From efb742b043153f7e0b8b2b2cff45534b26c6bfb9 Mon Sep 17 00:00:00 2001
From: Ling Yuan <lyuan@netflix.com>
Date: Mon, 11 Nov 2024 14:17:37 -0800
Subject: [PATCH] Optimize counter inc-by-one

Conceivably increment-by-one is by far the most common operation on counters.
This PR optimize such operation, making it alloc-free.

Benchmark with:
```
func BenchmarkInc(b *testing.B) {
	b.Run("Increment", func(b *testing.B) {
		w := writer.MemoryWriter{}
		id := NewId("foo", nil)
		c := NewCounter(id, &w)
		b.ReportAllocs()
		b.ResetTimer()
		for i := 0; i < b.N; i++ {
			c.Increment()
		}
	})
}
```

before optimization:
```
goos: darwin
goarch: arm64
pkg: github.com/Netflix/spectator-go/v2/spectator/meter
cpu: Apple M3 Pro
BenchmarkInc/Increment-12               10298648               115.2
ns/op           120 B/op          3 allocs/op
PASS
ok      github.com/Netflix/spectator-go/v2/spectator/meter      2.485s
```

after optimization:
```
goos: darwin
goarch: arm64
pkg: github.com/Netflix/spectator-go/v2/spectator/meter
cpu: Apple M3 Pro
BenchmarkInc/Increment-12               40374824                31.44
ns/op           97 B/op          0 allocs/op
PASS
ok      github.com/Netflix/spectator-go/v2/spectator/meter      3.563s
```
---
 spectator/meter/counter.go      | 19 +++++++++++--------
 spectator/meter/counter_test.go | 12 +++++++++---
 2 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/spectator/meter/counter.go b/spectator/meter/counter.go
index efd53e4..d19a710 100644
--- a/spectator/meter/counter.go
+++ b/spectator/meter/counter.go
@@ -13,14 +13,14 @@ import (
 //
 // https://netflix.github.io/spectator/en/latest/intro/counter/
 type Counter struct {
-	id              *Id
-	writer          writer.Writer
-	meterTypeSymbol string
+	id           *Id
+	writer       writer.Writer
+	incByOneLine string
 }
 
 // NewCounter generates a new counter, using the provided meter identifier.
 func NewCounter(id *Id, writer writer.Writer) *Counter {
-	return &Counter{id, writer, "c"}
+	return &Counter{id, writer, fmt.Sprintf("c:%s:1", id.spectatordId)}
 }
 
 // MeterId returns the meter identifier.
@@ -30,14 +30,17 @@ func (c *Counter) MeterId() *Id {
 
 // Increment increments the counter.
 func (c *Counter) Increment() {
-	var line = fmt.Sprintf("%s:%s:%d", c.meterTypeSymbol, c.id.spectatordId, 1)
-	c.writer.Write(line)
+	c.writer.Write(c.incByOneLine)
 }
 
 // Add adds an int64 delta to the current measurement.
 func (c *Counter) Add(delta int64) {
+	if delta == 1 {
+		c.writer.Write(c.incByOneLine)
+		return
+	}
 	if delta > 0 {
-		var line = fmt.Sprintf("%s:%s:%d", c.meterTypeSymbol, c.id.spectatordId, delta)
+		var line = fmt.Sprintf("c:%s:%d", c.id.spectatordId, delta)
 		c.writer.Write(line)
 	}
 }
@@ -45,7 +48,7 @@ func (c *Counter) Add(delta int64) {
 // AddFloat adds a float64 delta to the current measurement.
 func (c *Counter) AddFloat(delta float64) {
 	if delta > 0.0 {
-		var line = fmt.Sprintf("%s:%s:%f", c.meterTypeSymbol, c.id.spectatordId, delta)
+		var line = fmt.Sprintf("c:%s:%f", c.id.spectatordId, delta)
 		c.writer.Write(line)
 	}
 }
diff --git a/spectator/meter/counter_test.go b/spectator/meter/counter_test.go
index bd57947..fe1a314 100644
--- a/spectator/meter/counter_test.go
+++ b/spectator/meter/counter_test.go
@@ -23,15 +23,21 @@ func TestCounter_Add(t *testing.T) {
 	id := NewId("add", nil)
 	c := NewCounter(id, &w)
 
-	c.Add(4)
+	c.Add(1)
 
-	expected := "c:add:4"
+	expected := "c:add:1"
 	if w.Lines()[0] != expected {
 		t.Error("Expected ", expected, " got ", w.Lines()[0])
 	}
+	c.Add(4)
+
+	expected = "c:add:4"
+	if w.Lines()[1] != expected {
+		t.Error("Expected ", expected, " got ", w.Lines()[1])
+	}
 
 	c.Add(-1)
-	if len(w.Lines()) != 1 {
+	if len(w.Lines()) != 2 {
 		t.Error("Negative deltas should be ignored")
 	}
 }