每1秒调用一次函数(精确地) [英] Calling a function every 1 second (precisely)

问题描述

我正在使用C ++开发一个简单的游戏模拟程序，有一个名为update()的函数可以更新游戏的当前状态，必须每1秒钟精确调用一次.如果我使用这样的循环:

I am working on a simple game simulation program in C++, there's a function called update() that updates the current state of the game, it has to be called every 1 second precisely. If I use a loop like this:

while(//some condition) {
     update();
     Sleep(1000);
}

然后，该函数将不会每隔1秒调用一次，而是每隔(1 + update()的执行时间)调用一次. 我了解了各种解决方案，例如异步函数，多线程或使用std :: chrono计算函数的执行时间，并将其从1000ms参数中减去以进行睡眠.对于我的简单案例而言，其中一些过于复杂，如果我不太了解它们，则其他一些使用起来似乎是不安全的.

Then the function will not be called every 1 second, instead, every (1 + execution time of update () ). I read about various solutions like async functions, multithreading, or calculating the function's execution time using std::chrono and subtracting it from the 1000ms parameter to sleep. Some of those were too complicated for my simple case, and others seemed unsafe to use if I don't understand them really well.

谁能告诉我什么是适合我要求的解决方案? 预先感谢.

Can anyone tell me what would be a suitable solution to my requirement? Thanks in advance.

推荐答案

除了需要长时间睡眠外，您还需要直到某个时间点进行睡眠.例如，如果您的第一次更新恰好是2:00:00.000，则您以后的更新应尽可能接近2:00:01.000、2:00:02.000等.

Instead of sleeping for a duration, you need to sleep until a time point. For example, if your first update is at precisely 2:00:00.000, your future updates should come as closely as possible to 2:00:01.000, 2:00:02.000, etc.

要实现此目的，您可以指定一个线程进行更新，并且在更新之后，下次进入睡眠状态直到下一次进行计划的更新. chrono::system_clock::time_point和this_thread::sleep_until是执行此操作的工具.

To achieve this you can dedicate a thread to updating, and after the update, goes to sleep until the next time to do a scheduled update. chrono::system_clock::time_point and this_thread::sleep_until are your tools to do this.

例如:

#include <atomic>
#include <chrono>
#include <iostream>
#include <thread>

class UpdateManager
{
public:
    explicit UpdateManager() = default;

private:
    static std::atomic<int> now_;
    static std::atomic<bool> stop_;

    struct update_thread
        : private std::thread
    {
        ~update_thread();
        update_thread(update_thread&&) = default;

        using std::thread::thread;
    };

public:
    static update_thread start();
};

void update();

// source

std::atomic<int>  UpdateManager::now_{0};
std::atomic<bool> UpdateManager::stop_{false};

UpdateManager::update_thread::~update_thread()
{
    if (joinable())
    {
        stop_ = true;
        join();
    }
}

UpdateManager::update_thread
UpdateManager::start()
{
    return update_thread{[]
                         {
                             using namespace std;
                             using namespace std::chrono;
                             auto next = system_clock::now() + 1s;
                             while (!stop_)
                             {
                                 update();
                                 this_thread::sleep_until(next);
                                 next += 1s;
                             }
                         }};
}

#include "date/date.h"

void
update()
{
    using namespace date;
    using namespace std;
    using namespace std::chrono;
    cerr << system_clock::now() << '\n';
}

// demo

int
main()
{
    auto t = UpdateManager::start();
    using namespace std;
    this_thread::sleep_for(10s);
}

仅出于演示目的(对于逻辑不是必需的)，我使用的是 Howard Hinnant，免费的开源日期/时间库，以微秒为单位打印当前时间(UTC)，以说明该技术的稳定性.该程序的示例输出为:

Just for demo purposes (not necessary for the logic), I'm using Howard Hinnant's, free, open-source date/time library to print the current time (UTC) to microsecond precision in order to illustrate the stability of this technique. A sample output of this program is:

2018-05-02 15:14:25.634809
2018-05-02 15:14:26.637934
2018-05-02 15:14:27.636629
2018-05-02 15:14:28.637947
2018-05-02 15:14:29.638413
2018-05-02 15:14:30.639437
2018-05-02 15:14:31.637217
2018-05-02 15:14:32.637895
2018-05-02 15:14:33.637749
2018-05-02 15:14:34.639084

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