Author: compnerd Date: Sun Jan 1 14:20:41 2017 New Revision: 290803 URL: http://llvm.org/viewvc/llvm-project?rev=290803&view=rev Log: chrono: implement a Windows version of system_clock::now
system_clock::now is not entirely straight forward on Windows, which does not have a clock_gettime function. GetSystemTimeAsFileTime gives us the value relative to the NT epoch (Jan 1 1601) rather than the Unix epoch (Jan 1 1970). However, this function has a low resolution (~10ms). Newer versions of Windows provide GetSystemTimePreciseAsFileTime which gives us a much more accurate time (<1us). Unfortunately, the latter is only available on Windows 8+ when targeting desktop apps. Modified: libcxx/trunk/src/chrono.cpp Modified: libcxx/trunk/src/chrono.cpp URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/src/chrono.cpp?rev=290803&r1=290802&r2=290803&view=diff ============================================================================== --- libcxx/trunk/src/chrono.cpp (original) +++ libcxx/trunk/src/chrono.cpp Sun Jan 1 14:20:41 2017 @@ -12,9 +12,18 @@ #include "system_error" // __throw_system_error #include <time.h> // clock_gettime, CLOCK_MONOTONIC and CLOCK_REALTIME +#if defined(_WIN32) +#define WIN32_LEAN_AND_MEAN +#define VC_EXTRA_LEAN +#include <Windows.h> +#if _WIN32_WINNT >= _WIN32_WINNT_WIN8 +#include <winapifamily.h> +#endif +#else #if !defined(CLOCK_REALTIME) #include <sys/time.h> // for gettimeofday and timeval #endif +#endif #if !defined(_LIBCPP_HAS_NO_MONOTONIC_CLOCK) && !defined(CLOCK_MONOTONIC) #if __APPLE__ @@ -36,6 +45,28 @@ const bool system_clock::is_steady; system_clock::time_point system_clock::now() _NOEXCEPT { +#if defined(_WIN32) + // The Windows epoch is Jan 1 1601, the Unix epoch Jan 1 1970. The difference + // in nanoseconds is the windows epoch offset. + static const constexpr __int64 kWindowsEpochOffset = 0x19db1ded53e8000; + + FILETIME ftSystemTime; +#if _WIN32_WINNT >= _WIN32_WINNT_WIN8 +#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP) + GetSystemTimePreciseAsFileTime(&ftSystemTime); +#else + GetSystemTimeAsFileTime(&ftSystemTime); +#endif +#else + GetSystemTimeAsFileTime(&ftSystemTime); +#endif + __int64 llWinTimeNS = + ((static_cast<__int64>(ftSystemTime.dwHighDateTime) << 32) | + static_cast<__int64>(ftSystemTime.dwLowDateTime)) * + 100; + return time_point(duration_cast<duration>( + (nanoseconds(llWinTimeNS - kWindowsEpochOffset)))); +#else #ifdef CLOCK_REALTIME struct timespec tp; if (0 != clock_gettime(CLOCK_REALTIME, &tp)) @@ -46,6 +77,7 @@ system_clock::now() _NOEXCEPT gettimeofday(&tv, 0); return time_point(seconds(tv.tv_sec) + microseconds(tv.tv_usec)); #endif // CLOCK_REALTIME +#endif } time_t _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits