Adding FunctionalGauge

README.md

@@ -21,6 +21,9 @@ g := metrics.NewGauge()
 metrics.Register("bar", g)
 g.Update(47)
 
+r := NewRegistry()
+g := metrics.NewRegisteredFunctionalGauge("cache-evictions", r, func() int64 { return cache.getEvictionsCount() })
+
 s := metrics.NewExpDecaySample(1028, 0.015) // or metrics.NewUniformSample(1028)
 h := metrics.NewHistogram(s)
 metrics.Register("baz", h)

gauge.go

@@ -36,6 +36,25 @@ func NewRegisteredGauge(name string, r Registry) Gauge {
 	return c
 }
 
+// NewFunctionalGauge constructs a new FunctionalGauge.
+func NewFunctionalGauge(f func() int64) Gauge {
+	if UseNilMetrics {
+		return NilGauge{}
+	}
+	return &FunctionalGauge{value: f}
+}
+
+
+// NewRegisteredFunctionalGauge constructs and registers a new StandardGauge.
+func NewRegisteredFunctionalGauge(name string, r Registry, f func() int64) Gauge {
+	c := NewFunctionalGauge(f)
+	if nil == r {
+		r = DefaultRegistry
+	}
+	r.Register(name, c)
+	return c
+}
+
 // GaugeSnapshot is a read-only copy of another Gauge.
 type GaugeSnapshot int64
 
@@ -82,3 +101,20 @@ func (g *StandardGauge) Update(v int64) {
 func (g *StandardGauge) Value() int64 {
 	return atomic.LoadInt64(&g.value)
 }
+// FunctionalGauge returns value from given function
+type FunctionalGauge struct {
+	value func() int64
+}
+
+// Value returns the gauge's current value.
+func (g FunctionalGauge) Value() int64 {
+	return g.value()
+}
+
+// Snapshot returns the snapshot.
+func (g FunctionalGauge) Snapshot() Gauge { return GaugeSnapshot(g.Value()) }
+
+// Update panics.
+func (FunctionalGauge) Update(int64) {
+	panic("Update called on a FunctionalGauge")
+}

gauge_float64.go

@@ -38,6 +38,24 @@ func NewRegisteredGaugeFloat64(name string, r Registry) GaugeFloat64 {
 	return c
 }
 
+// NewFunctionalGauge constructs a new FunctionalGauge.
+func NewFunctionalGaugeFloat64(f func() float64) GaugeFloat64 {
+	if UseNilMetrics {
+		return NilGaugeFloat64{}
+	}
+	return &FunctionalGaugeFloat64{value: f}
+}
+
+// NewRegisteredFunctionalGauge constructs and registers a new StandardGauge.
+func NewRegisteredFunctionalGaugeFloat64(name string, r Registry, f func() float64) GaugeFloat64 {
+	c := NewFunctionalGaugeFloat64(f)
+	if nil == r {
+		r = DefaultRegistry
+	}
+	r.Register(name, c)
+	return c
+}
+
 // GaugeFloat64Snapshot is a read-only copy of another GaugeFloat64.
 type GaugeFloat64Snapshot float64
 
@@ -89,3 +107,21 @@ func (g *StandardGaugeFloat64) Value() float64 {
 	defer g.mutex.Unlock()
 	return g.value
 }
+
+// FunctionalGaugeFloat64 returns value from given function
+type FunctionalGaugeFloat64 struct {
+	value func() float64
+}
+
+// Value returns the gauge's current value.
+func (g FunctionalGaugeFloat64) Value() float64 {
+	return g.value()
+}
+
+// Snapshot returns the snapshot.
+func (g FunctionalGaugeFloat64) Snapshot() GaugeFloat64 { return GaugeFloat64Snapshot(g.Value()) }
+
+// Update panics.
+func (FunctionalGaugeFloat64) Update(float64) {
+	panic("Update called on a FunctionalGaugeFloat64")
+}

gauge_float64_test.go

@@ -36,3 +36,24 @@ func TestGetOrRegisterGaugeFloat64(t *testing.T) {
 		t.Fatal(g)
 	}
 }
+
+func TestFunctionalGaugeFloat64(t *testing.T) {
+	var counter float64
+	fg := NewFunctionalGaugeFloat64(func() float64 {
+		counter++
+		return counter
+	})
+	fg.Value()
+	fg.Value()
+	if counter != 2 {
+		t.Error("counter != 2")
+	}
+}
+
+func TestGetOrRegisterFunctionalGaugeFloat64(t *testing.T) {
+	r := NewRegistry()
+	NewRegisteredFunctionalGaugeFloat64("foo", r, func() float64 { return 47})
+	if g := GetOrRegisterGaugeFloat64("foo", r); 47 != g.Value() {
+		t.Fatal(g)
+	}
+}

gauge_test.go

@@ -35,3 +35,24 @@ func TestGetOrRegisterGauge(t *testing.T) {
 		t.Fatal(g)
 	}
 }
+
+func TestFunctionalGauge(t *testing.T) {
+	var counter int64
+	fg := NewFunctionalGauge(func() int64 {
+		counter++
+		return counter
+	})
+	fg.Value()
+	fg.Value()
+	if counter != 2 {
+		t.Error("counter != 2")
+	}
+}
+
+func TestGetOrRegisterFunctionalGauge(t *testing.T) {
+	r := NewRegistry()
+	NewRegisteredFunctionalGauge("foo", r, func() int64 { return 47})
+	if g := GetOrRegisterGauge("foo", r); 47 != g.Value() {
+		t.Fatal(g)
+	}
+}