NEW FEATURE: Gather data for providers concurrently (#2873)

commands/zonecache.go

@@ -0,0 +1,27 @@
+package commands
+
+import "github.com/StackExchange/dnscontrol/v4/providers"
+
+func NewZoneCache() *zoneCache {
+	return &zoneCache{}
+}
+
+func (zc *zoneCache) zoneList(name string, lister providers.ZoneLister) (*[]string, error) {
+	zc.Lock()
+	defer zc.Unlock()
+
+	if zc.cache == nil {
+		zc.cache = map[string]*[]string{}
+	}
+
+	if v, ok := zc.cache[name]; ok {
+		return v, nil
+	}
+
+	zones, err := lister.ListZones()
+	if err != nil {
+		return nil, err
+	}
+	zc.cache[name] = &zones
+	return &zones, nil
+}