115 lines
2.9 KiB
C++
115 lines
2.9 KiB
C++
#pragma once
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#include <array>
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#include <atomic>
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#include <cassert>
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#include <format>
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#include <iostream>
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#include <limits>
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#include <thread>
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namespace lfq {
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template <typename T, size_t Size = 256>
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class LockFreeQueue {
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static_assert(!(Size & (Size - 1)), "Size must be power of two");
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struct node {
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node() = default;
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node(size_t pos, T obj) : pos(pos), obj(obj) {}
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node(node& oth) : pos(oth.pos.load()), obj(oth.obj) {}
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node(node&& oth) : pos(oth.pos.load()), obj(std::move(oth.obj)) {}
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node& operator=(node& oth) {
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pos = oth.pos.load();
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obj = oth.obj;
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return *this;
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}
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node& operator=(node&& oth) {
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pos = oth.pos.load();
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obj = std::move(oth.obj);
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return *this;
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}
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std::atomic<size_t> pos{std::numeric_limits<size_t>::max()};
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T obj;
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};
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public:
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LockFreeQueue() : enqueue_pos(0), dequeue_pos(0) {}
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void push_back(const T& element);
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void pull_front(T& element);
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size_t apprx_available() const;
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bool is_full() const;
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bool is_empty() const;
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private:
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static constexpr size_t mask{Size - 1};
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std::atomic<size_t> enqueue_pos;
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std::atomic<size_t> dequeue_pos;
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std::array<node, Size> elements;
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};
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/**
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* @brief lfq implementation of pull operation.
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* result will be written to reference argument
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* it will block the thread until success
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*/
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template <typename T, size_t Size>
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void LockFreeQueue<T, Size>::pull_front(T& element) {
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node* n_obj;
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size_t fix_pos{0};
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bool res{false};
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while (!res) {
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while (is_empty()) {
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std::this_thread::yield();
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}
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fix_pos = dequeue_pos.load();
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n_obj = &elements[fix_pos & mask];
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if (n_obj->pos != fix_pos) {
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// someone installed the value already retry
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std::this_thread::yield();
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continue;
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}
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res = dequeue_pos.compare_exchange_weak(fix_pos, fix_pos + 1);
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}
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element = n_obj->obj;
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n_obj->pos = std::numeric_limits<size_t>::max();
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}
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/**
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* @brief lock free implementation for push back operation
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* @details trying my best to make it work :D
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*/
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template <typename T, size_t Size>
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void LockFreeQueue<T, Size>::push_back(const T& element) {
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size_t fix_pos{0};
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bool res{false};
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node obj;
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while (!res) {
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while (is_full()) {
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std::this_thread::yield();
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}
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fix_pos = enqueue_pos.load();
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obj = elements[fix_pos & mask];
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res = enqueue_pos.compare_exchange_weak(fix_pos, fix_pos + 1);
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}
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elements[fix_pos & mask] = node{fix_pos, element};
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}
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template <typename T, size_t Size>
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bool LockFreeQueue<T, Size>::is_full() const {
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assert(enqueue_pos.load() >= dequeue_pos.load());
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return enqueue_pos.load() - dequeue_pos.load() >= Size;
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}
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template <typename T, size_t Size>
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bool LockFreeQueue<T, Size>::is_empty() const {
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return enqueue_pos.load() == dequeue_pos.load();
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}
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template <typename T, size_t Size>
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size_t LockFreeQueue<T, Size>::apprx_available() const {
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assert(enqueue_pos.load() >= dequeue_pos.load());
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return enqueue_pos.load() - dequeue_pos.load();
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}
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} // namespace lfq
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