pool.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
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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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
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*/
 
#pragma once
#include <atomic>
#include <condition_variable>
#include <functional>
#include <future>
#include <memory>
#include <mutex>
#include <queue>
#include <thread>
#include <type_traits>
#include <utility>
#include <vector>
 
#include "../core/csexc.h"
 
namespace console {
    class ThreadPool {
    public:
        enum class launch : bool {
            abort, 
            close  
        };
 
    private:
        struct TaskBase {
            virtual ~TaskBase()    = default;
            virtual void execute() = 0;
        };

        template <class T>
        struct Task : public TaskBase {
            std::packaged_task<T()> task;
            Task(std::packaged_task<T()> &&t) : task(std::move(t)) {}
            void execute() override { task(); }
        };
 
        std::vector<std::thread>              workers; 
        std::queue<std::unique_ptr<TaskBase>> tasks;   
        mutable std::mutex                    mutex;   
        std::condition_variable cv;           
        std::atomic<bool>       shutdown;     
        std::atomic<size_t>     active_tasks; 
        launch                  exit_launch_; 
 
    public:
        ThreadPool(launch exit_launch = launch::close,
            size_t        num_threads = std::thread::hardware_concurrency()) :
            shutdown(false), active_tasks(0), exit_launch_(exit_launch) {
            if (num_threads == 0) num_threads = 2;
            for (size_t i = 0; i < num_threads; ++i) {
                workers.emplace_back([this] {
                    while (true) {
                        std::unique_ptr<TaskBase> task;
                        {
                            std::unique_lock<std::mutex> lock(mutex);
                            cv.wait(lock, [this] {
                                return shutdown.load(std::memory_order_acquire)
                                       || !tasks.empty();
                            });
                            if (shutdown.load(std::memory_order_acquire)
                                && tasks.empty())
                                return;
                            task = std::move(tasks.front());
                            tasks.pop();
                        }
                        active_tasks.fetch_add(1, std::memory_order_release);
                        try {
                            task->execute();
                            active_tasks.fetch_sub(
                                1, std::memory_order_release);
                            if (active_tasks.load(std::memory_order_acquire)
                                    == 0
                                && tasks.empty())
                                cv.notify_all();
                        } catch (...) {
                            active_tasks.fetch_sub(
                                1, std::memory_order_release);
                            if (active_tasks.load(std::memory_order_acquire)
                                    == 0
                                && tasks.empty())
                                cv.notify_all();
                        }
                    }
                });
            }
        }

        ThreadPool(size_t num_threads, launch exit_launch = launch::close) :
            ThreadPool(exit_launch, num_threads) {}

        ~ThreadPool() {
            if (exit_launch_ == launch::close)
                close();
            else
                abort();
        }

        template <class F, class... Args>
        auto submit(F &&f, Args &&...args) -> std::future< //
            decltype(std::forward<F>(f)(std::forward<Args>(args)...))> {
            using return_type
                = decltype(std::forward<F>(f)(std::forward<Args>(args)...));
            auto bound_task
                = std::bind(std::forward<F>(f), std::forward<Args>(args)...);
            std::packaged_task<return_type()> task(bound_task);
            std::future<return_type>          result = task.get_future();
            {
                std::lock_guard<std::mutex> lock(mutex);
                if (shutdown.load(std::memory_order_acquire))
                    throw AsyncError("ThreadPool is shutting down");
                tasks.emplace(std::unique_ptr<TaskBase>(
                    new Task<return_type>(std::move(task))));
            }
            cv.notify_one();
            return result;
        }

        template <class F, class Container>
        auto map(F &&func, const Container &items)
            -> std::vector<std::future<decltype(func(
                std::declval<typename Container::value_type>()))>> {
            using return_type = decltype(func(
                std::declval<typename Container::value_type>()));
            std::vector<std::future<return_type>> futures;
            futures.reserve(items.size());
            for (const auto &item : items)
                futures.push_back(submit(func, item));
            return futures;
        }

        void wait() {
            std::unique_lock<std::mutex> lock(mutex);
            cv.wait(lock, [this] {
                return tasks.empty()
                       && active_tasks.load(std::memory_order_acquire) == 0;
            });
        }

        size_t waiting_task_count() const {
            std::lock_guard<std::mutex> lock(mutex);
            return tasks.size();
        }

        size_t active_task_count() const {
            return active_tasks.load(std::memory_order_acquire);
        }

        size_t active_worker_count() const { return workers.size(); }

        void close() {
            shutdown.store(true, std::memory_order_release);
            cv.notify_all();
            wait();
            for (auto &worker : workers)
                if (worker.joinable()) worker.join();
        }

        void abort() {
            shutdown.store(true, std::memory_order_release);
            {
                std::lock_guard<std::mutex> lock(mutex);
                std::queue<std::unique_ptr<TaskBase>>().swap(tasks);
            }
            cv.notify_all();
            for (auto &worker : workers)
                if (worker.joinable()) worker.detach();
        }

        ThreadPool(const ThreadPool &) = delete;
        ThreadPool &operator=(const ThreadPool &) = delete;
        ThreadPool(ThreadPool &&) = delete;
        ThreadPool &operator=(ThreadPool &&) = delete;
    };
 
    namespace pool {
        inline ThreadPool &instance() {
            static ThreadPool exe;
            return exe;
        }

        template <class F, class... Args>
        inline auto submit(F &&f, Args &&...args) -> std::future< //
            decltype(std::forward<F>(f)(std::forward<Args>(args)...))> {
            return instance().submit(
                std::forward<F>(f), std::forward<Args>(args)...);
        }

        template <class F, class Container>
        inline auto
        map(F &&f, const Container &c) -> std::vector<std::future<decltype(f(
            std::declval<typename Container::value_type>()))>> {
            return instance().map(std::forward<F>(f), c);
        }

        inline void wait() {
            instance().wait();
        }

        inline size_t waiting_task_count() {
            return instance().waiting_task_count();
        }

        inline size_t active_task_count() {
            return instance().active_task_count();
        }

        inline size_t active_worker_count() {
            return instance().active_worker_count();
        }

        inline void close() {
            return instance().close();
        }

        inline void abort() {
            return instance().abort();
        }
    }

    template <class F, class... Args>
    inline auto async(F &&f, Args &&...args) -> std::future< //
        decltype(std::forward<F>(f)(std::forward<Args>(args)...))> {
        return pool::submit(std::forward<F>(f), std::forward<Args>(args)...);
    }
}