diff options
| -rw-r--r-- | libcxx/src/chrono.cpp | 21 |
1 files changed, 15 insertions, 6 deletions
diff --git a/libcxx/src/chrono.cpp b/libcxx/src/chrono.cpp index ea0a638acc5..1758e6ca2f3 100644 --- a/libcxx/src/chrono.cpp +++ b/libcxx/src/chrono.cpp @@ -177,16 +177,25 @@ steady_clock::now() _NOEXCEPT #elif defined(_LIBCPP_WIN32API) +// https://msdn.microsoft.com/en-us/library/windows/desktop/ms644905(v=vs.85).aspx says: +// If the function fails, the return value is zero. <snip> +// On systems that run Windows XP or later, the function will always succeed +// and will thus never return zero. + +static LARGE_INTEGER +__QueryPerformanceFrequency() +{ + LARGE_INTEGER val; + (void) QueryPerformanceFrequency(&val); + return val; +} + steady_clock::time_point steady_clock::now() _NOEXCEPT { - static LARGE_INTEGER freq; - static BOOL initialized = FALSE; - if (!initialized) - initialized = QueryPerformanceFrequency(&freq); // always succceeds + static const LARGE_INTEGER freq = __QueryPerformanceFrequency(); - LARGE_INTEGER counter; - QueryPerformanceCounter(&counter); + LARGE_INTEGER counter = __QueryPerformanceFrequency(); return time_point(duration(counter.QuadPart * nano::den / freq.QuadPart)); } |
