/**
 * @Description  :
 * @Author       : chenht2022
 * @Date         : 2024-07-22 02:03:05
 * @Version      : 1.0.0
 * @LastEditors  : chenht2022
 * @LastEditTime : 2024-07-25 10:33:34
 * @Copyright (c) 2024 by KVCache.AI, All Rights Reserved.
 **/

#include "backend.h"

thread_local int Backend::thread_local_id = -1;

Backend::Backend(int max_thread_num) {
    max_thread_num_ = max_thread_num;
    thread_state_.resize(max_thread_num_);
    for (int i = 0; i < max_thread_num_; i++) {
        thread_state_[i].curr = std::make_unique<std::atomic<int>>();
        thread_state_[i].status =
            std::make_unique<std::atomic<ThreadStatus>>(ThreadStatus::WAITING);
    }
    workers_.resize(max_thread_num_);
    for (int i = 1; i < max_thread_num_; i++) {
        workers_[i] = std::thread(&Backend::worker_thread, this, i);
    }
}

Backend::~Backend() {
    for (int i = 0; i < max_thread_num_; i++) {
        thread_state_[i].status->store(ThreadStatus::EXIT,
                                       std::memory_order_release);
    }
    for (int i = 1; i < max_thread_num_; i++) {
        if (workers_[i].joinable()) {
            workers_[i].join();
        }
    }
}

int Backend::get_thread_num() { return max_thread_num_; }

void Backend::do_work_stealing_job(int task_num,
                                   std::function<void(int)> init_func,
                                   std::function<void(int)> compute_func,
                                   std::function<void(int)> finalize_func) {
    init_func_ = init_func;
    compute_func_ = compute_func;
    finalize_func_ = finalize_func;
    thread_num_ = std::min(max_thread_num_, task_num);
    int base = task_num / thread_num_;
    int remain = task_num % thread_num_;
    thread_state_[0].end = base + (0 < remain);

    // 为主线程设置 thread_local_id
    thread_local_id = 0;

    for (int i = 1; i < thread_num_; i++) {
        thread_state_[i].curr->store(thread_state_[i - 1].end,
                                     std::memory_order_relaxed);
        thread_state_[i].end = thread_state_[i - 1].end + base + (i < remain);
        thread_state_[i].status->store(ThreadStatus::WORKING,
                                       std::memory_order_release);
    }
    thread_state_[0].curr->store(0, std::memory_order_relaxed);
    thread_state_[0].status->store(ThreadStatus::WORKING,
                                   std::memory_order_release);
    process_tasks(0);
    for (int i = 1; i < thread_num_; i++) {
        while (thread_state_[i].status->load(std::memory_order_acquire) ==
               ThreadStatus::WORKING) {
        }
    }
}

void Backend::process_tasks(int thread_id) {
    if (init_func_ != nullptr) {
        init_func_(thread_id);
    }
    while (true) {
        int task_id = thread_state_[thread_id].curr->fetch_add(
            1, std::memory_order_acq_rel);
        if (task_id >= thread_state_[thread_id].end) {
            break;
        }
        compute_func_(task_id);
    }
    for (int t_offset = 1; t_offset < thread_num_; t_offset++) {
        int t_i = (thread_id + t_offset) % thread_num_;
        if (thread_state_[t_i].status->load(std::memory_order_acquire) !=
            ThreadStatus::WORKING) {
            continue;
        }
        while (true) {
            int task_id = thread_state_[t_i].curr->fetch_add(
                1, std::memory_order_acq_rel);
            if (task_id >= thread_state_[t_i].end) {
                break;
            }
            compute_func_(task_id);
        }
    }
    if (finalize_func_ != nullptr) {
        finalize_func_(thread_id);
    }
    thread_state_[thread_id].status->store(ThreadStatus::WAITING,
                                           std::memory_order_release);
}

void Backend::worker_thread(int thread_id) {
    auto start = std::chrono::steady_clock::now();
    thread_local_id = thread_id; // 设置线程本地变量
    while (true) {
        ThreadStatus status =
            thread_state_[thread_id].status->load(std::memory_order_acquire);
        if (status == ThreadStatus::WORKING) {
            process_tasks(thread_id);
            start = std::chrono::steady_clock::now();
        } else if (status == ThreadStatus::WAITING) {
            auto now = std::chrono::steady_clock::now();
            auto duration =
                std::chrono::duration_cast<std::chrono::milliseconds>(now -
                                                                      start)
                    .count();
            if (duration > 50) {
                std::this_thread::sleep_for(std::chrono::milliseconds(1));
            }
        } else if (status == ThreadStatus::EXIT) {
            return;
        }
    }
}