessible by key.
52  DataMap user_data_;
53  // Guards usage of |user_data_|
54  ThreadChecker thread_checker_;
55
56  DISALLOW_COPY_AND_ASSIGN(SupportsUserData);
57};
58
59// Adapter class that releases a refcounted object when the
60// SupportsUserData::Data object is deleted.
61template <typename T>
62class UserDataAdapter : public base::SupportsUserData::Data {
63 public:
64  static T* Get(SupportsUserData* supports_user_data, const void* key) {
65    UserDataAdapter* data =
66      static_cast<UserDataAdapter*>(supports_user_data->GetUserData(key));
67    return data ? static_cast<T*>(data->object_.get()) : NULL;
68  }
69
70  UserDataAdapter(T* object) : object_(object) {}
71  T* release() { return object_.release(); }
72
73 private:
74  scoped_refptr<T> object_;
75
76  DISALLOW_COPY_AND_ASSIGN(UserDataAdapter);
77};
78
79}  // namespace base
80
81#endif  // BASE_SUPPORTS_USER_DATA_H_
82