Question

我正在编写一个便携式Socket类，支持发送和接收的超时...为了实现这些超时，我正在使用select() ....但是，我有时需要知道我有多久阻止在select()内部当然在Linux上我将通过在调用gettimeofday()之前和之后调用select()然后使用timersub()来计算delta ...来实现...

鉴于Windows上的select()接受struct timeval超时，我应该用什么方法替换Windows上的gettimeofday（）？

Answer 1

我最终找到了这个页面：windows上的gettimeofday（）[编辑：链接已删除，因为它现在指向一个广告网站]。它在Windows上有一个方便，花花公子的gettimeofday（）实现。它使用GetSystemTimeAsFileTime()方法获得准确的时钟。

更新：这是一个有效的链接[编辑：链接被删除，因为它现在指向一个广告网站]，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

显示的值在结尾处缺少额外的0（它们假定为微秒，而不是100纳秒间隔的数量）。此错误信息是通过Google代码项目页面上的this comment找到的。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为windows实现gettimeofday：

/*
 * 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，但可能效果很好。如果您看到很多0,16或31毫秒的间隔，请尝试更长的时间间隔或使用更精确的函数，如timeGetTime。

我通常做的是：

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，我会使用独立于平台的std::clock

Answer 4

您可以查看QueryPerformanceCounter和QueryPerformanceFrequency。这些非常高分辨率 - 在某些硬件定时器上每十个周期下降一个滴答。

我应该用什么来替换Windows上的gettimeofday（）？

4 个答案: