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| 1 | +#pragma once |
| 2 | + |
| 3 | +#include <condition_variable> |
| 4 | +#include <concepts> |
| 5 | +#include <cstddef> |
| 6 | +#include <functional> |
| 7 | +#include <mutex> |
| 8 | +#include <optional> |
| 9 | +#include <queue> |
| 10 | +#include <utility> |
| 11 | +#include <vector> |
| 12 | + |
| 13 | +namespace homeobject { |
| 14 | + |
| 15 | +/** |
| 16 | + * @brief Multi-Producer Multi-Consumer Priority Queue (C++20) |
| 17 | + * |
| 18 | + * Thread-safe priority queue that supports: |
| 19 | + * - Concurrent push operations from multiple producers |
| 20 | + * - Concurrent pop operations from multiple consumers |
| 21 | + * - Blocking pop when queue is empty |
| 22 | + * - Graceful shutdown via close() method |
| 23 | + * |
| 24 | + * @tparam T Element type (must be comparable) |
| 25 | + * @tparam Compare Comparison function (default: std::less for max-heap) |
| 26 | + */ |
| 27 | +template < typename T, typename Compare = std::less< T > > |
| 28 | + requires std::movable< T > && std::predicate< Compare, T, T > |
| 29 | +class MPMCPriorityQueue { |
| 30 | +public: |
| 31 | + using value_type = T; |
| 32 | + using size_type = std::size_t; |
| 33 | + using comparator_type = Compare; |
| 34 | + |
| 35 | + /** |
| 36 | + * @brief Status codes returned by pop operations |
| 37 | + */ |
| 38 | + enum class Status : uint8_t { |
| 39 | + Ok, ///< Successfully popped an element |
| 40 | + Closed ///< Queue is closed, no more elements available |
| 41 | + }; |
| 42 | + |
| 43 | + /** |
| 44 | + * @brief Result of a pop operation |
| 45 | + */ |
| 46 | + struct PopResult { |
| 47 | + Status status; |
| 48 | + std::optional< T > value; ///< Has value only if status == Ok |
| 49 | + |
| 50 | + // Convenience methods |
| 51 | + [[nodiscard]] constexpr bool is_ok() const noexcept { return status == Status::Ok; } |
| 52 | + [[nodiscard]] constexpr bool is_closed() const noexcept { return status == Status::Closed; } |
| 53 | + }; |
| 54 | + |
| 55 | + /** |
| 56 | + * @brief Construct an empty priority queue |
| 57 | + */ |
| 58 | + constexpr MPMCPriorityQueue() noexcept(std::is_nothrow_default_constructible_v< Compare >) = default; |
| 59 | + |
| 60 | + /** |
| 61 | + * @brief Destructor - automatically closes the queue |
| 62 | + */ |
| 63 | + ~MPMCPriorityQueue() { close(); } |
| 64 | + |
| 65 | + // Disable copy and move to prevent issues with condition variables |
| 66 | + MPMCPriorityQueue(const MPMCPriorityQueue&) = delete; |
| 67 | + MPMCPriorityQueue& operator=(const MPMCPriorityQueue&) = delete; |
| 68 | + MPMCPriorityQueue(MPMCPriorityQueue&&) = delete; |
| 69 | + MPMCPriorityQueue& operator=(MPMCPriorityQueue&&) = delete; |
| 70 | + |
| 71 | + /** |
| 72 | + * @brief Thread-safe push operation (copy) |
| 73 | + * |
| 74 | + * @param value Element to insert |
| 75 | + * @return true if pushed successfully, false if queue is closed |
| 76 | + */ |
| 77 | + bool push(const T& value) |
| 78 | + requires std::copy_constructible< T > |
| 79 | + { |
| 80 | + { |
| 81 | + std::scoped_lock lock(mutex_); |
| 82 | + if (closed_) [[unlikely]] { |
| 83 | + return false; // Queue is closed, cannot push |
| 84 | + } |
| 85 | + pq_.push(value); |
| 86 | + } |
| 87 | + cv_.notify_one(); // Wake one waiting consumer |
| 88 | + return true; |
| 89 | + } |
| 90 | + |
| 91 | + /** |
