1 files changed, 38 insertions, 0 deletions
diff --git a/internal/mutex.go b/internal/mutex.go
new file mode 100644
index 00000000..3d36cdac
--- /dev/null
+++ b/internal/mutex.go
@@ -0,0 +1,38 @@
+package internal
+
+import "sync"
+
+type MutexByRoom struct {
+	mu       *sync.Mutex // protects the map
+	roomToMu map[string]*sync.Mutex
+}
+
+func NewMutexByRoom() *MutexByRoom {
+	return &MutexByRoom{
+		mu:       &sync.Mutex{},
+		roomToMu: make(map[string]*sync.Mutex),
+	}
+}
+
+func (m *MutexByRoom) Lock(roomID string) {
+	m.mu.Lock()
+	roomMu := m.roomToMu[roomID]
+	if roomMu == nil {
+		roomMu = &sync.Mutex{}
+	}
+	m.roomToMu[roomID] = roomMu
+	m.mu.Unlock()
+	// don't lock inside m.mu else we can deadlock
+	roomMu.Lock()
+}
+
+func (m *MutexByRoom) Unlock(roomID string) {
+	m.mu.Lock()
+	roomMu := m.roomToMu[roomID]
+	if roomMu == nil {
+		panic("MutexByRoom: Unlock before Lock")
+	}
+	m.mu.Unlock()
+
+	roomMu.Unlock()
+}