os/windows/dlls.c

   1 #include "os/os.h"
   2
   3 #include <windows.h>
   4
   5 void os_clk_tck(long *clk_tck)
   6 {
   7         /*
   8          * The timer resolution is variable on Windows. Try to query it
   9          * or use 64 Hz, the clock frequency lower bound. See also
  10          * https://carpediemsystems.co.uk/2019/07/18/windows-system-timer-granularity/.
  11          */
  12         unsigned long minRes, maxRes, curRes;
  13         HMODULE lib;
  14         FARPROC queryTimer;
  15         FARPROC setTimer;
  16
  17         if (!(lib = LoadLibrary(TEXT("ntdll.dll"))) ||
  18                 !(queryTimer = GetProcAddress(lib, "NtQueryTimerResolution")) ||
  19                 !(setTimer = GetProcAddress(lib, "NtSetTimerResolution"))) {
  20                 dprint(FD_HELPERTHREAD,
  21                         "Failed to load ntdll library, set to lower bound 64 Hz\n");
  22                 *clk_tck = 64;
  23         } else {
  24                 queryTimer(&minRes, &maxRes, &curRes);
  25                 dprint(FD_HELPERTHREAD,
  26                         "minRes = %lu, maxRes = %lu, curRes = %lu\n",
  27                         minRes, maxRes, curRes);
  28
  29                 /* Use maximum resolution for most accurate timestamps */
  30                 setTimer(maxRes, 1, &curRes);
  31                 *clk_tck = (long) (10000000L / maxRes);
  32         }
  33 }