20

我正在编写一个支持发送和接收超时的可移植 Socket 类...为了实现我正在使用的这些超时select()...但是，我有时需要知道我select()在 Linux 上被阻塞了多长时间将通过gettimeofday()在我调用之前和之后调用select()然后使用timersub()来计算增量来实现...

鉴于select()在 Windows 上接受struct timeval超时，我应该使用什么方法来替换 Windows 上的 gettimeofday()？

4

4 回答 4

25

我最终找到了这个页面：gettimeofday()function for Windows（现在通过 Wayback Machine），它gettimeofday()在 Windows 上有一个方便的、花哨的实现。它使用该GetSystemTimeAsFileTime()方法获得准确的时钟。

更新：这是“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，链接实现中有一个错字：

#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值0（他们假设微秒，而不是 100 纳秒间隔的数量）。此错字是通过Google 代码项目页面上的此评论发现的。要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 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;
}
于 2009-11-05T01:17:38.710 回答
4

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;  
}
于 2009-11-04T20:30:19.363 回答
1

在您的情况下，我将使用与平台无关的std::clock

于 2009-11-04T21:08:45.877 回答
1

您可以查看 QueryPerformanceCounter 和 QueryPerformanceFrequency。这些分辨率非常高——在某些硬件定时器上低至每十个周期一个滴答声。

于 2012-06-05T22:34:33.253 回答