Porting Clock_Gettime to Windows

Porting clock_gettime to windows

You can implement a clock_gettime() replacement for windows as follows:

LARGE_INTEGER
getFILETIMEoffset()
{
    SYSTEMTIME s;
    FILETIME f;
    LARGE_INTEGER t;

    s.wYear = 1970;
    s.wMonth = 1;
    s.wDay = 1;
    s.wHour = 0;
    s.wMinute = 0;
    s.wSecond = 0;
    s.wMilliseconds = 0;
    SystemTimeToFileTime(&s, &f);
    t.QuadPart = f.dwHighDateTime;
    t.QuadPart <<= 32;
    t.QuadPart |= f.dwLowDateTime;
    return (t);
}

int
clock_gettime(int X, struct timeval *tv)
{
    LARGE_INTEGER           t;
    FILETIME            f;
    double                  microseconds;
    static LARGE_INTEGER    offset;
    static double           frequencyToMicroseconds;
    static int              initialized = 0;
    static BOOL             usePerformanceCounter = 0;

    if (!initialized) {
        LARGE_INTEGER performanceFrequency;
        initialized = 1;
        usePerformanceCounter = QueryPerformanceFrequency(&performanceFrequency);
        if (usePerformanceCounter) {
            QueryPerformanceCounter(&offset);
            frequencyToMicroseconds = (double)performanceFrequency.QuadPart / 1000000.;
        } else {
            offset = getFILETIMEoffset();
            frequencyToMicroseconds = 10.;
        }
    }
    if (usePerformanceCounter) QueryPerformanceCounter(&t);
    else {
        GetSystemTimeAsFileTime(&f);
        t.QuadPart = f.dwHighDateTime;
        t.QuadPart <<= 32;
        t.QuadPart |= f.dwLowDateTime;
    }

    t.QuadPart -= offset.QuadPart;
    microseconds = (double)t.QuadPart / frequencyToMicroseconds;
    t.QuadPart = microseconds;
    tv->tv_sec = t.QuadPart / 1000000;
    tv->tv_usec = t.QuadPart % 1000000;
    return (0);
}

clock_gettime: identifier not found in Visual Studio in Windows 10

Function clock_gettime() is defined by POSIX. Windows is not POSIX compliant.

Here's a link to old post of porting clock_gettime() to Windows.

For Windows I would use std::chrono library.

Simple example is :

 #include <chrono>
    auto start = std::chrono::high_resolution_clock::now();
    func();
    auto end = std::chrono::high_resolution_clock::now();

    std::chrono::duration<float> duration = end - start;
    printf("Duration : %f", duration.count());

Is clock_gettime() correctly implemented in MinGW GCC 8.2.0?

That loop should get optimized out to nothing at all, so with a low resolution clock (resolution is not necessarily individual nanoseconds; it may advance in much larger units which clock_getres should be able to tell you) 0 is a plausible result. But you have a few other bugs in your code like mixing CLOCK_THREAD_CPUTIME_ID with CLOCK_PROCESS_CPUTIME_ID and not checking the return value of clock_gettime (it might be telling you these clocks aren't supported).

Porting to windows sockets

You need to initialize it first before making any socket call.

int iResult; 
// Initialize Winsock 
iResult = WSAStartup(MAKEWORD(2,2), &wsaData); 
if (iResult != 0) 
{ 
   printf("WSAStartup failed: %d\n", iResult); 
   return 1; 
}

timespec equivalent for windows

See, for example, How to realise long-term high-resolution timing on windows using C++? and C++ Timer function to provide time in nano seconds.

I have done some testing with Cygwin under Windows XP: on my machine, the granularity of gettimeofday() is about 15 msecs (~1/64 secs). Which is quite coarse. And so is the granularity of:

* clock_t clock(void) (divisor CLOCKS_PER_SEC)
* clock_t times(struct tms *) (divisor sysconf(_SC_CLK_TCK))

Both divisors are 1000 (POSIX may have 1000000 for first).

Also, clock_getres(CLOCK_REALTIME,...) returns 15 msecs, so clock_gettime() is unlikely to help. And CLOCK_MONOTONIC and CLOCK_PROCESS_CPUTIME_ID don't work.

Other possibilites for Windows might be RDTSC; see the Wikipedia article. And HPET, which isn't available with Windows XP.

Also note in Linux, clock() is the process time, while in Windows it is the wall time.

So some sample code, both for standard Unix, and for CYGWIN code running under Windows, which gives a granularity of about 50 microsecs (on my machine). The return value is in seconds, and gives the number of seconds elapsed since the function was first called. (I belatedly realized this was in an answer I gave over a year ago).

#ifndef __CYGWIN32__
double RealElapsedTime(void) { // returns 0 seconds first time called
   static struct timeval t0;
   struct timeval tv;
   gettimeofday(&tv, 0);
   if (!t0.tv_sec)
      t0 = tv;
   return tv.tv_sec - t0.tv_sec + (tv.tv_usec - t0.tv_usec) / 1000000.;
}
#else
#include <windows.h>
double RealElapsedTime(void) { // granularity about 50 microsecs on my machine
   static LARGE_INTEGER freq, start;
   LARGE_INTEGER count;
   if (!QueryPerformanceCounter(&count))
      FatalError("QueryPerformanceCounter");
   if (!freq.QuadPart) { // one time initialization
      if (!QueryPerformanceFrequency(&freq))
         FatalError("QueryPerformanceFrequency");
      start = count;
   }
   return (double)(count.QuadPart - start.QuadPart) / freq.QuadPart;
}
#endif

How do I port code calling QueryPerformanceFrequency to Rust?

The direct solution to accessing Windows APIs is to use the winapi crate. In this case, call QueryPerformanceFrequency:

use std::mem;
use winapi::um::profileapi::QueryPerformanceFrequency;

fn freq() -> u64 {
    unsafe {
        let mut freq = mem::zeroed();
        QueryPerformanceFrequency(&mut freq);
        *freq.QuadPart() as u64
    }
}

fn main() {
    println!("Hello, world!");
}

[dependencies]
winapi = { version = "0.3.8", features = ["profileapi"] }

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hi-resolution MONOTONIC timer

I would use Instant as a monotonic timer and assume it's high-enough precision until proven otherwise.

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