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         NTSTATUS NTAPI (*queryTimer)
  15                 (OUT PULONG              MinimumResolution,
  16                  OUT PULONG              MaximumResolution,
  17                  OUT PULONG              CurrentResolution);
  18         NTSTATUS NTAPI (*setTimer)
  19                 (IN ULONG                DesiredResolution,
  20                  IN BOOLEAN              SetResolution,
  21                  OUT PULONG              CurrentResolution);
  22
  23         if (!(lib = LoadLibrary(TEXT("ntdll.dll"))) ||
  24                 !(queryTimer = (void *)GetProcAddress(lib, "NtQueryTimerResolution")) ||
  25                 !(setTimer = (void *)GetProcAddress(lib, "NtSetTimerResolution"))) {
  26                 dprint(FD_HELPERTHREAD,
  27                         "Failed to load ntdll library, set to lower bound 64 Hz\n");
  28                 *clk_tck = 64;
  29         } else {
  30                 queryTimer(&minRes, &maxRes, &curRes);
  31                 dprint(FD_HELPERTHREAD,
  32                         "minRes = %lu, maxRes = %lu, curRes = %lu\n",
  33                         minRes, maxRes, curRes);
  34
  35                 /* Use maximum resolution for most accurate timestamps */
  36                 setTimer(maxRes, 1, &curRes);
  37                 *clk_tck = (long) (10000000L / maxRes);
  38         }
  39 }