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. 4 5 #ifndef BASE_SUPPORTS_USER_DATA_H_ 6 #define BASE_SUPPORTS_USER_DATA_H_ 7 8 #include <map> 9 #include <memory> 10 11 #include "base/base_export.h" 12 #include "base/memory/scoped_refptr.h" 13 #include "base/sequence_checker.h" 14 15 namespace 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. 19 class BASE_EXPORT SupportsUserData { 20 public: 21 SupportsUserData(); 22 SupportsUserData(SupportsUserData&&); 23 SupportsUserData& operator=(SupportsUserData&&); 24 SupportsUserData(const SupportsUserData&) = delete; 25 SupportsUserData& operator=(const SupportsUserData&) = delete; 26 27 // Derive from this class and add your own data members to associate extra 28 // information with this object. Alternatively, add this as a public base 29 // class to any class with a virtual destructor. 30 class BASE_EXPORT Data { 31 public: 32 virtual ~Data() = default; 33 34 // Returns a copy of |this|; null if copy is not supported. 35 virtual std::unique_ptr<Data> Clone(); 36 }; 37 38 // The user data allows the clients to associate data with this object. 39 // |key| must not be null--that value is too vulnerable for collision. 40 // NOTE: SetUserData() with an empty unique_ptr behaves the same as 41 // RemoveUserData(). 42 Data* GetUserData(const void* key) const; 43 [[nodiscard]] std::unique_ptr<Data> TakeUserData(const void* key); 44 void SetUserData(const void* key, std::unique_ptr<Data> data); 45 void RemoveUserData(const void* key); 46 47 // Adds all data from |other|, that is clonable, to |this|. That is, this 48 // iterates over the data in |other|, and any data that returns non-null from 49 // Clone() is added to |this|. 50 void CloneDataFrom(const SupportsUserData& other); 51 52 // SupportsUserData is not thread-safe, and on debug build will assert it is 53 // only used on one execution sequence. Calling this method allows the caller 54 // to hand the SupportsUserData instance across execution sequences. Use only 55 // if you are taking full control of the synchronization of that hand over. 56 void DetachFromSequence(); 57 58 protected: 59 virtual ~SupportsUserData(); 60 61 // Clear all user data from this object. This can be used if the subclass 62 // needs to provide reset functionality. 63 void ClearAllUserData(); 64 65 private: 66 struct Impl; 67 std::unique_ptr<Impl> impl_; 68 bool in_clear_ = false; 69 // Guards usage of |impl_| 70 SEQUENCE_CHECKER(sequence_checker_); 71 }; 72 73 // Adapter class that releases a refcounted object when the 74 // SupportsUserData::Data object is deleted. 75 template <typename T> 76 class UserDataAdapter : public SupportsUserData::Data { 77 public: Get(const SupportsUserData * supports_user_data,const void * key)78 static T* Get(const SupportsUserData* supports_user_data, const void* key) { 79 UserDataAdapter* data = 80 static_cast<UserDataAdapter*>(supports_user_data->GetUserData(key)); 81 return data ? static_cast<T*>(data->object_.get()) : nullptr; 82 } 83 UserDataAdapter(T * object)84 explicit UserDataAdapter(T* object) : object_(object) {} 85 UserDataAdapter(const UserDataAdapter&) = delete; 86 UserDataAdapter& operator=(const UserDataAdapter&) = delete; 87 ~UserDataAdapter() override = default; 88 release()89 T* release() { return object_.release(); } 90 91 private: 92 scoped_refptr<T> const object_; 93 }; 94 95 } // namespace base 96 97 #endif // BASE_SUPPORTS_USER_DATA_H_ 98