Karl Wiberg | c126937 | 2020-03-02 19:23:41 | [diff] [blame] | 1 | /* |
| 2 | * Copyright 2020 The WebRTC Project Authors. All rights reserved. |
| 3 | * |
| 4 | * Use of this source code is governed by a BSD-style license |
| 5 | * that can be found in the LICENSE file in the root of the source |
| 6 | * tree. An additional intellectual property rights grant can be found |
| 7 | * in the file PATENTS. All contributing project authors may |
| 8 | * be found in the AUTHORS file in the root of the source tree. |
| 9 | */ |
| 10 | |
| 11 | #ifndef RTC_BASE_BOUNDED_INLINE_VECTOR_IMPL_H_ |
| 12 | #define RTC_BASE_BOUNDED_INLINE_VECTOR_IMPL_H_ |
| 13 | |
| 14 | #include <stdint.h> |
| 15 | |
| 16 | #include <cstring> |
| 17 | #include <memory> |
| 18 | #include <type_traits> |
| 19 | #include <utility> |
| 20 | |
| 21 | namespace webrtc { |
| 22 | namespace bounded_inline_vector_impl { |
| 23 | |
| 24 | template <bool...> |
| 25 | struct BoolPack; |
| 26 | |
| 27 | // Tests if all its parameters (x0, x1, ..., xn) are true. The implementation |
| 28 | // checks whether (x0, x1, ..., xn, true) == (true, x0, x1, ..., xn), which is |
| 29 | // true iff true == x0 && x0 == x1 && x1 == x2 ... && xn-1 == xn && xn == true. |
| 30 | template <bool... Bs> |
| 31 | using AllTrue = std::is_same<BoolPack<Bs..., true>, BoolPack<true, Bs...>>; |
| 32 | |
| 33 | template <typename To, typename... Froms> |
| 34 | using AllConvertible = AllTrue<std::is_convertible<Froms, To>::value...>; |
| 35 | |
| 36 | // Initializes part of an uninitialized array. Unlike normal array |
| 37 | // initialization, does not zero the remaining array elements. Caller is |
| 38 | // responsible for ensuring that there is enough space in `data`. |
| 39 | template <typename T> |
| 40 | void InitializeElements(T* data) {} |
| 41 | template <typename T, typename U, typename... Us> |
| 42 | void InitializeElements(T* data, U&& element, Us&&... elements) { |
| 43 | // Placement new, because we construct a new object in uninitialized memory. |
| 44 | ::new (data) T(std::forward<U>(element)); |
| 45 | InitializeElements(data + 1, std::forward<Us>(elements)...); |
| 46 | } |
| 47 | |
Karl Wiberg | d084ea9 | 2020-03-02 20:49:20 | [diff] [blame] | 48 | // Default initializes uninitialized array elements. |
| 49 | // TODO(kwiberg): Replace with std::uninitialized_default_construct_n() (C++17). |
| 50 | template <typename T> |
| 51 | void DefaultInitializeElements(T* data, int size) { |
| 52 | for (int i = 0; i < size; ++i) { |
| 53 | // Placement new, because we construct a new object in uninitialized memory. |
| 54 | ::new (&data[i]) T; |
| 55 | } |
| 56 | } |
| 57 | |
Karl Wiberg | c126937 | 2020-03-02 19:23:41 | [diff] [blame] | 58 | // Copies from source to uninitialized destination. Caller is responsible for |
| 59 | // ensuring that there is enough space in `dst_data`. |
| 60 | template <typename T> |
| 61 | void CopyElements(const T* src_data, int src_size, T* dst_data, int* dst_size) { |
| 62 | if /*constexpr*/ (std::is_trivially_copy_constructible<T>::value) { |
| 63 | std::memcpy(dst_data, src_data, src_size * sizeof(T)); |
| 64 | } else { |
| 65 | std::uninitialized_copy_n(src_data, src_size, dst_data); |
| 66 | } |
| 67 | *dst_size = src_size; |
| 68 | } |
| 69 | |
| 70 | // Moves from source to uninitialized destination. Caller is responsible for |
| 71 | // ensuring that there is enough space in `dst_data`. |
| 72 | template <typename T> |
| 73 | void MoveElements(T* src_data, int src_size, T* dst_data, int* dst_size) { |
| 74 | if /*constexpr*/ (std::is_trivially_move_constructible<T>::value) { |
| 75 | std::memcpy(dst_data, src_data, src_size * sizeof(T)); |
| 76 | } else { |
| 77 | // TODO(kwiberg): Use std::uninitialized_move_n() instead (C++17). |
| 78 | for (int i = 0; i < src_size; ++i) { |
| 79 | // Placement new, because we create a new object in uninitialized |
| 80 | // memory. |
| 81 | ::new (&dst_data[i]) T(std::move(src_data[i])); |
| 82 | } |
| 83 | } |
| 84 | *dst_size = src_size; |
| 85 | } |
| 86 | |
| 87 | // Destroys elements, leaving them uninitialized. |
| 88 | template <typename T> |
| 89 | void DestroyElements(T* data, int size) { |
| 90 | if /*constexpr*/ (!std::is_trivially_destructible<T>::value) { |
| 91 | for (int i = 0; i < size; ++i) { |
| 92 | data[i].~T(); |
| 93 | } |
| 94 | } |
| 95 | } |
| 96 | |
| 97 | // If elements are trivial and the total capacity is at most this many bytes, |
| 98 | // copy everything instead of just the elements that are in use; this is more |
| 99 | // efficient, and makes BoundedInlineVector trivially copyable. |
| 100 | static constexpr int kSmallSize = 64; |
| 101 | |
| 102 | // Storage implementations. |
| 103 | // |
