我正在编写一个支持发送和接收超时的可移植 Socket 类...为了实现这些超时，我使用select()...。但是，有时我需要知道我在里面被阻塞了多长时间select() 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() 来计算增量...
鉴于 Windows 上的 select() 接受 struct timeval 超时，我应该使用什么方法来替换 Windows 上的 gettimeofday()？
【问题讨论】：
标签： windows select winapi gettimeofday
我最终找到了这个页面：gettimeofday() function for Windows（现在通过 Wayback Machine），它在 Windows 上有一个方便、漂亮的 gettimeofday() 实现。它使用GetSystemTimeAsFileTime() 方法来获取准确的时钟。
更新：这是来自“Unix 到 HPC 的 Windows 移植字典”gettimeofday()（现在通过 Wayback Machine）的另一个活动链接，它指向 OP 所指的实现。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
显示的值最后缺少一个额外的0（它们假定为微秒，而不是 100 纳秒间隔的数量）。这个错字是在 Google 代码项目页面上通过 this comment 找到的。正确使用的值如下所示：
#if defined(_MSC_VER) || defined(_MSC_EXTENSIONS)
#define DELTA_EPOCH_IN_MICROSECS 116444736000000000Ui64 // CORRECT
#else
#define DELTA_EPOCH_IN_MICROSECS 116444736000000000ULL // CORRECT
#endif
PostgreSQL 在 Windows 上的 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;
}
【讨论】：
怎么样：
unsigned long start = GetTickCount();
// stuff that needs to be timed
unsigned long delta = GetTickCount() - start;
GetTickCount() 不是很精确，但可能会很好用。如果您看到很多 0、16 或 31 毫秒的时间间隔，请尝试在更长的时间间隔内计时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;
}
【讨论】：
在你的情况下，我会使用独立于平台的std::clock
【讨论】：
您可以查看 QueryPerformanceCounter 和 QueryPerformanceFrequency。这些是非常高分辨率 - 在某些硬件计时器上低至每十个周期一个滴答声。
【讨论】：