Stats: Fix GetOrRegister*() races (#6468)

Fixes https://github.com/XTLS/Xray-core/pull/6467#issue-4856851059

---------

Co-authored-by: Joshua Su <i@joshua.su>

app/stats/stats.go

@@ -48,6 +48,20 @@ func (m *Manager) RegisterCounter(name string) (stats.Counter, error) {
 	return c, nil
 }
 
+// GetOrRegisterCounter implements stats.Manager.
+func (m *Manager) GetOrRegisterCounter(name string) (stats.Counter, error) {
+	m.access.Lock()
+	defer m.access.Unlock()
+
+	if c, found := m.counters[name]; found {
+		return c, nil
+	}
+	errors.LogDebug(context.Background(), "create new counter ", name)
+	c := new(Counter)
+	m.counters[name] = c
+	return c, nil
+}
+
 // UnregisterCounter implements stats.Manager.
 func (m *Manager) UnregisterCounter(name string) error {
 	m.access.Lock()
@@ -97,6 +111,20 @@ func (m *Manager) RegisterOnlineMap(name string) (stats.OnlineMap, error) {
 	return om, nil
 }
 
+// GetOrRegisterOnlineMap implements stats.Manager.
+func (m *Manager) GetOrRegisterOnlineMap(name string) (stats.OnlineMap, error) {
+	m.access.Lock()
+	defer m.access.Unlock()
+
+	if om, found := m.onlineMaps[name]; found {
+		return om, nil
+	}
+	errors.LogDebug(context.Background(), "create new OnlineMap ", name)
+	om := NewOnlineMap()
+	m.onlineMaps[name] = om
+	return om, nil
+}
+
 // UnregisterOnlineMap implements stats.Manager.
 func (m *Manager) UnregisterOnlineMap(name string) error {
 	m.access.Lock()
@@ -149,6 +177,26 @@ func (m *Manager) RegisterChannel(name string) (stats.Channel, error) {
 	return c, nil
 }
 
+// GetOrRegisterChannel implements stats.Manager.
+func (m *Manager) GetOrRegisterChannel(name string) (stats.Channel, error) {
+	m.access.Lock()
+	defer m.access.Unlock()
+
+	if c, found := m.channels[name]; found {
+		return c, nil
+	}
+	errors.LogDebug(context.Background(), "create new channel ", name)
+	c := NewChannel(&ChannelConfig{BufferSize: 64, Blocking: false})
+	if m.running {
+		// Start before publishing so no goroutine can observe an unstarted channel.
+		if err := c.Start(); err != nil {
+			return nil, err
+		}
+	}
+	m.channels[name] = c
+	return c, nil
+}
+
 // UnregisterChannel implements stats.Manager.
 func (m *Manager) UnregisterChannel(name string) error {
 	m.access.Lock()