all: use time.Since instead of time.Now().Sub

Change-Id: Ifaa73b64e5b6a1d37c753e2440b642478d7dfbce
Reviewed-on: https://go-review.googlesource.com/c/go/+/436957
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: hopehook <hopehook@golangcn.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

src/go/doc/testdata/benchmark.go

@@ -48,7 +48,7 @@ func (b *B) StartTimer() {
 // want to measure.
 func (b *B) StopTimer() {
 	if b.timerOn {
-		b.duration += time.Now().Sub(b.start)
+		b.duration += time.Since(b.start)
 		b.timerOn = false
 	}
 }

src/go/doc/testdata/example.go

@@ -59,7 +59,7 @@ func RunExamples(examples []InternalExample) (ok bool) {
 		// run example
 		t0 := time.Now()
 		eg.F()
-		dt := time.Now().Sub(t0)
+		dt := time.Since(t0)
 
 		// close pipe, restore stdout/stderr, get output
 		w.Close()

src/go/doc/testdata/testing.go

@@ -219,7 +219,7 @@ func tRunner(t *T, test *InternalTest) {
 	// a call to runtime.Goexit, record the duration and send
 	// a signal saying that the test is done.
 	defer func() {
-		t.duration = time.Now().Sub(t.start)
+		t.duration = time.Since(t.start)
 		t.signal <- t
 	}()
 

src/net/dial_test.go

@@ -171,7 +171,7 @@ func dialClosedPort(t *testing.T) (dialLatency time.Duration) {
 	if err == nil {
 		c.Close()
 	}
-	elapsed := time.Now().Sub(startTime)
+	elapsed := time.Since(startTime)
 	t.Logf("dialClosedPort: measured delay %v", elapsed)
 	return elapsed
 }
@@ -366,7 +366,7 @@ func TestDialerFallbackDelay(t *testing.T) {
 
 		startTime := time.Now()
 		c, err := d.Dial("tcp", JoinHostPort("slow6loopback4", dss.port))
-		elapsed := time.Now().Sub(startTime)
+		elapsed := time.Since(startTime)
 		if err == nil {
 			c.Close()
 		} else if tt.dualstack {

src/runtime/gc_test.go

@@ -689,7 +689,7 @@ func BenchmarkReadMemStatsLatency(b *testing.B) {
 		time.Sleep(100 * time.Millisecond)
 		start := time.Now()
 		runtime.ReadMemStats(&ms)
-		latencies = append(latencies, time.Now().Sub(start))
+		latencies = append(latencies, time.Since(start))
 	}
 	// Make sure to stop the timer before we wait! The load created above
 	// is very heavy-weight and not easy to stop, so we could end up

src/runtime/metrics_test.go

@@ -375,7 +375,7 @@ func BenchmarkReadMetricsLatency(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		start := time.Now()
 		metrics.Read(samples)
-		latencies = append(latencies, time.Now().Sub(start))
+		latencies = append(latencies, time.Since(start))
 	}
 	// Make sure to stop the timer before we wait! The load created above
 	// is very heavy-weight and not easy to stop, so we could end up

src/runtime/runtime_test.go

@@ -377,7 +377,7 @@ func BenchmarkGoroutineProfile(b *testing.B) {
 				if !ok {
 					b.Fatal("goroutine profile failed")
 				}
-				latencies = append(latencies, time.Now().Sub(start))
+				latencies = append(latencies, time.Since(start))
 			}
 			b.StopTimer()
 

src/runtime/testdata/testprog/gc.go

@@ -396,7 +396,7 @@ func gcMemoryLimit(gcPercent int) {
 		// should do considerably better than this bound.
 		bound := int64(myLimit + 16<<20)
 		start := time.Now()
-		for time.Now().Sub(start) < 200*time.Millisecond {
+		for time.Since(start) < 200*time.Millisecond {
 			metrics.Read(m[:])
 			retained := int64(m[0].Value.Uint64() - m[1].Value.Uint64())
 			if retained > bound {