Add read-write lock to guard topology changes on new collections and ttls.

go/util/concurrent_read_map.go

@@ -0,0 +1,37 @@
+package util
+
+import "sync"
+
+// A mostly for read map, which can thread-safely
+// initialize the map entries.
+type ConcurrentReadMap struct {
+	rmutex sync.RWMutex
+	mutex  sync.Mutex
+	Items  map[string]interface{}
+}
+
+func NewConcurrentReadMap() *ConcurrentReadMap {
+	return &ConcurrentReadMap{Items: make(map[string]interface{})}
+}
+
+func (m *ConcurrentReadMap) initMapEntry(key string, newEntry func() interface{}) (value interface{}) {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+	if value, ok := m.Items[key]; ok {
+		return value
+	}
+	value = newEntry()
+	m.Items[key] = value
+	return value
+}
+
+func (m *ConcurrentReadMap) Get(key string, newEntry func() interface{}) interface{} {
+	m.rmutex.RLock()
+	if value, ok := m.Items[key]; ok {
+		m.rmutex.RUnlock()
+		return value
+	} else {
+		m.rmutex.RUnlock()
+		return m.initMapEntry(key, newEntry)
+	}
+}