Collect at every scrape, rather than at regular intervals.

Switch to Update using the Collecter Collect interface, due to not knowing all
metricnames in all modules beforehand we can't use Describe and thus the full
Collecter interface.

Remove 'updates', it's meaning varies by module and doesn't add much.

collector/stat.go

@@ -73,35 +73,14 @@ func NewStatCollector(config Config) (Collector, error) {
 	c := statCollector{
 		config: config,
 	}
-	if _, err := prometheus.RegisterOrGet(cpuMetrics); err != nil {
-		return nil, err
-	}
-	if _, err := prometheus.RegisterOrGet(intrMetric); err != nil {
-		return nil, err
-	}
-	if _, err := prometheus.RegisterOrGet(ctxtMetric); err != nil {
-		return nil, err
-	}
-	if _, err := prometheus.RegisterOrGet(forksMetric); err != nil {
-		return nil, err
-	}
-	if _, err := prometheus.RegisterOrGet(btimeMetric); err != nil {
-		return nil, err
-	}
-	if _, err := prometheus.RegisterOrGet(procsRunningMetric); err != nil {
-		return nil, err
-	}
-	if _, err := prometheus.RegisterOrGet(procsBlockedMetric); err != nil {
-		return nil, err
-	}
 	return &c, nil
 }
 
 // Expose a variety of stats from /proc/stats.
-func (c *statCollector) Update() (updates int, err error) {
+func (c *statCollector) Update(ch chan<- prometheus.Metric) (err error) {
 	file, err := os.Open(procStat)
 	if err != nil {
-		return updates, err
+		return err
 	}
 	defer file.Close()
 
@@ -119,7 +98,7 @@ func (c *statCollector) Update() (updates int, err error) {
 			for i, v := range parts[1 : len(cpuFields)+1] {
 				value, err := strconv.ParseFloat(v, 64)
 				if err != nil {
-					return updates, err
+					return err
 				}
 				// Convert from ticks to seconds
 				value /= float64(C.sysconf(C._SC_CLK_TCK))
@@ -129,40 +108,47 @@ func (c *statCollector) Update() (updates int, err error) {
 			// Only expose the overall number, use the 'interrupts' collector for more detail.
 			value, err := strconv.ParseFloat(parts[1], 64)
 			if err != nil {
-				return updates, err
+				return err
 			}
 			intrMetric.Set(value)
 		case parts[0] == "ctxt":
 			value, err := strconv.ParseFloat(parts[1], 64)
 			if err != nil {
-				return updates, err
+				return err
 			}
 			ctxtMetric.Set(value)
 		case parts[0] == "processes":
 			value, err := strconv.ParseFloat(parts[1], 64)
 			if err != nil {
-				return updates, err
+				return err
 			}
 			forksMetric.Set(value)
 		case parts[0] == "btime":
 			value, err := strconv.ParseFloat(parts[1], 64)
 			if err != nil {
-				return updates, err
+				return err
 			}
 			btimeMetric.Set(value)
 		case parts[0] == "procs_running":
 			value, err := strconv.ParseFloat(parts[1], 64)
 			if err != nil {
-				return updates, err
+				return err
 			}
 			procsRunningMetric.Set(value)
 		case parts[0] == "procs_blocked":
 			value, err := strconv.ParseFloat(parts[1], 64)
 			if err != nil {
-				return updates, err
+				return err
 			}
 			procsBlockedMetric.Set(value)
 		}
 	}
-	return updates, err
+	cpuMetrics.Collect(ch)
+	ctxtMetric.Collect(ch)
+	intrMetric.Collect(ch)
+	forksMetric.Collect(ch)
+	btimeMetric.Collect(ch)
+	procsRunningMetric.Collect(ch)
+	procsBlockedMetric.Collect(ch)
+	return err
 }