Alex Vakulenko | 9205c77 | 2014-08-22 15:05:35 -0700 | [diff] [blame] | 1 | // Copyright 2014 The Chromium OS 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 | // Internal implementation of chromeos::Any class. |
| 6 | |
| 7 | #ifndef LIBCHROMEOS_CHROMEOS_ANY_INTERNAL_IMPL_H_ |
| 8 | #define LIBCHROMEOS_CHROMEOS_ANY_INTERNAL_IMPL_H_ |
| 9 | |
| 10 | #include <type_traits> |
| 11 | #include <typeinfo> |
| 12 | #include <utility> |
| 13 | |
| 14 | #include <base/logging.h> |
Alex Vakulenko | b381365 | 2014-08-27 08:04:22 -0700 | [diff] [blame^] | 15 | #include <chromeos/dbus/data_serialization.h> |
Alex Vakulenko | 9205c77 | 2014-08-22 15:05:35 -0700 | [diff] [blame] | 16 | |
| 17 | namespace chromeos { |
| 18 | |
| 19 | namespace internal_details { |
| 20 | |
| 21 | // An extension to std::is_convertible to allow conversion from an enum to |
| 22 | // an integral type which std::is_convertible does not indicate as supported. |
| 23 | template <typename From, typename To> |
| 24 | struct IsConvertible : public std::integral_constant<bool, |
| 25 | std::is_convertible<From, To>::value || |
| 26 | (std::is_enum<From>::value && std::is_integral<To>::value)> { |
| 27 | }; |
| 28 | // TryConvert is a helper function that does a safe compile-time conditional |
| 29 | // type cast between data types that may not be always convertible. |
| 30 | // From and To are the source and destination types. |
| 31 | // The function returns true if conversion was possible/successful. |
| 32 | template <typename From, typename To> |
| 33 | inline typename std::enable_if<IsConvertible<From, To>::value, bool>::type |
| 34 | TryConvert(const From& in, To* out) { |
| 35 | *out = static_cast<To>(in); |
| 36 | return true; |
| 37 | } |
| 38 | template <typename From, typename To> |
| 39 | inline typename std::enable_if<!IsConvertible<From, To>::value, bool>::type |
| 40 | TryConvert(const From& in, To* out) { |
| 41 | return false; |
| 42 | } |
| 43 | |
| 44 | class Buffer; // Forward declaration of data buffer container. |
| 45 | |
| 46 | // Abstract base class for contained variant data. |
| 47 | struct Data { |
| 48 | virtual ~Data() {} |
| 49 | // Returns the type information for the contained data. |
| 50 | virtual const std::type_info& GetType() const = 0; |
| 51 | // Copies the contained data to the output |buffer|. |
| 52 | virtual void CopyTo(Buffer* buffer) const = 0; |
| 53 | // Moves the contained data to the output |buffer|. |
| 54 | virtual void MoveTo(Buffer* buffer) = 0; |
| 55 | // Checks if the contained data is an integer type (not necessarily an 'int'). |
| 56 | virtual bool IsConvertibleToInteger() const = 0; |
| 57 | // Gets the contained integral value as an integer. |
| 58 | virtual intmax_t GetAsInteger() const = 0; |
Alex Vakulenko | 7c294a2 | 2014-08-23 19:31:27 -0700 | [diff] [blame] | 59 | // Writes the contained value to the D-Bus message buffer. |
| 60 | virtual bool AppendToDBusMessage(dbus::MessageWriter* writer) const = 0; |
Alex Vakulenko | 9205c77 | 2014-08-22 15:05:35 -0700 | [diff] [blame] | 61 | }; |
| 62 | |
| 63 | // Concrete implementation of variant data of type T. |
| 64 | template<typename T> |
| 65 | struct TypedData : public Data { |
| 66 | explicit TypedData(const T& value) : value_(value) {} |
| 67 | // NOLINTNEXTLINE(build/c++11) |
| 68 | explicit TypedData(T&& value) : value_(std::move(value)) {} |
| 69 | |
| 70 | const std::type_info& GetType() const override { return typeid(T); } |
| 71 | void CopyTo(Buffer* buffer) const override; |
| 72 | void MoveTo(Buffer* buffer) override; |
| 73 | bool IsConvertibleToInteger() const override { |
| 74 | return std::is_integral<T>::value || std::is_enum<T>::value; |
| 75 | } |
| 76 | intmax_t GetAsInteger() const override { |
| 77 | intmax_t int_val = 0; |
| 78 | bool converted = TryConvert(value_, &int_val); |
