Use time.Since rather than time.Now().Sub (#1160)

Author: bvwells

examples/derived_gauges/README.md

@@ -131,7 +131,7 @@ func (q *queue) Size() int64 {
 func (q *queue) Elapsed() float64 {
 	q.mu.Lock()
 	defer q.mu.Unlock()
-	return time.Now().Sub(q.lastConsumed).Seconds()
+	return time.Since(q.lastConsumed).Seconds()
 }
 
 ```
@@ -254,7 +254,7 @@ func (q *queue) Size() int64 {
 func (q *queue) Elapsed() float64 {
 	q.mu.Lock()
 	defer q.mu.Unlock()
-	return time.Now().Sub(q.lastConsumed).Seconds()
+	return time.Since(q.lastConsumed).Seconds()
 }
 
 

examples/derived_gauges/derived_gauge.go

@@ -130,7 +130,7 @@ func (q *queue) Size() int64 {
 func (q *queue) Elapsed() float64 {
 	q.mu.Lock()
 	defer q.mu.Unlock()
-	return time.Now().Sub(q.lastConsumed).Seconds()
+	return time.Since(q.lastConsumed).Seconds()
 }
 
 // END tofloat64

internal/internal.go

@@ -33,5 +33,5 @@ var UserAgent = fmt.Sprintf("opencensus-go/%s", opencensus.Version())
 // end as a monotonic time.
 // See https://golang.org/pkg/time/#hdr-Monotonic_Clocks
 func MonotonicEndTime(start time.Time) time.Time {
-	return start.Add(time.Now().Sub(start))
+	return start.Add(time.Since(start))
 }

zpages/rpcz.go

@@ -205,7 +205,7 @@ func (s snapExporter) ExportView(vd *view.Data) {
 	if len(vd.Rows) == 0 {
 		return
 	}
-	ageSec := float64(time.Now().Sub(programStartTime)) / float64(time.Second)
+	ageSec := float64(time.Since(programStartTime)) / float64(time.Second)
 
 	computeRate := func(maxSec, x float64) float64 {
 		dur := ageSec