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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
This commit is contained in:
Pavel P 2018-11-26 15:10:10 -08:00 committed by Jay Satiro
parent c98ee5f67f
commit e9ababd4f5
1 changed files with 24 additions and 17 deletions
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41
lib/timeval.c
View File

@ -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;
}