| 104 | // There are diferent Storage structs for diferent kinds of element types. The |
| 105 | // common contract is the following: |
| 106 | // |
| 107 | // * They have public `size` variables and `data` array members. |
| 108 | // |
| 109 | // * Their owner is responsible for enforcing the invariant that the first |
| 110 | // `size` elements in `data` are initialized, and the remaining elements are |
| 111 | // not initialized. |
| 112 | // |
| 113 | // * They implement default construction, construction with one or more |
| 114 | // elements, copy/move construction, copy/move assignment, and destruction; |
| 115 | // the owner must ensure that the invariant holds whenever these operations |
| 116 | // occur. |
| 117 | |
| 118 | // Storage implementation for nontrivial element types. |
| 119 | template <typename T, |
| 120 | int fixed_capacity, |
| 121 | bool is_trivial = std::is_trivial<T>::value, |
| 122 | bool is_small = (sizeof(T) * fixed_capacity <= kSmallSize)> |
| 123 | struct Storage { |
| 124 | static_assert(!std::is_trivial<T>::value, ""); |
| 125 | |
| 126 | template < |
| 127 | typename... Ts, |
| 128 | typename std::enable_if_t<AllConvertible<T, Ts...>::value>* = nullptr> |
| 129 | explicit Storage(Ts&&... elements) : size(sizeof...(Ts)) { |
| 130 | InitializeElements(data, std::forward<Ts>(elements)...); |
| 131 | } |
| 132 | |
| 133 | Storage(const Storage& other) { |
| 134 | CopyElements(other.data, other.size, data, &size); |
| 135 | } |
| 136 | |
| 137 | Storage(Storage&& other) { |
| 138 | MoveElements(other.data, other.size, data, &size); |
| 139 | } |
| 140 | |
| 141 | Storage& operator=(const Storage& other) { |
| 142 | if (this != &other) { |
| 143 | DestroyElements(data, size); |
| 144 | CopyElements(other.data, other.size, data, &size); |
| 145 | } |
| 146 | return *this; |
| 147 | } |
| 148 | |
| 149 | Storage& operator=(Storage&& other) { |
| 150 | DestroyElements(data, size); |
| 151 | size = 0; // Needed in case of self assignment. |
| 152 | MoveElements(other.data, other.size, data, &size); |
| 153 | return *this; |
| 154 | } |
| 155 | |
| 156 | ~Storage() { DestroyElements(data, size); } |
| 157 | |
| 158 | int size; |
| 159 | union { |
| 160 | // Since this array is in a union, we get to construct and destroy it |
| 161 | // manually. |
| 162 | T data[fixed_capacity]; // NOLINT(runtime/arrays) |
| 163 | }; |
| 164 | }; |
| 165 | |
| 166 | // Storage implementation for trivial element types when the capacity is small |
| 167 | // enough that we can cheaply copy everything. |
| 168 | template <typename T, int fixed_capacity> |
| 169 | struct Storage<T, fixed_capacity, /*is_trivial=*/true, /*is_small=*/true> { |
| 170 | static_assert(std::is_trivial<T>::value, ""); |
| 171 | static_assert(sizeof(T) * fixed_capacity <= kSmallSize, ""); |
| 172 | |
| 173 | template < |
| 174 | typename... Ts, |
| 175 | typename std::enable_if_t<AllConvertible<T, Ts...>::value>* = nullptr> |
| 176 | explicit Storage(Ts&&... elements) : size(sizeof...(Ts)) { |
| 177 | InitializeElements(data, std::forward<Ts>(elements)...); |
| 178 | } |
| 179 | |
| 180 | Storage(const Storage&) = default; |
| 181 | Storage& operator=(const Storage&) = default; |
| 182 | ~Storage() = default; |
| 183 | |
| 184 | int size; |
| 185 | T data[fixed_capacity]; // NOLINT(runtime/arrays) |
| 186 | }; |
| 187 | |
| 188 | // Storage implementation for trivial element types when the capacity is large |
| 189 | // enough that we want to avoid copying uninitialized elements. |
| 190 | template <typename T, int fixed_capacity> |
| 191 | struct Storage<T, fixed_capacity, /*is_trivial=*/true, /*is_small=*/false> { |
| 192 | static_assert(std::is_trivial<T>::value, ""); |
| 193 | static_assert(sizeof(T) * fixed_capacity > kSmallSize, ""); |
| 194 | |
| 195 | template < |
| 196 | typename... Ts, |
| 197 | typename std::enable_if_t<AllConvertible<T, Ts...>::value>* = nullptr> |
| 198 | explicit Storage(Ts&&... elements) : size(sizeof...(Ts)) { |
| 199 | InitializeElements(data, std::forward<Ts>(elements)...); |
| 200 | } |
| 201 | |
| 202 | Storage(const Storage& other) : size(other.size) { |
| 203 | std::memcpy(data, other.data, other.size * sizeof(T)); |
| 204 | } |
| 205 | |
| 206 | Storage& operator=(const Storage& other) { |
| 207 | if (this != &other) { |
| 208 | size = other.size; |
| 209 | std::memcpy(data, other.data, other.size * sizeof(T)); |
| 210 | } |
| 211 | return *this; |
| 212 | } |
| 213 | |
| 214 | ~Storage() = default; |
| 215 | |
| 216 | int size; |
| 217 | union { |
| 218 | T data[fixed_capacity]; // NOLINT(runtime/arrays) |
| 219 | }; |
| 220 | }; |
| 221 | |
| 222 | } // namespace bounded_inline_vector_impl |
| 223 | } // namespace webrtc |
| 224 | |
| 225 | #endif // RTC_BASE_BOUNDED_INLINE_VECTOR_IMPL_H_ |