精确延迟Sleep

这代码是从OBS源码中扣出来的。

realtime.h

uint64_t os_gettime_ns(void);
bool os_sleepto_ns(uint64_t time_target);

realtime.cpp

#include "realSleep.h"

static inline uint64_t util_mul_div64(uint64_t num, uint64_t mul, uint64_t div)
{
#if defined(_MSC_VER) && defined(_M_X64) && (_MSC_VER >= 1920)
    unsigned __int64 high;
    const unsigned __int64 low = _umul128(num, mul, &high);
    unsigned __int64 rem;
    return _udiv128(high, low, div, &rem);
#else
    const uint64_t rem = num % div;
    return (num / div) * mul + (rem * mul) / div;
#endif
}

#define MAX_SZ_LEN 256
static bool have_clockfreq = false;
static LARGE_INTEGER clock_freq;
static uint32_t winver = 0;
static char win_release_id[MAX_SZ_LEN] = "unavailable";

static inline uint64_t get_clockfreq(void)
{
    if (!have_clockfreq) {
        QueryPerformanceFrequency(&clock_freq);
        have_clockfreq = true;
    }

    return clock_freq.QuadPart;
}

uint64_t os_gettime_ns(void)
{
    LARGE_INTEGER current_time;
    QueryPerformanceCounter(&current_time);
    return util_mul_div64(current_time.QuadPart, 1000000000,
        get_clockfreq());
}

bool os_sleepto_ns(uint64_t time_target)
{
    const uint64_t freq = get_clockfreq();
    const LONGLONG count_target = util_mul_div64(time_target, freq, 1000000000);

    LARGE_INTEGER count;
    QueryPerformanceCounter(&count);

    const bool stall = count.QuadPart < count_target;
    if (stall)
    {
        const DWORD milliseconds = (DWORD)(((count_target - count.QuadPart) * 1000.0) / freq);
        if (milliseconds > 1)
            Sleep(milliseconds - 1);

        for (;;)
        {
            QueryPerformanceCounter(&count);
            if (count.QuadPart >= count_target)
                break;

            YieldProcessor();
        }
    }

    return stall;
}

使用方法：

    uint64_t cur_time = os_gettime_ns();
    uint64_t ms =  1000 * 1000;
    ms = ms * 40;
    for (int i = 0;; i++)
    {
        memset(p, i % 256, len);
        m_usb.SetYUV2Data(p, len, &rtn);

        //40ms
        os_sleepto_ns(cur_time += ms);
    }