metrics: pull library and introduce ResettingTimer and InfluxDB reporter (#15910)

* go-metrics: fork library and introduce ResettingTimer and InfluxDB reporter.

* vendor: change nonsense/go-metrics to ethersphere/go-metrics

* go-metrics: add tests. move ResettingTimer logic from reporter to type.

* all, metrics: pull in metrics package in go-ethereum

* metrics/test: make sure metrics are enabled for tests

* metrics: apply gosimple rules

* metrics/exp, internal/debug: init expvar endpoint when starting pprof server

* internal/debug: tiny comment formatting fix

metrics/runtime_test.go

@@ -0,0 +1,88 @@
+package metrics
+
+import (
+	"runtime"
+	"testing"
+	"time"
+)
+
+func BenchmarkRuntimeMemStats(b *testing.B) {
+	r := NewRegistry()
+	RegisterRuntimeMemStats(r)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		CaptureRuntimeMemStatsOnce(r)
+	}
+}
+
+func TestRuntimeMemStats(t *testing.T) {
+	r := NewRegistry()
+	RegisterRuntimeMemStats(r)
+	CaptureRuntimeMemStatsOnce(r)
+	zero := runtimeMetrics.MemStats.PauseNs.Count() // Get a "zero" since GC may have run before these tests.
+	runtime.GC()
+	CaptureRuntimeMemStatsOnce(r)
+	if count := runtimeMetrics.MemStats.PauseNs.Count(); 1 != count-zero {
+		t.Fatal(count - zero)
+	}
+	runtime.GC()
+	runtime.GC()
+	CaptureRuntimeMemStatsOnce(r)
+	if count := runtimeMetrics.MemStats.PauseNs.Count(); 3 != count-zero {
+		t.Fatal(count - zero)
+	}
+	for i := 0; i < 256; i++ {
+		runtime.GC()
+	}
+	CaptureRuntimeMemStatsOnce(r)
+	if count := runtimeMetrics.MemStats.PauseNs.Count(); 259 != count-zero {
+		t.Fatal(count - zero)
+	}
+	for i := 0; i < 257; i++ {
+		runtime.GC()
+	}
+	CaptureRuntimeMemStatsOnce(r)
+	if count := runtimeMetrics.MemStats.PauseNs.Count(); 515 != count-zero { // We lost one because there were too many GCs between captures.
+		t.Fatal(count - zero)
+	}
+}
+
+func TestRuntimeMemStatsNumThread(t *testing.T) {
+	r := NewRegistry()
+	RegisterRuntimeMemStats(r)
+	CaptureRuntimeMemStatsOnce(r)
+
+	if value := runtimeMetrics.NumThread.Value(); value < 1 {
+		t.Fatalf("got NumThread: %d, wanted at least 1", value)
+	}
+}
+
+func TestRuntimeMemStatsBlocking(t *testing.T) {
+	if g := runtime.GOMAXPROCS(0); g < 2 {
+		t.Skipf("skipping TestRuntimeMemStatsBlocking with GOMAXPROCS=%d\n", g)
+	}
+	ch := make(chan int)
+	go testRuntimeMemStatsBlocking(ch)
+	var memStats runtime.MemStats
+	t0 := time.Now()
+	runtime.ReadMemStats(&memStats)
+	t1 := time.Now()
+	t.Log("i++ during runtime.ReadMemStats:", <-ch)
+	go testRuntimeMemStatsBlocking(ch)
+	d := t1.Sub(t0)
+	t.Log(d)
+	time.Sleep(d)
+	t.Log("i++ during time.Sleep:", <-ch)
+}
+
+func testRuntimeMemStatsBlocking(ch chan int) {
+	i := 0
+	for {
+		select {
+		case ch <- i:
+			return
+		default:
+			i++
+		}
+	}
+}