Add tags cache to app.proxyman.ohm.Select() (#2927)

* Add tags cache to ohm.Select().

* Refactor round-robin.

* Fix a bug.

---------

Co-authored-by: nobody <nobody@nowhere.mars>

app/proxyman/outbound/outbound.go

@@ -22,12 +22,14 @@ type Manager struct {
 	taggedHandler    map[string]outbound.Handler
 	untaggedHandlers []outbound.Handler
 	running          bool
+	tagsCache        map[string][]string
 }
 
 // New creates a new Manager.
 func New(ctx context.Context, config *proxyman.OutboundConfig) (*Manager, error) {
 	m := &Manager{
 		taggedHandler: make(map[string]outbound.Handler),
+		tagsCache:     make(map[string][]string),
 	}
 	return m, nil
 }
@@ -104,6 +106,8 @@ func (m *Manager) AddHandler(ctx context.Context, handler outbound.Handler) erro
 	m.access.Lock()
 	defer m.access.Unlock()
 
+	m.tagsCache = make(map[string][]string)
+
 	if m.defaultHandler == nil {
 		m.defaultHandler = handler
 	}
@@ -133,6 +137,8 @@ func (m *Manager) RemoveHandler(ctx context.Context, tag string) error {
 	m.access.Lock()
 	defer m.access.Unlock()
 
+	m.tagsCache = make(map[string][]string)
+
 	delete(m.taggedHandler, tag)
 	if m.defaultHandler != nil && m.defaultHandler.Tag() == tag {
 		m.defaultHandler = nil
@@ -146,6 +152,11 @@ func (m *Manager) Select(selectors []string) []string {
 	m.access.RLock()
 	defer m.access.RUnlock()
 
+	key := strings.Join(selectors, ",")
+	if cache, ok := m.tagsCache[key]; ok {
+		return cache
+	}
+
 	tags := make([]string, 0, len(selectors))
 
 	for tag := range m.taggedHandler {
@@ -156,7 +167,10 @@ func (m *Manager) Select(selectors []string) []string {
 			}
 		}
 	}
+
 	sort.Strings(tags)
+	m.tagsCache[key] = tags
+
 	return tags
 }