metrics: add force option for metric system (#17667)

metrics/ewma.go

@@ -17,9 +17,6 @@ type EWMA interface {
 
 // NewEWMA constructs a new EWMA with the given alpha.
 func NewEWMA(alpha float64) EWMA {
-	if !Enabled {
-		return NilEWMA{}
-	}
 	return &StandardEWMA{alpha: alpha}
 }
 

metrics/meter.go

@@ -29,6 +29,17 @@ func GetOrRegisterMeter(name string, r Registry) Meter {
 	return r.GetOrRegister(name, NewMeter).(Meter)
 }
 
+// GetOrRegisterMeterForced returns an existing Meter or constructs and registers a
+// new StandardMeter no matter the global switch is enabled or not.
+// Be sure to unregister the meter from the registry once it is of no use to
+// allow for garbage collection.
+func GetOrRegisterMeterForced(name string, r Registry) Meter {
+	if nil == r {
+		r = DefaultRegistry
+	}
+	return r.GetOrRegister(name, NewMeterForced).(Meter)
+}
+
 // NewMeter constructs a new StandardMeter and launches a goroutine.
 // Be sure to call Stop() once the meter is of no use to allow for garbage collection.
 func NewMeter() Meter {
@@ -46,8 +57,23 @@ func NewMeter() Meter {
 	return m
 }
 
-// NewMeter constructs and registers a new StandardMeter and launches a
+// NewMeterForced constructs a new StandardMeter and launches a goroutine no matter
-// goroutine.
+// the global switch is enabled or not.
+// Be sure to call Stop() once the meter is of no use to allow for garbage collection.
+func NewMeterForced() Meter {
+	m := newStandardMeter()
+	arbiter.Lock()
+	defer arbiter.Unlock()
+	arbiter.meters[m] = struct{}{}
+	if !arbiter.started {
+		arbiter.started = true
+		go arbiter.tick()
+	}
+	return m
+}
+
+// NewRegisteredMeter constructs and registers a new StandardMeter
+// and launches a goroutine.
 // Be sure to unregister the meter from the registry once it is of no use to
 // allow for garbage collection.
 func NewRegisteredMeter(name string, r Registry) Meter {
@@ -59,6 +85,19 @@ func NewRegisteredMeter(name string, r Registry) Meter {
 	return c
 }
 
+// NewRegisteredMeterForced constructs and registers a new StandardMeter
+// and launches a goroutine no matter the global switch is enabled or not.
+// Be sure to unregister the meter from the registry once it is of no use to
+// allow for garbage collection.
+func NewRegisteredMeterForced(name string, r Registry) Meter {
+	c := NewMeterForced()
+	if nil == r {
+		r = DefaultRegistry
+	}
+	r.Register(name, c)
+	return c
+}
+
 // MeterSnapshot is a read-only copy of another Meter.
 type MeterSnapshot struct {
 	count                          int64