cmd/xk6-registry-exporter/root.go

@@ -78,7 +78,7 @@ func rootCmdRun(cmd *cobra.Command, args []string) error {
 	}
 
 	objRegistry := registry.NewObjRegistry(cmd.Context(), args[0])
-	objSelector := registry.NewObjSelector(objRegistry, 0, false, &registry.ObjFilter{
+	objSelector := registry.NewObjSelector(objRegistry, 0, registry.SelectorAwaiting, &registry.ObjFilter{
 		Status: status,
 		Age:    age,
 	})

internal/registry/obj_selector.go

@@ -20,7 +20,7 @@ type ObjSelector struct {
 	boltDB    *bbolt.DB
 	filter    *ObjFilter
 	cacheSize int
-	looped    bool
+	kind      SelectorKind
 }
 
 // objectSelectCache is the default maximum size of a batch to select from DB.
@@ -28,7 +28,7 @@ const objectSelectCache = 1000
 
 // NewObjSelector creates a new instance of object selector that can iterate over
 // objects in the specified registry.
-func NewObjSelector(registry *ObjRegistry, selectionSize int, looped bool, filter *ObjFilter) *ObjSelector {
+func NewObjSelector(registry *ObjRegistry, selectionSize int, kind SelectorKind, filter *ObjFilter) *ObjSelector {
 	if selectionSize <= 0 {
 		selectionSize = objectSelectCache
 	}
@@ -41,7 +41,7 @@ func NewObjSelector(registry *ObjRegistry, selectionSize int, looped bool, filte
 		filter:    filter,
 		objChan:   make(chan *ObjectInfo, selectionSize*2),
 		cacheSize: selectionSize,
-		looped:    looped,
+		kind:      kind,
 	}
 
 	go objSelector.selectLoop()
@@ -162,7 +162,11 @@ func (o *ObjSelector) selectLoop() {
 			}
 		}
 
-		if !o.looped && len(cache) != o.cacheSize {
+		if o.kind == SelectorOneshot && len(cache) != o.cacheSize {
+			return
+		}
+
+		if o.kind != SelectorLooped && len(cache) != o.cacheSize {
 			// no more objects, wait a little; the logic could be improved.
 			select {
 			case <-time.After(time.Second):
@@ -171,7 +175,7 @@ func (o *ObjSelector) selectLoop() {
 			}
 		}
 
-		if o.looped && len(cache) != o.cacheSize {
+		if o.kind == SelectorLooped && len(cache) != o.cacheSize {
 			lastID = 0
 		}
 

internal/registry/registry.go

@@ -74,15 +74,35 @@ func (r *Registry) open(dbFilePath string) *ObjRegistry {
 	return registry
 }
 
+// SelectorKind represents selector behaviour when no items are available.
+type SelectorKind byte
+
+const (
+	// SelectorAwaiting waits for a new item to arrive.
+	// This selector visits each item exactly once and can be used when items
+	// to select are being pushed into registry concurrently.
+	SelectorAwaiting = iota
+	// SelectorLooped rewinds cursor to the start after all items have been read.
+	// It can encounter duplicates and should be used mostly for read scenarious.
+	SelectorLooped
+	// SelectorOneshot visits each item exactly once and exits immediately afterwards.
+	// It may be used to artificially abort the test after all items were processed.
+	SelectorOneshot
+)
+
 func (r *Registry) GetSelector(dbFilePath string, name string, cacheSize int, filter map[string]string) *ObjSelector {
-	return r.getSelectorInternal(dbFilePath, name, cacheSize, false, filter)
+	return r.getSelectorInternal(dbFilePath, name, cacheSize, SelectorAwaiting, filter)
 }
 
 func (r *Registry) GetLoopedSelector(dbFilePath string, name string, cacheSize int, filter map[string]string) *ObjSelector {
-	return r.getSelectorInternal(dbFilePath, name, cacheSize, true, filter)
+	return r.getSelectorInternal(dbFilePath, name, cacheSize, SelectorLooped, filter)
 }
 
-func (r *Registry) getSelectorInternal(dbFilePath string, name string, cacheSize int, looped bool, filter map[string]string) *ObjSelector {
+func (r *Registry) GetOneshotSelector(dbFilePath string, name string, cacheSize int, filter map[string]string) *ObjSelector {
+	return r.getSelectorInternal(dbFilePath, name, cacheSize, SelectorOneshot, filter)
+}
+
+func (r *Registry) getSelectorInternal(dbFilePath string, name string, cacheSize int, kind SelectorKind, filter map[string]string) *ObjSelector {
 	objFilter, err := parseFilter(filter)
 	if err != nil {
 		panic(err)
@@ -94,7 +114,7 @@ func (r *Registry) getSelectorInternal(dbFilePath string, name string, cacheSize
 	selector := r.root.selectors[name]
 	if selector == nil {
 		registry := r.open(dbFilePath)
-		selector = NewObjSelector(registry, cacheSize, looped, objFilter)
+		selector = NewObjSelector(registry, cacheSize, kind, objFilter)
 		r.root.selectors[name] = selector
 	} else if !reflect.DeepEqual(selector.filter, objFilter) {
 		panic(fmt.Sprintf("selector %s already has been created with a different filter", name))