in flink-connector-gcp-pubsub/src/main/java/org/apache/flink/streaming/connectors/gcp/pubsub/PubSubSource.java [226:233]
private void createAndSetPubSubSubscriber() throws Exception {
if (subscriber == null) {
this.subscriber = pubSubSubscriberFactory.getSubscriber(credentials);
}
if (acknowledgeOnCheckpoint == null) {
this.acknowledgeOnCheckpoint = acknowledgeOnCheckpointFactory.create(subscriber);
}
}