1 /* 2 * Copyright (C) 2016 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef CHRE_UTIL_ARRAY_QUEUE_H_ 18 #define CHRE_UTIL_ARRAY_QUEUE_H_ 19 20 #include <cstddef> 21 #include <iterator> 22 #include <type_traits> 23 24 #include "chre/util/non_copyable.h" 25 26 namespace chre { 27 28 /** 29 * A fixed-size FIFO queue for storing elements. When the FIFO is full, new 30 * element will not be able to be pushed in. 31 */ 32 template<typename ElementType, size_t kCapacity> 33 class ArrayQueue : public NonCopyable { 34 public: 35 /** 36 * Calls the destructor of all the elements in the array queue. 37 */ 38 ~ArrayQueue(); 39 40 /** 41 * Determines whether the array queue is empty or not. 42 * 43 * @return true if the array queue is empty. 44 */ 45 bool empty() const; 46 47 /** 48 * @return true if the array queue is full. 49 */ 50 bool full() const; 51 52 /** 53 * Obtains the number of elements currently stored in the array queue. 54 * 55 * @return The number of elements currently stored in the array queue. 56 */ 57 size_t size() const; 58 59 /** 60 * Obtains the front element of the array queue. It is illegal to access the 61 * front element when the array queue is empty. The user of the API must check 62 * the size() or empty() function prior to accessing the front element to 63 * ensure that they will not read out of bounds. 64 * 65 * @return The front element. 66 */ 67 ElementType& front(); 68 const ElementType& front() const; 69 70 /** 71 * Obtains the last element in the queue. Illegal to call when empty() is 72 * true. 73 * 74 * @return The last element in the queue. 75 */ 76 ElementType& back(); 77 const ElementType& back() const; 78 79 /** 80 * Obtains an element of the array queue given an index. It is illegal to 81 * index this array queue out of bounds and the user of the API must check the 82 * size() function prior to indexing this array queue to ensure that they will 83 * not read out of bounds. 84 * 85 * @param index Requested index in range [0,size()-1] 86 * @return The element. 87 */ 88 ElementType& operator[](size_t index); 89 90 /** 91 * Obtains an element of the array queue given an index. It is illegal to 92 * index this array queue out of bounds and the user of the API must check the 93 * size() function prior to indexing this array queue to ensure that they will 94 * not read out of bounds. 95 * 96 * @param index Requested index in range [0,size()-1] 97 * @return The element. 98 */ 99 const ElementType& operator[](size_t index) const; 100 101 /** 102 * Pushes an element onto the back of the array queue via copy or move 103 * construction. It returns false if the array queue is full already and there 104 * is no room for the elements. All iterators and references are unaffected. 105 * 106 * @param element The element to push onto the array queue. 107 * @return true if the element is pushed successfully. 108 */ 109 bool push(const ElementType& element); 110 bool push(ElementType&& element); 111 112 /** 113 * Removes the front element from the array queue if the array queue is not 114 * empty. Only iterators and references to the front of the queue are 115 * invalidated. 116 */ 117 void pop(); 118 119 /** 120 * Removes the back element from the array queue if the array queue is not 121 * empty. Only iterators and references to the back of the queue are 122 * invalidated. 123 */ 124 void pop_back(); 125 126 /** 127 * Removes an element from the array queue given an index. It returns false if 128 * the array queue contains fewer items than the index. All iterators and 129 * references to elements before the removed one are unaffected. Iterators 130 * and references to the removed element or any elements after it are 131 * invalidated. 132 * 133 * @param index Requested index in range [0,size()-1] 134 * @return true if the indexed element has been removed successfully. 135 */ 136 bool remove(size_t index); 137 138 /** 139 * Constructs an element onto the back of the array queue. All iterators and 140 * references are unaffected. 141 * 142 * @param The arguments to the constructor 143 * @return true if the element is constructed successfully. 144 */ 145 template<typename... Args> 146 bool emplace(Args&&... args); 147 148 /** 149 * A template class that implements a forward iterator for the array queue. 