C 定时器的实现

C++ 定时器

定时器中主要的数据结构

• 优先级任务队列：队列中存储任务，每个任务会添加时间戳，最近的时间戳的任务会先出队。
  
• 锁和条件变量：当有任务需要执行时，用于通知正在等待的线程从任务队列中取出任务执行。
  
• 线程池：各个任务会放在线程池中执行。
  

下面是相关代码：

class TimerQueue {
    public:
    struct InternalS {
        std::chrono::time_point<std::chrono::high_resolution_clock> time_point_;
        std::function<void()> func_;
        bool operator<(const InternalS& b) const { return time_point_ > b.time_point_; }
    };
    enum class RepeatedIdState { kInit = 0, kRunning = 1, kStop = 2 };
    private:
    std::priority_queue<InternalS> queue_;
    bool running_ = false;
    std::mutex mutex_;
    std::condition_variable cond_;
    wzq::ThreadPool thread_pool_;
    std::atomic<int> repeated_func_id_;
    wzq::ThreadSafeMap<int, RepeatedIdState> repeated_id_state_map_;
};

初始化

在构造函数中初始化，主要是配置好内部的线程池，线程池中常驻的线程数目前设为4。

TimerQueue() : running_(true), thread_pool_(wzq::ThreadPool::ThreadPoolConfig{4, 4, 40, std::chrono::seconds(4)}) {
    repeated_func_id_.store(0);
}

开启定时器功能

打开内部的线程池功能，用于执行放入定时器中的任务，同时新开一个线程，循环等待任务到来后送入线程池中执行。

bool Run() {
    bool ret = thread_pool_.Start();
    if (!ret) {
        return false;
    }
    std::thread([this]() { RunLocal(); }).detach();
    return true;
}
void RunLocal() {
    while (running_) {
        std::unique_lock<std::mutex> lock(mutex_);
        if (queue_.empty()) {
            cond_.wait(lock);
            continue;
        }
        auto s = queue_.top();
        auto diff = s.time_point_ - std::chrono::high_resolution_clock::now();
        if (std::chrono::duration_cast<std::chrono::milliseconds>(diff).count() > 0) {
            cond_.wait_for(lock, diff);
            continue;
        } else {
            queue_.pop();
            lock.unlock();
            thread_pool_.Run(std::move(s.func_));
        }
    }
}

关闭定时器功能

这里是使用running_标志位控制，标志位为false，调度线程的循环就会自动退出，就不会继续等待任务执行。

void Stop() {
    running_ = false;
    cond_.notify_all();
}

在某一时间点执行任务

根据时间戳构造InternalS，放入队列中：

template <typename F, typename... Args>
void AddFuncAtTimePoint(const std::chrono::time_point<std::chrono::high_resolution_clock>& time_point, F&& f,
                        Args&&... args) {
    InternalS s;
    s.time_point_ = time_point;
    s.func_ = std::bind(std::forward<F>(f), std::forward<Args>(args)...);
    std::unique_lock<std::mutex> lock(mutex_);
    queue_.push(s);
    cond_.notify_all();
}

在某段时间后执行任务

根据当前时间加上时间段构造出时间戳从而构造InternalS，放入队列中：

template <typename R, typename P, typename F, typename... Args>
void AddFuncAfterDuration(const std::chrono::duration<R, P>& time, F&& f, Args&&... args) {
    InternalS s;
    s.time_point_ = std::chrono::high_resolution_clock::now() + time;
    s.func_ = std::bind(std::forward<F>(f), std::forward<Args>(args)...);
    std::unique_lock<std::mutex> lock(mutex_);
    queue_.push(s);
    cond_.notify_all();
}

循环执行任务

首先为这个循环任务生成标识ID，外部可以通过ID来取消此任务继续执行，代码如下，内部以类似递归的方式循环执行任务。

template <typename R, typename P, typename F, typename... Args>
int AddRepeatedFunc(int repeat_num, const std::chrono::duration<R, P>& time, F&& f, Args&&... args) {
    int id = GetNextRepeatedFuncId();
    repeated_id_state_map_.Emplace(id, RepeatedIdState::kRunning);
    auto tem_func = std::bind(std::forward<F>(f), std::forward<Args>(args)...);
    AddRepeatedFuncLocal(repeat_num - 1, time, id, std::move(tem_func));
    return id;
}
int GetNextRepeatedFuncId() { return repeated_func_id_++; }
template <typename R, typename P, typename F>
void AddRepeatedFuncLocal(int repeat_num, const std::chrono::duration<R, P>& time, int id, F&& f) {
    if (!this->repeated_id_state_map_.IsKeyExist(id)) {
        return;
    }
    InternalS s;
    s.time_point_ = std::chrono::high_resolution_clock::now() + time;
    auto tem_func = std::move(f);
    s.repeated_id = id;
    s.func_ = [this, &tem_func, repeat_num, time, id]() {
        tem_func();
        if (!this->repeated_id_state_map_.IsKeyExist(id) || repeat_num == 0) {
            return;
        }
        AddRepeatedFuncLocal(repeat_num - 1, time, id, std::move(tem_func));
    };
    std::unique_lock<std::mutex> lock(mutex_);
    queue_.push(s);
    lock.unlock();
    cond_.notify_all();
}

取消循环任务的执行

定时器内部有repeated_id_state_map 数据结构，用于存储循环任务的ID，当取消任务执行时，将此ID从repeatedid_state_map中移除，循环任务就会自动取消。

void CancelRepeatedFuncId(int func_id) { repeated_id_state_map_.EraseKey(func_id); }

简单的测试代码

void TestTimerQueue() {
    TimerQueue q;
    q.Run();
    for (int i = 5; i < 15; ++i) {
        q.AddFuncAfterDuration(std::chrono::seconds(i + 1), [i]() { std::cout << "this is " << i << std::endl; });
        q.AddFuncAtTimePoint(std::chrono::high_resolution_clock::now() + std::chrono::seconds(1),
                             [i]() { std::cout << "this is " << i << " at " << std::endl; });
    }
    int id = q.AddRepeatedFunc(10, std::chrono::seconds(1), []() { std::cout << "func " << std::endl; });
    std::this_thread::sleep_for(std::chrono::seconds(4));
    q.CancelRepeatedFuncId(id);
    std::this_thread::sleep_for(std::chrono::seconds(30));
    q.Stop();
}