diff --git a/hub.go b/hub.go
index 4a8cffa..a3b2977 100644
--- a/hub.go
+++ b/hub.go
@@ -2,90 +2,124 @@ package melody
 
 import (
 	"sync"
+	"sync/atomic"
 )
 
+type sessionSet struct {
+	mu      sync.RWMutex
+	members map[*Session]struct{}
+}
+
+func (ss *sessionSet) add(s *Session) {
+	ss.mu.Lock()
+	defer ss.mu.Unlock()
+
+	ss.members[s] = struct{}{}
+}
+
+func (ss *sessionSet) del(s *Session) {
+	ss.mu.Lock()
+	defer ss.mu.Unlock()
+
+	delete(ss.members, s)
+}
+
+func (ss *sessionSet) clear() {
+	ss.mu.Lock()
+	defer ss.mu.Unlock()
+
+	ss.members = make(map[*Session]struct{})
+}
+
+func (ss *sessionSet) each(cb func(*Session)) {
+	ss.mu.RLock()
+	defer ss.mu.RUnlock()
+
+	for s := range ss.members {
+		cb(s)
+	}
+}
+
+func (ss *sessionSet) len() int {
+	ss.mu.RLock()
+	defer ss.mu.RUnlock()
+
+	return len(ss.members)
+}
+
+func (ss *sessionSet) all() []*Session {
+	ss.mu.RLock()
+	defer ss.mu.RUnlock()
+
+	s := make([]*Session, 0, len(ss.members))
+	for k := range ss.members {
+		s = append(s, k)
+	}
+
+	return s
+}
+
 type hub struct {
-	sessions   map[*Session]bool
+	sessions   sessionSet
 	broadcast  chan *envelope
 	register   chan *Session
 	unregister chan *Session
 	exit       chan *envelope
-	open       bool
-	rwmutex    *sync.RWMutex
+	open       atomic.Bool
 }
 
 func newHub() *hub {
 	return &hub{
-		sessions:   make(map[*Session]bool),
+		sessions: sessionSet{
+			members: make(map[*Session]struct{}),
+		},
 		broadcast:  make(chan *envelope),
 		register:   make(chan *Session),
 		unregister: make(chan *Session),
 		exit:       make(chan *envelope),
-		open:       true,
-		rwmutex:    &sync.RWMutex{},
 	}
 }
 
 func (h *hub) run() {
+	h.open.Store(true)
+
 loop:
 	for {
 		select {
 		case s := <-h.register:
-			h.rwmutex.Lock()
-			h.sessions[s] = true
-			h.rwmutex.Unlock()
+			h.sessions.add(s)
 		case s := <-h.unregister:
-			if _, ok := h.sessions[s]; ok {
-				h.rwmutex.Lock()
-				delete(h.sessions, s)
-				h.rwmutex.Unlock()
-			}
+			h.sessions.del(s)
 		case m := <-h.broadcast:
-			h.rwmutex.RLock()
-			for s := range h.sessions {
-				if m.filter != nil {
-					if m.filter(s) {
-						s.writeMessage(m)
-					}
-				} else {
+			h.sessions.each(func(s *Session) {
+				if m.filter == nil {
+					s.writeMessage(m)
+				} else if m.filter(s) {
 					s.writeMessage(m)
 				}
-			}
-			h.rwmutex.RUnlock()
+			})
 		case m := <-h.exit:
-			h.rwmutex.Lock()
-			for s := range h.sessions {
+			h.sessions.each(func(s *Session) {
 				s.writeMessage(m)
-				delete(h.sessions, s)
 				s.Close()
-			}
-			h.open = false
-			h.rwmutex.Unlock()
+			})
+
+			h.sessions.clear()
+			h.open.Store(false)
+
 			break loop
 		}
 	}
 }
 
 func (h *hub) closed() bool {
-	h.rwmutex.RLock()
-	defer h.rwmutex.RUnlock()
-	return !h.open
+	return !h.open.Load()
 }
 
 func (h *hub) len() int {
-	h.rwmutex.RLock()
-	defer h.rwmutex.RUnlock()
-
-	return len(h.sessions)
+	return h.sessions.len()
 }
 
 func (h *hub) all() []*Session {
-	h.rwmutex.RLock()
-	defer h.rwmutex.RUnlock()
-
-	s := make([]*Session, 0, len(h.sessions))
-	for k := range h.sessions {
-		s = append(s, k)
-	}
-	return s
+	return h.sessions.all()
 }