package registry import ( "encoding/json" "errors" "sync" "go.etcd.io/bbolt" ) type ObjSelector struct { boltDB *bbolt.DB mu sync.Mutex lastId uint64 objStatus string } func (o *ObjSelector) NextObject() (*ObjectInfo, error) { var foundObj *ObjectInfo err := o.boltDB.View(func(tx *bbolt.Tx) error { b := tx.Bucket([]byte(bucketName)) if b == nil { return nil } c := b.Cursor() // We use mutex so that multiple VUs won't attempt to modify lastId simultaneously // TODO: consider singleton channel that will produce those ids on demand o.mu.Lock() defer o.mu.Unlock() // Establish the start position for searching the next object: // If we should go from the beginning (lastId=0), then we start from the first element // Otherwise we start from the key right after the lastId var keyBytes, objBytes []byte if o.lastId == 0 { keyBytes, objBytes = c.First() } else { c.Seek(encodeId(o.lastId)) keyBytes, objBytes = c.Next() } // Iterate over objects to find the next object in the target status var obj ObjectInfo for ; keyBytes != nil; keyBytes, objBytes = c.Next() { if objBytes != nil { if err := json.Unmarshal(objBytes, &obj); err != nil { // Ignore malformed objects for now. Maybe it should be panic? continue } // If we reached an object in the target status, stop iterating if obj.Status == o.objStatus { foundObj = &obj break } } } // Update the last key if keyBytes != nil { o.lastId = decodeId(keyBytes) return nil } return errors.New("no objects are available") }) return foundObj, err }