tracing: NumSubscribers() to use atomic instead of mutex (#11219)

globalSubscribers.NumSubscribers() is heavily used in S3 requests and it
uses mutex, use atomic.Load instead since it is faster

Co-authored-by: Anis Elleuch <anis@min.io>

cmd/background-heal-ops.go

@@ -67,7 +67,7 @@ func waitForLowHTTPReq(maxIO int, maxWait time.Duration) {
 	// Bucket notification and http trace are not costly, it is okay to ignore them
 	// while counting the number of concurrent connections
 	maxIOFn := func() int {
-		return maxIO + globalHTTPListen.NumSubscribers() + globalHTTPTrace.NumSubscribers()
+		return maxIO + int(globalHTTPListen.NumSubscribers()) + int(globalHTTPTrace.NumSubscribers())
 	}
 
 	if httpServer := newHTTPServerFn(); httpServer != nil {

cmd/consolelogger.go

@@ -70,7 +70,7 @@ func (sys *HTTPConsoleLoggerSys) SetNodeName(endpointServerPools EndpointServerP
 // HasLogListeners returns true if console log listeners are registered
 // for this node or peers
 func (sys *HTTPConsoleLoggerSys) HasLogListeners() bool {
-	return sys != nil && sys.pubsub.HasSubscribers()
+	return sys != nil && sys.pubsub.NumSubscribers() > 0
 }
 
 // Subscribe starts console logging for this node.

cmd/handler-utils.go

@@ -348,7 +348,7 @@ func extractPostPolicyFormValues(ctx context.Context, form *multipart.Form) (fil
 // Log headers and body.
 func httpTraceAll(f http.HandlerFunc) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		if !globalHTTPTrace.HasSubscribers() {
+		if globalHTTPTrace.NumSubscribers() == 0 {
 			f.ServeHTTP(w, r)
 			return
 		}
@@ -360,7 +360,7 @@ func httpTraceAll(f http.HandlerFunc) http.HandlerFunc {
 // Log only the headers.
 func httpTraceHdrs(f http.HandlerFunc) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		if !globalHTTPTrace.HasSubscribers() {
+		if globalHTTPTrace.NumSubscribers() == 0 {
 			f.ServeHTTP(w, r)
 			return
 		}

cmd/notification.go

@@ -1375,7 +1375,7 @@ func sendEvent(args eventArgs) {
 		return
 	}
 
-	if globalHTTPListen.HasSubscribers() {
+	if globalHTTPListen.NumSubscribers() > 0 {
 		globalHTTPListen.Publish(args.ToEvent(false))
 	}
 

cmd/web-router.go

@@ -85,7 +85,7 @@ func registerWebRouter(router *mux.Router) error {
 				"bucket": bucketName,
 				"object": objectName,
 			})
-			if globalHTTPTrace.HasSubscribers() {
+			if globalHTTPTrace.NumSubscribers() > 0 {
 				globalHTTPTrace.Publish(WebTrace(ri))
 			}
 			logger.AuditLog(ri.ResponseWriter, ri.Request, ri.Method, claims.Map())

pkg/pubsub/pubsub.go

@@ -18,6 +18,7 @@ package pubsub
 
 import (
 	"sync"
+	"sync/atomic"
 )
 
 // Sub - subscriber entity.
@@ -28,7 +29,8 @@ type Sub struct {
 
 // PubSub holds publishers and subscribers
 type PubSub struct {
-	subs []*Sub
+	subs           []*Sub
+	numSubscribers int32
 	sync.RWMutex
 }
 
@@ -56,6 +58,7 @@ func (ps *PubSub) Subscribe(subCh chan interface{}, doneCh <-chan struct{}, filt
 
 	sub := &Sub{subCh, filter}
 	ps.subs = append(ps.subs, sub)
+	atomic.AddInt32(&ps.numSubscribers, 1)
 
 	go func() {
 		<-doneCh
@@ -68,19 +71,13 @@ func (ps *PubSub) Subscribe(subCh chan interface{}, doneCh <-chan struct{}, filt
 				ps.subs = append(ps.subs[:i], ps.subs[i+1:]...)
 			}
 		}
+		atomic.AddInt32(&ps.numSubscribers, -1)
 	}()
 }
 
-// HasSubscribers returns true if pubsub system has subscribers
-func (ps *PubSub) HasSubscribers() bool {
-	return ps.NumSubscribers() > 0
-}
-
 // NumSubscribers returns the number of current subscribers
-func (ps *PubSub) NumSubscribers() int {
-	ps.RLock()
-	defer ps.RUnlock()
-	return len(ps.subs)
+func (ps *PubSub) NumSubscribers() int32 {
+	return atomic.LoadInt32(&ps.numSubscribers)
 }
 
 // New inits a PubSub system