wakey wakey

wake_clock_windows.go

@@ -0,0 +1,41 @@
+//go:build windows
+
+package nebula
+
+import (
+	"sync"
+	"time"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+var (
+	procQueryInterruptTime         = windows.NewLazySystemDLL("kernelbase.dll").NewProc("QueryInterruptTime")
+	procQueryUnbiasedInterruptTime = windows.NewLazySystemDLL("kernel32.dll").NewProc("QueryUnbiasedInterruptTime")
+
+	// QueryInterruptTime needs Windows 10; probe once and stay dormant on anything older.
+	wakeClockAvailable = sync.OnceValue(func() bool {
+		return procQueryInterruptTime.Find() == nil && procQueryUnbiasedInterruptTime.Find() == nil
+	})
+)
+
+// suspendClockDelta returns interrupt time minus unbiased interrupt time, both in 100ns units. The unbiased count
+// excludes time the system spends suspended while the biased one includes it, so the difference grows by exactly
+// the time spent asleep.
+//
+// The pausing (unbiased) clock is read first so scheduling jitter between the two reads biases the delta positive;
+// the wakeDetector clamps out the noise.
+func suspendClockDelta() (time.Duration, bool) {
+	if !wakeClockAvailable() {
+		return 0, false
+	}
+
+	var unbiased, biased uint64
+	if r1, _, _ := procQueryUnbiasedInterruptTime.Call(uintptr(unsafe.Pointer(&unbiased))); r1 == 0 {
+		return 0, false
+	}
+	// Returns void, cannot fail once resolved.
+	_, _, _ = procQueryInterruptTime.Call(uintptr(unsafe.Pointer(&biased)))
+	return time.Duration(int64(biased-unbiased)) * 100, true
+}