Remove unnecessary return, refactor permission check so that it doesn't hold locks longer than needed

Signed-off-by: Neil Twigg <neil@nats.io>

server/mqtt.go

@@ -23,6 +23,7 @@ import (
 	"io"
 	"net"
 	"net/http"
+	"sort"
 	"strconv"
 	"strings"
 	"sync"
@@ -1875,7 +1876,7 @@ func (as *mqttAccountSessionManager) sendJSAPIrequests(s *Server, c *client, acc
 // or 0 if the record was added instead of updated.
 //
 // Lock not held on entry.
-func (as *mqttAccountSessionManager) handleRetainedMsg(key string, rm *mqttRetainedMsgRef) uint64 {
+func (as *mqttAccountSessionManager) handleRetainedMsg(key string, rm *mqttRetainedMsgRef) {
 	as.mu.Lock()
 	defer as.mu.Unlock()
 	if as.retmsgs == nil {
@@ -1887,10 +1888,9 @@ func (as *mqttAccountSessionManager) handleRetainedMsg(key string, rm *mqttRetai
 			// If the new sequence is below the floor or the existing one,
 			// then ignore the new one.
 			if rm.sseq <= erm.sseq || rm.sseq <= erm.floor {
-				return 0
+				return
 			}
 			// Capture existing sequence number so we can return it as the old sequence.
-			oldSeq := erm.sseq
 			erm.sseq = rm.sseq
 			// Clear the floor
 			erm.floor = 0
@@ -1900,13 +1900,11 @@ func (as *mqttAccountSessionManager) handleRetainedMsg(key string, rm *mqttRetai
 				erm.sub = &subscription{subject: []byte(key)}
 				as.sl.Insert(erm.sub)
 			}
-			return oldSeq
 		}
 	}
 	rm.sub = &subscription{subject: []byte(key)}
 	as.retmsgs[key] = rm
 	as.sl.Insert(rm.sub)
-	return 0
 }
 
 // Removes the retained message for the given `subject` if present, and returns the
@@ -3256,15 +3254,43 @@ func (s *Server) mqttCheckPubRetainedPerms() {
 	}
 	s.mu.Unlock()
 
+	// First get a list of all of the sessions.
 	sm.mu.RLock()
-	defer sm.mu.RUnlock()
-
+	asms := make([]*mqttAccountSessionManager, 0, len(sm.sessions))
 	for _, asm := range sm.sessions {
+		asms = append(asms, asm)
+	}
+	sm.mu.RUnlock()
+
+	type retainedMsg struct {
+		subj string
+		rmsg *mqttRetainedMsgRef
+	}
+
+	// For each session we will obtain a list of retained messages.
+	var _rms [128]retainedMsg
+	rms := _rms[:0]
+	for _, asm := range asms {
+		// Get all of the retained messages. Then we will sort them so
+		// that they are in sequence order, which should help the file
+		// store to not have to load out-of-order blocks so often.
+		asm.mu.Lock()
+		rms = rms[:0] // reuse slice
+		for subj, rf := range asm.retmsgs {
+			rms = append(rms, retainedMsg{
+				subj: subj,
+				rmsg: rf,
+			})
+		}
+		asm.mu.Unlock()
+		sort.Slice(rms, func(i, j int) bool {
+			return rms[i].rmsg.sseq < rms[j].rmsg.sseq
+		})
+
 		perms := map[string]*perm{}
 		deletes := map[string]uint64{}
-		asm.mu.Lock()
-		for subject, rf := range asm.retmsgs {
-			jsm, err := asm.jsa.loadMsg(mqttRetainedMsgsStreamName, rf.sseq)
+		for _, rf := range rms {
+			jsm, err := asm.jsa.loadMsg(mqttRetainedMsgsStreamName, rf.rmsg.sseq)
 			if err != nil || jsm == nil {
 				continue
 			}
@@ -3285,7 +3311,7 @@ func (s *Server) mqttCheckPubRetainedPerms() {
 				}
 				// If there is permission and no longer allowed to publish in
 				// the subject, remove the publish retained message from the map.
-				if p != nil && !pubAllowed(p, subject) {
+				if p != nil && !pubAllowed(p, rf.subj) {
 					u = nil
 				}
 			}
@@ -3293,12 +3319,12 @@ func (s *Server) mqttCheckPubRetainedPerms() {
 			// Not present or permissions have changed such that the source can't
 			// publish on that subject anymore: remove it from the map.
 			if u == nil {
-				delete(asm.retmsgs, subject)
-				asm.sl.Remove(rf.sub)
-				deletes[subject] = rf.sseq
+				delete(asm.retmsgs, rf.subj)
+				asm.sl.Remove(rf.rmsg.sub)
+				deletes[rf.subj] = rf.rmsg.sseq
 			}
 		}
-		asm.mu.Unlock()
+
 		for subject, seq := range deletes {
 			asm.deleteRetainedMsg(seq)
 			asm.notifyRetainedMsgDeleted(subject, seq)