First Commit of Voltha-Go-Controller from Radisys

Change-Id: I8e2e908e7ab09a4fe3d86849da18b6d69dcf4ab0
diff --git a/internal/pkg/holder/doc.go b/internal/pkg/holder/doc.go
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+++ b/internal/pkg/holder/doc.go
@@ -0,0 +1,32 @@
+/*
+ *   Copyright 2020-present Open Networking Foundation
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+// The implementation of the open flow agent (vpagent) uses a GRPC connection
+// to VOLTHA accross several implementaton packages including the vpagent and
+// openflow packages. This GRPC connection is shared through packages and type
+// instances via injection.
+//
+// As the vpagent executes within a micro-service environment it is
+// possible that the GRPC connection is reset (re-established). When the connection
+// is re-established, because injection is used, the new value needs to be
+// re-injected across the implementation.
+//
+// To help simply the re-injection or value change scenario a holder for the
+// GRPC connection is established so that the reference to the holder can
+// stay [sic] consistant over the lifetime of the vpagent while the underlying
+// GRPC connection can change without walking the entire runtime structure.
+
+package holder