refactor of service overload logic

service/tier2.go

@@ -120,31 +120,47 @@ func NewTier2(
 	return s, nil
 }
 
+func (s *Tier2Service) isOverloaded() bool {
+	s.connectionCountMutex.RLock()
+	defer s.connectionCountMutex.RUnlock()
+	return s.runtimeConfig.MaxConcurrentRequests != 0 && s.currentConcurrentRequests >= s.runtimeConfig.MaxConcurrentRequests
+}
+
+func (s *Tier2Service) incrementConcurrentRequests() {
+	s.connectionCountMutex.Lock()
+	defer s.connectionCountMutex.Unlock()
+
+	s.currentConcurrentRequests++
+	s.setOverloaded()
+}
+
+func (s *Tier2Service) decrementConcurrentRequests() {
+	s.connectionCountMutex.Lock()
+	defer s.connectionCountMutex.Unlock()
+
+	s.currentConcurrentRequests--
+	s.setOverloaded()
+}
+
+func (s *Tier2Service) setOverloaded() {
+	overloaded := s.runtimeConfig.MaxConcurrentRequests != 0 && s.currentConcurrentRequests >= s.runtimeConfig.MaxConcurrentRequests
+	s.setReadyFunc(!overloaded)
+}
+
 func (s *Tier2Service) ProcessRange(request *pbssinternal.ProcessRangeRequest, streamSrv pbssinternal.Substreams_ProcessRangeServer) (grpcError error) {
 	// We keep `err` here as the unaltered error from `blocks` call, this is used in the EndSpan to record the full error
 	// and not only the `grpcError` one which is a subset view of the full `err`.
 	var err error
 	ctx := streamSrv.Context()
 
-	overloaded := true
-	s.connectionCountMutex.Lock()
-	if s.runtimeConfig.MaxConcurrentRequests == 0 || s.currentConcurrentRequests < s.runtimeConfig.MaxConcurrentRequests {
-		overloaded = false
-	}
-	if overloaded {
-		defer s.connectionCountMutex.Unlock()
-		return connect.NewError(connect.CodeUnavailable, fmt.Errorf("service overloaded"))
+	if s.isOverloaded() {
+		return connect.NewError(connect.CodeUnavailable, fmt.Errorf("service currently overloaded"))
 	}
 
-	s.currentConcurrentRequests++
-	s.setReadyFunc(s.runtimeConfig.MaxConcurrentRequests == 0 || s.currentConcurrentRequests <= s.runtimeConfig.MaxConcurrentRequests)
+	s.incrementConcurrentRequests()
 	defer func() {
-		s.connectionCountMutex.Lock()
-		s.currentConcurrentRequests--
-		s.setReadyFunc(s.runtimeConfig.MaxConcurrentRequests == 0 || s.currentConcurrentRequests < s.runtimeConfig.MaxConcurrentRequests)
-		s.connectionCountMutex.Unlock()
+		s.decrementConcurrentRequests()
 	}()
-	s.connectionCountMutex.Unlock()
 
 	// TODO: use stage and segment numbers when implemented
 	stage := request.OutputModule