queue.h

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/*
Copyright (c) 2026 MrXie1109
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
 
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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SOFTWARE.
*/
 
#pragma once
#include <atomic>
#include <memory>
#include <thread>
#include <utility>
#include <vector>
 
namespace console {
    template <class T, class Alloc = std::allocator<T>>
    class LFQueue : private Alloc {
        struct Node {
            T                   data_; 
            std::atomic<Node *> next_; 

            Node(const T &data) : data_(data), next_(nullptr) {}
            Node(T &&data) : data_(std::move(data)), next_(nullptr) {}
        };
 
        std::atomic<Node *> head_; 
        std::atomic<Node *> tail_; 

        using NodeAlloc =
            typename std::allocator_traits<Alloc>::template rebind_alloc<Node>;
        using NodeTraits = std::allocator_traits<NodeAlloc>;

        Alloc &get_alloc() { return *this; }

        Node *create_node(const T &data) {
            NodeAlloc node_alloc(get_alloc());
            Node     *node = NodeTraits::allocate(node_alloc, 1);
            NodeTraits::construct(node_alloc, node, data);
            return node;
        }

        void destroy_node(Node *node) {
            NodeAlloc node_alloc(get_alloc());
            NodeTraits::destroy(node_alloc, node);
            NodeTraits::deallocate(node_alloc, node, 1);
        }
 
    public:
        LFQueue() :
            Alloc(Alloc{}), head_(create_node(T())), tail_(head_.load()) {}

        LFQueue(const Alloc &alloc) :
            Alloc(alloc), head_(create_node(T())), tail_(head_.load()) {}

        LFQueue(Alloc &&alloc) :
            Alloc(std::move(alloc)), //
            head_(create_node(T())), tail_(head_.load()) {}

        ~LFQueue() {
            Node *head;
            Node *tail;
            while (!(head = head_.exchange(nullptr, std::memory_order_acq_rel)))
                std::this_thread::yield();
            while (!(tail = tail_.exchange(nullptr, std::memory_order_acq_rel)))
                std::this_thread::yield();
            while (head) {
                Node *next = head->next_.load(std::memory_order_relaxed);
                destroy_node(head);
                head = next;
            }
            (void)tail;
        }

        void push(const T &data) {
            Node *new_node = create_node(data);
            Node *tail;
            while (!(tail = tail_.exchange(nullptr, std::memory_order_acq_rel)))
                std::this_thread::yield();
            tail->next_.store(new_node, std::memory_order_relaxed);
            tail_.store(new_node, std::memory_order_release);
        }

        void push(T &&data) {
            Node *new_node = create_node(std::move(data));
            Node *tail;
            while (!(tail = tail_.exchange(nullptr, std::memory_order_acq_rel)))
                std::this_thread::yield();
            tail->next_.store(new_node, std::memory_order_relaxed);
            tail_.store(new_node, std::memory_order_release);
        }

        template <class Iterator>
        void push(Iterator begin, size_t count) {
            if (count == 0) return;
            Node *head = create_node(*begin), *node = head;
            try {
                for (size_t i = 1; i < count; i++) {
                    ++begin;
                    Node *next = create_node(*begin);
                    node->next_.store(next, std::memory_order_relaxed);
                    node = next;
                }
            } catch (...) {
                for (Node *p  = head; p != node;
                    /*   */ p = p->next_.load(std::memory_order_relaxed))
                    destroy_node(p);
                destroy_node(node);
                throw;
            }
            Node *tail;
            while (!(tail = tail_.exchange(nullptr, std::memory_order_acq_rel)))
                std::this_thread::yield();
            tail->next_.store(head, std::memory_order_relaxed);
            tail_.store(node, std::memory_order_release);
        }

        template <class Iterator>
        void push(Iterator begin, Iterator end) {
            push(begin, std::distance(begin, end));
        }

        bool pop(T &output) {
            Node *head;
            while (!(head = head_.exchange(nullptr, std::memory_order_acq_rel)))
                std::this_thread::yield();
            if (!head->next_) {
                head_.store(head, std::memory_order_release);
                return false;
            }
            output
                = std::move(head->next_.load(std::memory_order_relaxed)->data_);
            Node *new_head = head->next_.load(std::memory_order_relaxed);
            head_.store(new_head, std::memory_order_release);
            destroy_node(head);
            return true;
        }

