in flink-connector-gcp-pubsub/src/main/java/org/apache/flink/streaming/connectors/gcp/pubsub/PubSubSource.java [221:224]
public void restoreState(List<AcknowledgeIdsForCheckpoint<String>> state) throws Exception {
createAndSetPubSubSubscriber();
acknowledgeOnCheckpoint.restoreState(state);
}