timeval: Use high resolution timestamps on Windows

- Use QueryPerformanceCounter on Windows Vista+

There is confusing info floating around that QueryPerformanceCounter
can leap etc, which might have been true long time ago, but no longer
the case nowadays (perhaps starting from WinXP?). Also, boost and
std::chrono::steady_clock use QueryPerformanceCounter in a similar way.

Prior to this change GetTickCount or GetTickCount64 was used, which has
lower resolution. That is still the case for <= XP.

Fixes https://github.com/curl/curl/issues/3309
Closes https://github.com/curl/curl/pull/3318

diff --git a/lib/timeval.c b/lib/timeval.c
index dce1a761e81d0439dda1c9cc6d4d37000112abac..2d7c782fa7e747147296ab7aec0799e7f522808c 100644 (file)
--- a/lib/timeval.c
+++ b/lib/timeval.c
@@ -21,29 +21,36 @@
  ***************************************************************************/
 
 #include "timeval.h"
+#include "system_win32.h"
 
 #if defined(WIN32) && !defined(MSDOS)
 
 struct curltime Curl_now(void)
 {
-  /*
-  ** GetTickCount() is available on _all_ Windows versions from W95 up
-  ** to nowadays. Returns milliseconds elapsed since last system boot,
-  ** increases monotonically and wraps once 49.7 days have elapsed.
-  */
   struct curltime now;
-#if !defined(_WIN32_WINNT) || !defined(_WIN32_WINNT_VISTA) || \
-    (_WIN32_WINNT < _WIN32_WINNT_VISTA) || \
-    (defined(__MINGW32__) && !defined(__MINGW64_VERSION_MAJOR))
-  DWORD milliseconds = GetTickCount();
-  now.tv_sec = milliseconds / 1000;
-  now.tv_usec = (milliseconds % 1000) * 1000;
-#else
-  ULONGLONG milliseconds = GetTickCount64();
-  now.tv_sec = (time_t) (milliseconds / 1000);
-  now.tv_usec = (unsigned int) (milliseconds % 1000) * 1000;
-#endif
-
+  static LARGE_INTEGER freq;
+  static int isVistaOrGreater = -1;
+  if(isVistaOrGreater == -1) {
+    if(Curl_verify_windows_version(6, 0, PLATFORM_WINNT,
+                                   VERSION_GREATER_THAN_EQUAL)) {
+      isVistaOrGreater = 1;
+      QueryPerformanceFrequency(&freq);
+    }
+    else
+      isVistaOrGreater = 0;
+  }
+  if(isVistaOrGreater == 1) { /* QPC timer might have issues pre-Vista */
+    LARGE_INTEGER count;
+    QueryPerformanceCounter(&count);
+    now.tv_sec = (time_t)(count.QuadPart / freq.QuadPart);
+    now.tv_usec =
+      (int)((count.QuadPart % freq.QuadPart) * 1000000 / freq.QuadPart);
+  }
+  else {
+    DWORD milliseconds = GetTickCount();
+    now.tv_sec = milliseconds / 1000;
+    now.tv_usec = (milliseconds % 1000) * 1000;
+  }
   return now;
 }