在Windows上，我应该使用什么替代gettimeofday()函数？

Question

在Windows上，我应该使用什么替代gettimeofday()函数？

21

我正在编写一个可移植的Socket类，支持发送和接收超时...为了实现这些超时，我正在使用select()....但是有时我需要知道我在select()内部被阻塞的时间长度，当然在Linux上，我会在调用select()之前和之后调用gettimeofday()，然后使用timersub()来计算时间差...

鉴于Windows上的select()接受struct timeval作为其超时参数，我应该使用什么方法来替换Windows上的gettimeofday()呢?

- dicroce

4个回答

4

如何考虑：

unsigned long start = GetTickCount();
// stuff that needs to be timed
unsigned long delta = GetTickCount() - start;

GetTickCount() 不是非常精确，但通常可以很好地工作。如果您看到很多0、16或31毫秒间隔，请尝试在更长的间隔时间内计时，或使用更精确的函数，例如timeGetTime。

我通常会这样做：

unsigned long deltastack;
int samples = 0;
float average;

unsigned long start = GetTickCount();
// stuff that needs to be timed
unsigned long delta = GetTickCount() - start;

deltastack += delta;
if (samples++ == 10)
{
   // total time divided by amount of samples
   average = (float)deltastack / 10.f;
   deltastack = 0;
   samples = 0;  
}

- knight666

3

GetTicksCount会在大约45.7天后翻转。 - Shay Erlichmen

14

@Shay：你看过Windows连续运行超过45天吗？好的，是的，我这么说有点无礼...... - Mark Ransom

GetTickCount 函数- 检索从系统启动开始经过的毫秒数，最多可达到 49.7 天。 - Dinei

1

在您的情况下，我会使用平台无关的std::clock。

- Shay Erlichmen

此函数不返回绝对时间参考。 - chmike

@chmike他没有说他需要一个绝对时间参考。 - Shay Erlichmen

1

你可以查看 QueryPerformanceCounter 和 QueryPerformanceFrequency。这些是非常高分辨率的计时器，有些硬件可以达到每十个周期一次的精度。

- Puppy

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- dicroce · Accepted Answer

我最终找到了这个页面：gettimeofday()函数适用于Windows（现在通过Wayback Machine），其中有一个方便的、漂亮的gettimeofday()在Windows上的实现。它使用GetSystemTimeAsFileTime()方法来获取准确的时钟。

更新：这里有一个替代的活动链接，来自“Unix到HPC Windows移植词典”gettimeofday()（现在通过Wayback Machine），指向OP所提到的实现。请注意，链接的实现中还有一个拼写错误。

#if defined(_MSC_VER) || defined(_MSC_EXTENSIONS)
  #define DELTA_EPOCH_IN_MICROSECS  11644473600000000Ui64 // WRONG
#else
  #define DELTA_EPOCH_IN_MICROSECS  11644473600000000ULL // WRONG
#endif

显示的值末尾缺少一个额外的0（它们假定是微秒，而不是100纳秒间隔的数量）。通过这条评论在Google代码项目页面上发现了此错误。下面显示了正确使用的值：

#if defined(_MSC_VER) || defined(_MSC_EXTENSIONS)
  #define DELTA_EPOCH_IN_MICROSECS  116444736000000000Ui64 // CORRECT
#else
  #define DELTA_EPOCH_IN_MICROSECS  116444736000000000ULL // CORRECT
#endif

PostgreSQL在Windows上实现的gettimeofday函数：

/*
 * gettimeofday.c
 *    Win32 gettimeofday() replacement
 *
 * src/port/gettimeofday.c
 *
 * Copyright (c) 2003 SRA, Inc.
 * Copyright (c) 2003 SKC, Inc.
 *
 * Permission to use, copy, modify, and distribute this software and
 * its documentation for any purpose, without fee, and without a
 * written agreement is hereby granted, provided that the above
 * copyright notice and this paragraph and the following two
 * paragraphs appear in all copies.
 *
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE TO ANY PARTY FOR DIRECT,
 * INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
 * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
 * DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * THE AUTHOR SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS
 * IS" BASIS, AND THE AUTHOR HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE,
 * SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 */

#include "c.h"

#include <sys/time.h>


/* FILETIME of Jan 1 1970 00:00:00. */
static const unsigned __int64 epoch = ((unsigned __int64) 116444736000000000ULL);

/*
 * timezone information is stored outside the kernel so tzp isn't used anymore.
 *
 * Note: this function is not for Win32 high precision timing purpose. See
 * elapsed_time().
 */
int
gettimeofday(struct timeval * tp, struct timezone * tzp)
{
    FILETIME    file_time;
    SYSTEMTIME  system_time;
    ULARGE_INTEGER ularge;

    GetSystemTime(&system_time);
    SystemTimeToFileTime(&system_time, &file_time);
    ularge.LowPart = file_time.dwLowDateTime;
    ularge.HighPart = file_time.dwHighDateTime;

    tp->tv_sec = (long) ((ularge.QuadPart - epoch) / 10000000L);
    tp->tv_usec = (long) (system_time.wMilliseconds * 1000);

    return 0;
}