1 // Copyright 2012 The Chromium Authors
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #ifndef BASE_SUPPORTS_USER_DATA_H_
6 #define BASE_SUPPORTS_USER_DATA_H_
11 #include "base/base_export.h"
12 #include "base/memory/scoped_refptr.h"
13 #include "base/sequence_checker.h"
14 #include "third_party/abseil-cpp/absl/container/flat_hash_map.h"
18 // This is a helper for classes that want to allow users to stash random data by
19 // key. At destruction all the objects will be destructed.
20 class BASE_EXPORT SupportsUserData {
23 SupportsUserData(SupportsUserData&&);
24 SupportsUserData& operator=(SupportsUserData&&);
25 SupportsUserData(const SupportsUserData&) = delete;
26 SupportsUserData& operator=(const SupportsUserData&) = delete;
28 // Derive from this class and add your own data members to associate extra
29 // information with this object. Alternatively, add this as a public base
30 // class to any class with a virtual destructor.
31 class BASE_EXPORT Data {
33 virtual ~Data() = default;
35 // Returns a copy of |this|; null if copy is not supported.
36 virtual std::unique_ptr<Data> Clone();
39 // The user data allows the clients to associate data with this object.
40 // |key| must not be null--that value is too vulnerable for collision.
41 // NOTE: SetUserData() with an empty unique_ptr behaves the same as
43 Data* GetUserData(const void* key) const;
44 [[nodiscard]] std::unique_ptr<Data> TakeUserData(const void* key);
45 void SetUserData(const void* key, std::unique_ptr<Data> data);
46 void RemoveUserData(const void* key);
48 // Adds all data from |other|, that is clonable, to |this|. That is, this
49 // iterates over the data in |other|, and any data that returns non-null from
50 // Clone() is added to |this|.
51 void CloneDataFrom(const SupportsUserData& other);
53 // SupportsUserData is not thread-safe, and on debug build will assert it is
54 // only used on one execution sequence. Calling this method allows the caller
55 // to hand the SupportsUserData instance across execution sequences. Use only
56 // if you are taking full control of the synchronization of that hand over.
57 void DetachFromSequence();
60 virtual ~SupportsUserData();
62 // Clear all user data from this object. This can be used if the subclass
63 // needs to provide reset functionality.
64 void ClearAllUserData();
67 // Externally-defined data accessible by key.
68 absl::flat_hash_map<const void*, std::unique_ptr<Data>> user_data_;
69 bool in_destructor_ = false;
70 // Guards usage of |user_data_|
71 SEQUENCE_CHECKER(sequence_checker_);
74 // Adapter class that releases a refcounted object when the
75 // SupportsUserData::Data object is deleted.
77 class UserDataAdapter : public SupportsUserData::Data {
79 static T* Get(const SupportsUserData* supports_user_data, const void* key) {
80 UserDataAdapter* data =
81 static_cast<UserDataAdapter*>(supports_user_data->GetUserData(key));
82 return data ? static_cast<T*>(data->object_.get()) : nullptr;
85 explicit UserDataAdapter(T* object) : object_(object) {}
86 UserDataAdapter(const UserDataAdapter&) = delete;
87 UserDataAdapter& operator=(const UserDataAdapter&) = delete;
88 ~UserDataAdapter() override = default;
90 T* release() { return object_.release(); }
93 scoped_refptr<T> const object_;
98 #endif // BASE_SUPPORTS_USER_DATA_H_