Fixed dios capacity to 4 due to testing under heavy load.

Signed-off-by: Derek Collison <derek@nats.io>

server/filestore.go

@@ -6836,7 +6836,7 @@ var dios chan struct{}
 // golang.org's semaphore seemed a bit heavy.
 func init() {
 	// Based on Go max threads of 10k, limit ourselves to a max of 1k blocking IO calls.
-	const nIO = 1024
+	const nIO = 4
 	dios = make(chan struct{}, nIO)
 	// Fill it up to start.
 	for i := 0; i < nIO; i++ {

server/jetstream.go

@@ -853,9 +853,9 @@ func (s *Server) signalPullConsumers() {
 
 // Shutdown jetstream for this server.
 func (s *Server) shutdownJetStream() {
-	s.mu.Lock()
+	s.mu.RLock()
 	js := s.js
-	s.mu.Unlock()
+	s.mu.RUnlock()
 
 	if js == nil {
 		return