nsqlookupd: add lock pretection for cachedFindProducersResults

nsqlookupd/registration_db.go

@@ -13,6 +13,7 @@ type RegistrationDB struct {
 	sync.RWMutex
 	registrationMap map[Registration]ProducerMap
 
+	cachedMutex                sync.RWMutex
 	cachedFindProducersResults *cache.Cache
 }
 
@@ -184,15 +185,26 @@ func (r *RegistrationDB) FindRegistrations(category string, key string, subkey s
 }
 
 func (r *RegistrationDB) FindProducers(category string, key string, subkey string) Producers {
-	r.RLock()
-	defer r.RUnlock()
-
+	r.cachedMutex.RLock()
 	cachedKey := fmt.Sprintf("%s:%s:%s", category, key, subkey)
 
+	if val, found := r.cachedFindProducersResults.Get(cachedKey); found {
+		r.cachedMutex.Unlock()
+		return val.(Producers)
+	}
+
+	r.cachedMutex.Unlock()
+
+	r.cachedMutex.Lock()
+	defer r.cachedMutex.Unlock()
+
 	if val, found := r.cachedFindProducersResults.Get(cachedKey); found {
 		return val.(Producers)
 	}
 
+	r.RLock()
+	defer r.RUnlock()
+
 	if !r.needFilter(key, subkey) {
 		k := Registration{category, key, subkey}
 		r.cachedFindProducersResults.Set(cachedKey, ProducerMap2Slice(r.registrationMap[k]), cache.DefaultExpiration)