| 79 | CHECK(converted) << "Unable to convert value of type " << typeid(T).name() |
| 80 | << " to integer"; |
| 81 | return int_val; |
| 82 | } |
Alex Vakulenko | 7c294a2 | 2014-08-23 19:31:27 -0700 | [diff] [blame] | 83 | bool AppendToDBusMessage(dbus::MessageWriter* writer) const override { |
| 84 | return chromeos::dbus_utils::AppendValueToWriterAsVariant(writer, value_); |
| 85 | } |
Alex Vakulenko | 9205c77 | 2014-08-22 15:05:35 -0700 | [diff] [blame] | 86 | // Special methods to copy/move data of the same type |
| 87 | // without reallocating the buffer. |
| 88 | void FastAssign(const T& source) { value_ = source; } |
| 89 | // NOLINTNEXTLINE(build/c++11) |
| 90 | void FastAssign(T&& source) { value_ = std::move(source); } |
| 91 | |
| 92 | T value_; |
| 93 | }; |
| 94 | |
| 95 | // Buffer class that stores the contained variant data. |
| 96 | // To improve performance and reduce memory fragmentation, small variants |
| 97 | // are stored in pre-allocated memory buffers that are part of the Any class. |
| 98 | // If the memory requirements are larger than the set limit or the type is |
| 99 | // non-trivially copyable, then the contained class is allocated in a separate |
| 100 | // memory block and the pointer to that memory is contained within this memory |
| 101 | // buffer class. |
| 102 | class Buffer { |
| 103 | public: |
| 104 | enum StorageType { kExternal, kContained }; |
| 105 | Buffer() : external_ptr_(nullptr), storage_(kExternal) {} |
| 106 | ~Buffer() { |
| 107 | Clear(); |
| 108 | } |
| 109 | |
| 110 | Buffer(const Buffer& rhs) : Buffer() { |
| 111 | rhs.CopyTo(this); |
| 112 | } |
| 113 | // NOLINTNEXTLINE(build/c++11) |
| 114 | Buffer(Buffer&& rhs) : Buffer() { |
| 115 | rhs.MoveTo(this); |
| 116 | } |
| 117 | Buffer& operator=(const Buffer& rhs) { |
| 118 | rhs.CopyTo(this); |
| 119 | return *this; |
| 120 | } |
| 121 | // NOLINTNEXTLINE(build/c++11) |
| 122 | Buffer& operator=(Buffer&& rhs) { |
| 123 | rhs.MoveTo(this); |
| 124 | return *this; |
| 125 | } |
| 126 | |
| 127 | // Returns the underlying pointer to contained data. Uses either the pointer |
| 128 | // or the raw data depending on |storage_| type. |
| 129 | inline Data* GetDataPtr() { |
| 130 | return (storage_ == kExternal) ? |
| 131 | external_ptr_ : reinterpret_cast<Data*>(contained_buffer_); |
| 132 | } |
| 133 | inline const Data* GetDataPtr() const { |
| 134 | return (storage_ == kExternal) ? |
| 135 | external_ptr_ : reinterpret_cast<const Data*>(contained_buffer_); |
| 136 | } |
| 137 | |
| 138 | // Destroys the contained object (and frees memory if needed). |
| 139 | void Clear() { |
| 140 | Data* data = GetDataPtr(); |
| 141 | if (storage_ == kExternal) { |
| 142 | delete data; |
| 143 | } else { |
| 144 | // Call the destructor manually, since the object was constructed inline |
| 145 | // in the pre-allocated buffer. We still need to call the destructor |
| 146 | // to free any associated resources, but we can't call delete |data| here. |
| 147 | data->~Data(); |
| 148 | } |
| 149 | external_ptr_ = nullptr; |
| 150 | storage_ = kExternal; |
| 151 | } |
| 152 | |
| 153 | // Stores a value of type T. |
| 154 | template<typename T> |
| 155 | void Assign(T&& value) { // NOLINT(build/c++11) |
| 156 | using Type = typename std::decay<T>::type; |
| 157 | using DataType = TypedData<Type>; |
| 158 | Data* ptr = GetDataPtr(); |
| 159 | if (ptr && ptr->GetType() == typeid(Type)) { |
| 160 | // We assign the data to the variant container, which already |
| 161 | // has the data of the same type. Do fast copy/move with no memory |
| 162 | // reallocation. |
| 163 | DataType* typed_ptr = static_cast<DataType*>(ptr); |
| 164 | // NOLINTNEXTLINE(build/c++11) |
| 165 | typed_ptr->FastAssign(std::forward<T>(value)); |
| 166 | } else { |
| 167 | Clear(); |
| 168 | // TODO(avakulenko): [see crbug.com/379833] |
