我应该用什么来替换 Windows 上的 gettimeofday() ？

Question

我正在编写一个可移植的 Socket 类，它支持发送和接收超时...为了实现这些超时，我使用 select()...但是，我有时需要知道多长时间我被阻塞在 select() 内部，当然在 Linux 上我会通过在调用 select() 之前和之后调用 gettimeofday() 来实现然后使用 timersub() 计算增量...

鉴于 Windows 上的 select() 接受 struct timeval 作为超时，应该使用什么方法我曾经在 Windows 上替换 gettimeofday() ？

Answer 1

我最终找到了这个页面： gettimeofday() Windows 函数（现在通过 Wayback Machine），它有一个方便、花哨的 gettimeofday() 实现视窗。它使用 GetSystemTimeAsFileTime() 方法来获取准确的时钟。

更新：这是来自“Unix to Windows Porting Dictionary for HPC”的替代活动链接gettimeofday() （现在通过 Wayback Machine）指向 OP 引用的实现。另请注意，链接实现中存在拼写错误：

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

显示的值末尾缺少额外的 0 （它们假定为微秒，而不是 100 纳秒间隔的数量）。此拼写错误是通过此评论发现的谷歌代码项目页面。使用的正确值如下所示：

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

---

PostgreSQL 对 Windows 的 gettimeofday 实现：

/*
 * 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;
}

Answer 2

怎么样：

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

GetTickCount() 不是很精确，但可能会工作得很好。如果您看到大量 0、16 或 31 毫秒的间隔，请尝试计时更长的间隔或使用更精确的函数，例如 timeGetTime。

我通常做的是这样的：

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;  
}

Answer 3

在您的情况下，我将使用独立于平台的 std::clock

Answer 4

您可以查看 QueryPerformanceCounter 和 QueryPerformanceFrequency。这些分辨率非常 - 在某些硬件定时器上低至每十个周期一次。