| 92 | + * @brief Thread-safe push operation (move) |
| 93 | + * |
| 94 | + * @param value Element to insert (will be moved) |
| 95 | + * @return true if pushed successfully, false if queue is closed |
| 96 | + */ |
| 97 | + bool push(T&& value) { |
| 98 | + { |
| 99 | + std::scoped_lock lock(mutex_); |
| 100 | + if (closed_) [[unlikely]] { return false; } |
| 101 | + pq_.push(std::move(value)); |
| 102 | + } |
| 103 | + cv_.notify_one(); |
| 104 | + return true; |
| 105 | + } |
| 106 | + |
| 107 | + /** |
| 108 | + * @brief Thread-safe pop operation |
| 109 | + * |
| 110 | + * Blocks if queue is empty and not closed. |
| 111 | + * Returns immediately if queue is closed. |
| 112 | + * |
| 113 | + * @return PopResult containing status and optional value |
| 114 | + * @note Thread-safe for multiple concurrent consumers |
| 115 | + */ |
| 116 | + [[nodiscard]] PopResult pop() { |
| 117 | + std::unique_lock lock(mutex_); |
| 118 | + |
| 119 | + // Wait until queue has elements or is closed |
| 120 | + cv_.wait(lock, [this] { return closed_ || !pq_.empty(); }); |
| 121 | + |
| 122 | + // Try to pop an element |
| 123 | + if (!pq_.empty()) { |
| 124 | + T top = std::move(const_cast< T& >(pq_.top())); |
| 125 | + pq_.pop(); |
| 126 | + return PopResult{.status = Status::Ok, .value = std::move(top)}; |
| 127 | + } |
| 128 | + |
| 129 | + // Queue is empty and closed |
| 130 | + return PopResult{.status = Status::Closed, .value = std::nullopt}; |
| 131 | + } |
| 132 | + |
| 133 | + /** |
| 134 | + * @brief Close the queue |
| 135 | + * |
| 136 | + * After calling close(): |
| 137 | + * - All blocked pop() calls will wake up |
| 138 | + * - Existing elements can still be popped |
| 139 | + * - New push() calls will be ignored |
| 140 | + * - pop() returns Status::Closed when queue becomes empty |
| 141 | + * |
| 142 | + * @note Thread-safe and idempotent |
| 143 | + */ |
| 144 | + void close() noexcept { |
| 145 | + { |
| 146 | + std::scoped_lock lock(mutex_); |
| 147 | + closed_ = true; |
| 148 | + } |
| 149 | + cv_.notify_all(); // Wake all waiting consumers |
| 150 | + } |
| 151 | + |
| 152 | + /** |
| 153 | + * @brief Get current number of elements |
| 154 | + * |
| 155 | + * @return Number of elements in the queue |
| 156 | + * @note Thread-safe |
| 157 | + */ |
| 158 | + [[nodiscard]] size_type size() const { |
| 159 | + std::scoped_lock lock(mutex_); |
| 160 | + return pq_.size(); |
| 161 | + } |
| 162 | + |
| 163 | + /** |
| 164 | + * @brief Check if queue is empty |
| 165 | + * |
| 166 | + * @return true if queue has no elements |
| 167 | + * @note Thread-safe |
| 168 | + */ |
| 169 | + [[nodiscard]] bool empty() const { |
| 170 | + std::scoped_lock lock(mutex_); |
| 171 | + return pq_.empty(); |
| 172 | + } |
| 173 | + |
| 174 | + /** |
| 175 | + * @brief Check if queue is closed |
| 176 | + * |
| 177 | + * @return true if close() has been called |
| 178 | + * @note Thread-safe |
| 179 | + */ |
| 180 | + [[nodiscard]] bool is_closed() const { |
| 181 | + std::scoped_lock lock(mutex_); |
| 182 | + return closed_; |
| 183 | + } |
| 184 | + |
| 185 | +private: |
| 186 | + mutable std::mutex mutex_; |
| 187 | + std::condition_variable cv_; |
| 188 | + bool closed_{false}; |
| 189 | + std::priority_queue< T, std::vector< T >, Compare > pq_; |
| 190 | +}; |
| 191 | + |
| 192 | +} // namespace homeobject |
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