| 169 | // Unfortunately, GCC doesn't support std::is_trivially_copyable<T> yet, |
| 170 | // so using std::is_trivial instead, which is a bit more restrictive. |
| 171 | // Once GCC has support for is_trivially_copyable, update the following. |
| 172 | if (!std::is_trivial<Type>::value || |
| 173 | sizeof(DataType) > sizeof(contained_buffer_)) { |
| 174 | // If it is too big or not trivially copyable, allocate it separately. |
| 175 | // NOLINTNEXTLINE(build/c++11) |
| 176 | external_ptr_ = new DataType(std::forward<T>(value)); |
| 177 | storage_ = kExternal; |
| 178 | } else { |
| 179 | // Otherwise just use the pre-allocated buffer. |
| 180 | DataType* address = reinterpret_cast<DataType*>(contained_buffer_); |
| 181 | // Make sure we still call the copy/move constructor. |
| 182 | // Call the constructor manually by using placement 'new'. |
| 183 | // NOLINTNEXTLINE(build/c++11) |
| 184 | new (address) DataType(std::forward<T>(value)); |
| 185 | storage_ = kContained; |
| 186 | } |
| 187 | } |
| 188 | } |
| 189 | |
| 190 | // Helper methods to retrieve a reference to contained data. |
| 191 | // These assume that type checking has already been performed by Any |
| 192 | // so the type cast is valid and will succeed. |
| 193 | template<typename T> |
| 194 | const T& GetData() const { |
| 195 | using DataType = internal_details::TypedData<typename std::decay<T>::type>; |
| 196 | return static_cast<const DataType*>(GetDataPtr())->value_; |
| 197 | } |
| 198 | template<typename T> |
| 199 | T& GetData() { |
| 200 | using DataType = internal_details::TypedData<typename std::decay<T>::type>; |
| 201 | return static_cast<DataType*>(GetDataPtr())->value_; |
| 202 | } |
| 203 | |
| 204 | // Returns true if the buffer has no contained data. |
| 205 | bool IsEmpty() const { |
| 206 | return (storage_ == kExternal && external_ptr_ == nullptr); |
| 207 | } |
| 208 | |
| 209 | // Copies the data from the current buffer into the |destination|. |
| 210 | void CopyTo(Buffer* destination) const { |
| 211 | if (IsEmpty()) { |
| 212 | destination->Clear(); |
| 213 | } else { |
| 214 | GetDataPtr()->CopyTo(destination); |
| 215 | } |
| 216 | } |
| 217 | |
| 218 | // Moves the data from the current buffer into the |destination|. |
| 219 | void MoveTo(Buffer* destination) { |
| 220 | if (IsEmpty()) { |
| 221 | destination->Clear(); |
| 222 | } else { |
| 223 | if (storage_ == kExternal) { |
| 224 | destination->Clear(); |
| 225 | destination->storage_ = kExternal; |
| 226 | destination->external_ptr_ = external_ptr_; |
| 227 | external_ptr_ = nullptr; |
| 228 | } else { |
| 229 | GetDataPtr()->MoveTo(destination); |
| 230 | } |
| 231 | } |
| 232 | } |
| 233 | |
| 234 | union { |
| 235 | // |external_ptr_| is a pointer to a larger object allocated in |
| 236 | // a separate memory block. |
| 237 | Data* external_ptr_; |
| 238 | // |contained_buffer_| is a pre-allocated buffer for smaller/simple objects. |
| 239 | // Pre-allocate enough memory to store objects as big as "double". |
| 240 | unsigned char contained_buffer_[sizeof(TypedData<double>)]; |
| 241 | }; |
| 242 | // Depending on a value of |storage_|, either |external_ptr_| or |
| 243 | // |contained_buffer_| above is used to get a pointer to memory containing |
| 244 | // the variant data. |
| 245 | StorageType storage_; // Declare after the union to eliminate member padding. |
| 246 | }; |
| 247 | |
| 248 | template<typename T> |
| 249 | void TypedData<T>::CopyTo(Buffer* buffer) const { buffer->Assign(value_); } |
| 250 | template<typename T> |
| 251 | void TypedData<T>::MoveTo(Buffer* buffer) { buffer->Assign(std::move(value_)); } |
| 252 | |
| 253 | } // namespace internal_details |
| 254 | |
| 255 | } // namespace chromeos |
| 256 | |
| 257 | #endif // LIBCHROMEOS_CHROMEOS_ANY_INTERNAL_IMPL_H_ |
| 258 | |