roundrobin_pool.hpp

/*
    roundrobin pool : Add asynchrony to your apps
 
    BSD 3-Clause License
 
    Copyright (c) 2021, Siddiq Software LLC
    All rights reserved.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:
 
    1. Redistributions of source code must retain the above copyright notice, this
       list of conditions and the following disclaimer.
 
    2. Redistributions in binary form must reproduce the above copyright notice,
       this list of conditions and the following disclaimer in the documentation
       and/or other materials provided with the distribution.
 
    3. Neither the name of the copyright holder nor the names of its
       contributors may be used to endorse or promote products derived from
       this software without specific prior written permission.
 
    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
    DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
    FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
    SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
    OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
 
#pragma once
#ifndef ROUNDROBIN_POOL_HPP
#define ROUNDROBIN_POOL_HPP
 
#include <concepts>
#include <deque>
#include "simple_worker.hpp"
 
 
namespace siddiqsoft
{
    template <typename T, uint16_t N = 0>
        requires std::is_move_constructible_v<T>
    struct roundrobin_pool
    {
    public:
        roundrobin_pool(roundrobin_pool&&) = delete;
        auto operator=(roundrobin_pool&&) = delete;
        roundrobin_pool(roundrobin_pool&) = delete;
        auto operator=(roundrobin_pool&) = delete;
 

        roundrobin_pool(std::function<void(T&&)> c)
        {
            // Create as many threads as reported by the system.
            // std::deque does not relocate elements on growth, so non-movable types are safe.
            for (unsigned i = 0; i < ((N > 0) ? N : std::thread::hardware_concurrency()); i++) {
                workers.emplace_back(c);
            }
 
            // Shortcut; save the size of the array
            workersSize = workers.size();
        }

        void queue(T&& item)
        {
            // Add into the thread's internal queue using round-robin index
            // Atomic fetch_add to ensures each thread gets a unique index
            // and cast to size_t to avoid type mismatch issues
            size_t idx = nextWorkerIndex();
            workers.at(idx).queue(std::move(item));
            // Increment the queue counter with release semantics for visibility
            queueCounter.fetch_add(1, std::memory_order_release);
        }
 
#if defined(NLOHMANN_JSON_VERSION_MAJOR)
        nlohmann::json toJson() const
        {
            return {{"_typver", "siddiqsoft.asynchrony-lib.roundrobin_pool/0.10"},
                    {"workersSize", workersSize},
                    {"queueCounter", queueCounter.load(std::memory_order_acquire)}};
        }
#endif
 
#ifdef _DEBUG
    public:
        std::atomic_uint64_t queueCounter {0};
#else
    private:
        std::atomic_uint64_t queueCounter {0};
#endif
 
    private:
        std::deque<simple_worker<T>> workers {};

        uint64_t workersSize {};

        size_t nextWorkerIndex()
        {
            if (workersSize == 0) return 0;
            return static_cast<size_t>(queueCounter.load(std::memory_order_acquire) % workersSize);
        }
    };
 
#if defined(NLOHMANN_JSON_VERSION_MAJOR)
    template <typename T, uint16_t N = 0>
    static void to_json(nlohmann::json& dest, const siddiqsoft::roundrobin_pool<T, N>& src)
    {
        dest = src.toJson();
    }
#endif
 
} // namespace siddiqsoft
#endif // !ROUNDROBIN_POOL_HPP