        std::unique_ptr<T> pop() {
            std::unique_ptr<T> result(new T{});
            if (pop(*result)) return result;
            return nullptr;
        }

        template <class Iterator>
        size_t pop(Iterator output, size_t count) {
            Node *head, *tail;
            while (!(head = head_.exchange(nullptr, std::memory_order_acq_rel)))
                std::this_thread::yield();
            tail = head;
            for (size_t i = 0; i < count; ++i) {
                if (!tail->next_.load(std::memory_order_relaxed)) break;
                tail = tail->next_.load(std::memory_order_relaxed);
            }
            head_.store(tail, std::memory_order_release);
            size_t real_count = 0;
            while (head != tail) {
                Node *next = head->next_.load(std::memory_order_relaxed);
                *output++  = std::move(next->data_);
                destroy_node(head);
                head = next;
                ++real_count;
            }
            return real_count;
        }

        template <class Iterator>
        size_t pop(Iterator begin, Iterator end) {
            return pop(begin, std::distance(begin, end));
        }

        std::vector<T> pop(size_t count) {
            std::vector<T> result;
            result.reserve(count);
            pop(std::back_inserter(result), count);
            return result;
        }
    };

    template <class T, class Alloc = std::allocator<T>, size_t RobinTimes = 2>
    class MultiLFQueue {
        std::vector<std::unique_ptr<console::LFQueue<T, Alloc>>> queues_;
        std::atomic<size_t> round_robin_{0};
        std::atomic<size_t> nth_{0};

        size_t _index() {
            thread_local size_t idx = nth_.fetch_add(1) % queues_.size();
            return idx;
        }

        template <class OtherIterator, class IteratorTag>
        void _advance(OtherIterator &it, size_t n, IteratorTag) {
            for (size_t i = 0; i < n; ++i) ++it;
        }

        template <class RandomAccessIterator>
        void _advance(RandomAccessIterator &it,
            size_t                          n,
            std::random_access_iterator_tag) {
            it += n;
        }

        template <class Iterator>
        void _advance(Iterator &it, size_t n) {
            _advance(it,
                n,
                typename std::iterator_traits<Iterator>::iterator_category{});
        }
 
    public:
        MultiLFQueue(size_t num_queues = 1) {
            for (size_t i = 0; i < num_queues; ++i)
                queues_.emplace_back(new console::LFQueue<T, Alloc>());
        }

        template <class... Args>
        auto push(Args &&...args)
            -> decltype(queues_[_index()]->push(std::forward<Args>(args)...)) {
            return queues_[_index()]->push(std::forward<Args>(args)...);
        }

        bool pop(T &output) {
            size_t start = round_robin_.fetch_add(1, std::memory_order_relaxed);
            for (size_t i = 0; i < queues_.size() * RobinTimes; ++i) {
                size_t idx = (start + i) % queues_.size();
                if (queues_[idx]->pop(output)) return true;
            }
            return false;
        }

        std::unique_ptr<T> pop() {
            std::unique_ptr<T> result(new T{});
            if (pop(*result)) return result;
            return nullptr;
        }

        template <class Iterator>
        size_t pop(Iterator output, size_t count) {
            size_t start = round_robin_.fetch_add(1, std::memory_order_relaxed);
            size_t popped = 0;
            for (size_t i = 0; i < queues_.size() * RobinTimes; ++i) {
                size_t idx         = (start + i) % queues_.size();
                size_t popped_this = queues_[idx]->pop(output, count);
                _advance(output, popped_this);
                popped += popped_this;
                count -= popped_this;
                if (count == 0) break;
            }
            return popped;
        }

        template <class Iterator>
        size_t pop(Iterator begin, Iterator end) {
            return pop(begin, std::distance(begin, end));
        }

        std::vector<T> pop(size_t count) {
            std::vector<T> result;
            result.reserve(count);
            pop(std::back_inserter(result), count);
            return result;
        }
    };
}