41 lines
1.6 KiB
Go
41 lines
1.6 KiB
Go
//go:build windows
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package platform
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import (
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"math/bits"
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"time"
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"unsafe"
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)
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var (
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_QueryPerformanceCounter = kernel32.NewProc("QueryPerformanceCounter")
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_QueryPerformanceFrequency = kernel32.NewProc("QueryPerformanceFrequency")
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)
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var qpcfreq uint64
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func init() {
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_, _, _ = _QueryPerformanceFrequency.Call(uintptr(unsafe.Pointer(&qpcfreq)))
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}
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// On Windows, time.Time handled in time package cannot have the nanosecond precision.
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// The reason is that by default, it doesn't use QueryPerformanceCounter[1], but instead, use "interrupt time"
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// which doesn't support nanoseconds precision (though it is a monotonic) [2, 3, 4, 5].
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//
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// [1] https://learn.microsoft.com/en-us/windows/win32/api/profileapi/nf-profileapi-queryperformancecounter
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// [2] https://github.com/golang/go/blob/0cd309e12818f988693bf8e4d9f1453331dcf9f2/src/runtime/sys_windows_amd64.s#L297-L298
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// [3] https://github.com/golang/go/blob/0cd309e12818f988693bf8e4d9f1453331dcf9f2/src/runtime/os_windows.go#L549-L551
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// [4] https://github.com/golang/go/blob/master/src/runtime/time_windows.h#L7-L13
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// [5] http://web.archive.org/web/20210411000829/https://wrkhpi.wordpress.com/2007/08/09/getting-os-information-the-kuser_shared_data-structure/
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//
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// Therefore, on Windows, we directly invoke the syscall for QPC instead of time.Now or runtime.nanotime.
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// See https://github.com/golang/go/issues/31160 for example.
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func nanotime() int64 {
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var counter uint64
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_, _, _ = _QueryPerformanceCounter.Call(uintptr(unsafe.Pointer(&counter)))
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hi, lo := bits.Mul64(counter, uint64(time.Second))
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nanos, _ := bits.Div64(hi, lo, qpcfreq)
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return int64(nanos)
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}
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