Move stats counters into engine to eliminate hot path map lookup

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

main.go

@@ -11,7 +11,6 @@ import (
 	"os/signal"
 	"strconv"
 	"strings"
-	"sync"
 	"syscall"
 	"time"
 
@@ -32,8 +31,6 @@ type App struct {
 	artTargets    map[uint16]*net.UDPAddr
 	sacnTargets   map[uint16][]*net.UDPAddr
 	debug         bool
-	statsMu       sync.Mutex
-	stats         map[config.Universe]uint64
 }
 
 func main() {
@@ -150,7 +147,6 @@ func main() {
 		artTargets:  artTargets,
 		sacnTargets: sacnTargets,
 		debug:       *debug,
-		stats:       map[config.Universe]uint64{},
 	}
 
 	// Create ArtNet receiver if enabled
@@ -245,9 +241,6 @@ func (a *App) HandleDMX(src *net.UDPAddr, pkt *artnet.DMXPacket) {
 			src.IP, pkt.Universe, pkt.Sequence, pkt.Length)
 	}
 	u := config.Universe{Protocol: config.ProtocolArtNet, Number: uint16(pkt.Universe)}
-	a.statsMu.Lock()
-	a.stats[u]++
-	a.statsMu.Unlock()
 	a.sendOutputs(a.engine.Remap(u, pkt.Data))
 }
 
@@ -273,9 +266,6 @@ func (a *App) HandleSACN(universe uint16, data [512]byte) {
 		log.Printf("[<-sacn] universe=%d", universe)
 	}
 	u := config.Universe{Protocol: config.ProtocolSACN, Number: universe}
-	a.statsMu.Lock()
-	a.stats[u]++
-	a.statsMu.Unlock()
 	a.sendOutputs(a.engine.Remap(u, data))
 }
 
@@ -334,19 +324,13 @@ func (a *App) handleConfig(w http.ResponseWriter, r *http.Request) {
 }
 
 func (a *App) printStats() {
-	a.statsMu.Lock()
+	if len(a.cfg.Mappings) == 0 {
-	stats := a.stats
-	a.stats = map[config.Universe]uint64{}
-	a.statsMu.Unlock()
-
-	if len(stats) == 0 && len(a.cfg.Mappings) == 0 {
 		return
 	}
-
+	counts := a.engine.SwapStats()
 	log.Printf("[stats] mapping traffic (last 10s):")
 	for _, m := range a.cfg.Mappings {
-		count := stats[m.From.Universe]
+		log.Printf("[stats]   %s -> %s: %d packets", m.From, m.To, counts[m.From.Universe])
-		log.Printf("[stats]   %s -> %s: %d packets", m.From, m.To, count)
 	}
 }
 

remap/engine.go

@@ -2,6 +2,7 @@ package remap
 
 import (
 	"sync"
+	"sync/atomic"
 
 	"github.com/gopatchy/artmap/config"
 )
@@ -12,19 +13,30 @@ type Output struct {
 	Data     [512]byte
 }
 
+// sourceEntry holds mappings and stats for a source universe
+type sourceEntry struct {
+	mappings []config.NormalizedMapping
+	counter  atomic.Uint64
+}
+
 // Engine handles DMX channel remapping
 type Engine struct {
 	mappings []config.NormalizedMapping
-	bySource map[config.Universe][]config.NormalizedMapping
+	bySource map[config.Universe]*sourceEntry
 	state    map[config.Universe]*[512]byte
 	stateMu  sync.Mutex
 }
 
 // NewEngine creates a new remapping engine
 func NewEngine(mappings []config.NormalizedMapping) *Engine {
-	bySource := make(map[config.Universe][]config.NormalizedMapping)
+	bySource := map[config.Universe]*sourceEntry{}
 	for _, m := range mappings {
-		bySource[m.From] = append(bySource[m.From], m)
+		entry := bySource[m.From]
+		if entry == nil {
+			entry = &sourceEntry{}
+			bySource[m.From] = entry
+		}
+		entry.mappings = append(entry.mappings, m)
 	}
 
 	state := make(map[config.Universe]*[512]byte)
@@ -43,17 +55,18 @@ func NewEngine(mappings []config.NormalizedMapping) *Engine {
 
 // Remap applies mappings to incoming DMX data and returns outputs
 func (e *Engine) Remap(src config.Universe, srcData [512]byte) []Output {
-	mappings, ok := e.bySource[src]
+	entry := e.bySource[src]
-	if !ok {
+	if entry == nil {
 		return nil
 	}
+	entry.counter.Add(1)
 
 	e.stateMu.Lock()
 	defer e.stateMu.Unlock()
 
 	affected := make(map[config.Universe]bool)
 
-	for _, m := range mappings {
+	for _, m := range entry.mappings {
 		affected[m.To] = true
 		outState := e.state[m.To]
 
@@ -77,6 +90,15 @@ func (e *Engine) Remap(src config.Universe, srcData [512]byte) []Output {
 	return result
 }
 
+// SwapStats returns packet counts per source universe since last call and resets them
+func (e *Engine) SwapStats() map[config.Universe]uint64 {
+	result := map[config.Universe]uint64{}
+	for u, entry := range e.bySource {
+		result[u] = entry.counter.Swap(0)
+	}
+	return result
+}
+
 // SourceArtNetUniverses returns source ArtNet universe numbers (for discovery)
 func (e *Engine) SourceArtNetUniverses() []uint16 {
 	seen := make(map[uint16]bool)