150 */ 151 template<typename ValueType> 152 class ArrayQueueIterator { 153 public: 154 typedef ValueType value_type; 155 typedef ValueType& reference; 156 typedef ValueType* pointer; 157 typedef std::ptrdiff_t difference_type; 158 typedef std::forward_iterator_tag iterator_category; 159 160 ArrayQueueIterator() = default; ArrayQueueIterator(ValueType * pointer,ValueType * base,size_t tail)161 ArrayQueueIterator( 162 ValueType *pointer, ValueType *base, size_t tail) 163 : mPointer(pointer), mBase(base), mTail(tail) {} 164 165 bool operator==(const ArrayQueueIterator& right) const { 166 return (mPointer == right.mPointer); 167 } 168 169 bool operator!=(const ArrayQueueIterator& right) const { 170 return (mPointer != right.mPointer); 171 } 172 173 ValueType& operator*() { 174 return *mPointer; 175 } 176 177 ValueType *operator->() { 178 return mPointer; 179 } 180 181 ArrayQueueIterator& operator++() { 182 if (mPointer == (mBase + mTail)) { 183 // Jump to end() if at tail 184 mPointer = mBase + kCapacity; 185 } else if (mPointer == (mBase + kCapacity - 1)) { 186 // Wrap around in the memory 187 mPointer = mBase; 188 } else { 189 mPointer++; 190 } 191 return *this; 192 } 193 194 ArrayQueueIterator operator++(int) { 195 ArrayQueueIterator it(*this); 196 operator++(); 197 return it; 198 } 199 200 private: 201 //! Pointer of the iterator. 202 ValueType *mPointer; 203 204 //! The memory base address of this container. 205 ValueType *mBase; 206 207 //! The tail offset relative to the memory base address. 208 size_t mTail; 209 }; 210 211 /** 212 * Forward iterator that points to some element in the container. 213 */ 214 typedef ArrayQueueIterator<ElementType> iterator; 215 typedef ArrayQueueIterator<const ElementType> const_iterator; 216 217 /** 218 * @return A forward iterator to the beginning. 219 */ 220 typename ArrayQueue<ElementType, kCapacity>::iterator begin(); 221 typename ArrayQueue<ElementType, kCapacity>::const_iterator begin() const; 222 typename ArrayQueue<ElementType, kCapacity>::const_iterator cbegin() const; 223 224 /** 225 * @return A forward iterator to the end. 226 */ 227 typename ArrayQueue<ElementType, kCapacity>::iterator end(); 228 typename ArrayQueue<ElementType, kCapacity>::const_iterator end() const; 229 typename ArrayQueue<ElementType, kCapacity>::const_iterator cend() const; 230 231 private: 232 /** 233 * Storage for array queue elements. To avoid static initialization of 234 * members, std::aligned_storage is used. 235 */ 236 typename std::aligned_storage<sizeof(ElementType), 237 alignof(ElementType)>::type mData[kCapacity]; 238 239 /* 240 * Initialize mTail to be (kCapacity-1). When an element is pushed in, 241 * mHead and mTail will align. Also, this is consistent with 242 * mSize = (mTail - mHead)%kCapacity + 1 for mSize > 0. 243 */ 244 //! Index of the front element 245 size_t mHead = 0; 246 247 //! Index of the back element 248 size_t mTail = kCapacity - 1; 249 250 //! Number of elements in the array queue 251 size_t mSize = 0; 252 253 /** 254 * Obtains a pointer to the underlying storage for the vector. 255 * 256 * @return A pointer to the storage used for elements in this vector. 257 */ 258 ElementType *data(); 259 260 /** 261 * Obtains a pointer to the underlying storage for the vector. 262 * 263 * @return A pointer to the storage used for elements in this vector. 264 */ 265 const ElementType *data() const; 266 267 /** 268 * Converts relative index with respect to mHead to absolute index in the 269 * storage array. 270 * 271 * @param index Relative index in range [0,size()-1] 272 * @return The index of the storage array in range [0,kCapacity-1] 273 */ 274 size_t relativeIndexToAbsolute(size_t index) const; 275 276 /* 277 * Pulls mHead to the next element in the array queue and decrements mSize 278 * accordingly. It is illegal to call this function on an empty array queue. 279 */ 280 void pullHead(); 281 282 /* 283 * Pulls mTail to the previous element in the array queue and decrements mSize 284 * accordingly. It is illegal to call this function on an empty array queue. 285 */ 286 void pullTail(); 287 288 /* 289 * Pushes mTail to the next available storage space and increments mSize 290 * accordingly. 291 * 292 * @return true if the array queue is not full. 293 */ 294 bool pushTail(); 295 }; 296 297 } // namespace chre 298 299 #include "chre/util/array_queue_impl.h" 300 301 #endif // CHRE_UTIL_ARRAY_QUEUE_H_ 302