c++ - 获取错误的毫秒延迟值

Question

我试图获得 1 毫秒的延迟，但延迟增加了 15 倍。我还尝试过使用 Windows Sleep(1) 函数，它也给出了相同的结果。

为什么我没有得到精确的毫秒延迟？

它的工作延迟为 1 秒。

#include <iostream>
#include <Windows.h>
#include <thread>
#include <chrono>

void counter1();

auto main() -> int
{

    std::thread p(&counter1);
    p.join();
    return 0;
}

void counter1()
{
    int nStep = 0;
    const int STEP = 1000;
    auto start = std::chrono::high_resolution_clock::now();
    for (;;)
    {
        ++nStep; // incrementing every millisecond
        std::this_thread::sleep_for(std::chrono::milliseconds(1));
        if (nStep == STEP) {  // compares at second
            auto duration = std::chrono::high_resolution_clock::now() - start;
            std::cout << "counter took " <<
                std::chrono::duration_cast<std::chrono::seconds>(duration).count()
                << "seconds \n";
            start = std::chrono::high_resolution_clock::now();
            nStep = 0;
        }
    }
}

该程序的输出:/image/AVZDV.png

Answer 1

您没有得到预期的结果，因为您的期望落空了。 sleep_for 并不是等待确切的时间。来自 cppreference :

Blocks the execution of the current thread for at least the specified sleep_duration.

This function may block for longer than sleep_duration due to scheduling or resource contention delays.

The standard recommends that a steady clock is used to measure the duration. If an implementation uses a system clock instead, the wait time may also be sensitive to clock adjustments.

精确的计时通常需要专用硬件。对于台式机的 1 毫秒预期是相当乐观的。

最重要的是，您测量的时间不仅仅来自 sleep_for。