Add CPU usage tracker for Windows (fixes #729)

cmd/syncthing/gui_windows.go

@@ -0,0 +1,52 @@
+// Copyright (C) 2014 Jakob Borg and Contributors (see the CONTRIBUTORS file).
+// All rights reserved. Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+
+//+build windows
+
+package main
+
+import (
+	"syscall"
+	"time"
+)
+
+func init() {
+	go trackCPUUsage()
+}
+
+func trackCPUUsage() {
+	handle, err := syscall.GetCurrentProcess()
+	if err != nil {
+		l.Warnln("Cannot track CPU usage:", err)
+		return
+	}
+
+	var ctime, etime, ktime, utime syscall.Filetime
+	err = syscall.GetProcessTimes(handle, &ctime, &etime, &ktime, &utime)
+	if err != nil {
+		l.Warnln("Cannot track CPU usage:", err)
+		return
+	}
+
+	prevTime := ctime.Nanoseconds()
+	prevUsage := ktime.Nanoseconds() + utime.Nanoseconds() // Always overflows
+
+	for _ = range time.NewTicker(time.Second).C {
+		err := syscall.GetProcessTimes(handle, &ctime, &etime, &ktime, &utime)
+		if err != nil {
+			continue
+		}
+
+		curTime := time.Now().UnixNano()
+		timeDiff := curTime - prevTime
+		curUsage := ktime.Nanoseconds() + utime.Nanoseconds()
+		usageDiff := curUsage - prevUsage
+		cpuUsageLock.Lock()
+		copy(cpuUsagePercent[1:], cpuUsagePercent[0:])
+		cpuUsagePercent[0] = 100 * float64(usageDiff) / float64(timeDiff)
+		cpuUsageLock.Unlock()
+		prevTime = curTime
+		prevUsage = curUsage
+	}
+}