syhily commented on a change in pull request #17452:
URL: https://github.com/apache/flink/pull/17452#discussion_r794656612



##########
File path: 
flink-connectors/flink-connector-pulsar/src/main/java/org/apache/flink/connector/pulsar/sink/writer/topic/TopicMetadataListener.java
##########
@@ -0,0 +1,172 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+package org.apache.flink.connector.pulsar.sink.writer.topic;
+
+import org.apache.flink.annotation.Internal;
+import org.apache.flink.api.connector.sink.Sink.ProcessingTimeService;
+import org.apache.flink.connector.pulsar.sink.config.SinkConfiguration;
+
+import org.apache.flink.shaded.guava30.com.google.common.base.Objects;
+import org.apache.flink.shaded.guava30.com.google.common.collect.ImmutableList;
+
+import org.apache.pulsar.client.admin.PulsarAdmin;
+import org.apache.pulsar.client.admin.PulsarAdminException;
+import org.apache.pulsar.common.partition.PartitionedTopicMetadata;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static java.util.Collections.emptyList;
+import static 
org.apache.flink.connector.pulsar.common.config.PulsarConfigUtils.createAdmin;
+import static 
org.apache.flink.connector.pulsar.common.utils.PulsarExceptionUtils.sneakyAdmin;
+import static 
org.apache.flink.connector.pulsar.source.enumerator.topic.TopicNameUtils.isPartitioned;
+import static 
org.apache.flink.connector.pulsar.source.enumerator.topic.TopicNameUtils.topicNameWithPartition;
+
+/**
+ * We need the latest topic metadata for making sure the newly created topic 
partitions would be
+ * used by Pulsar sink. This routing policy would be different comparing with 
Pulsar Client built-in
+ * logic. We use flink's ProcessingTimer as the executor.
+ */
+@Internal
+public class TopicMetadataListener implements Serializable, Closeable {
+    private static final long serialVersionUID = 6186948471557507522L;
+
+    private static final Logger LOG = 
LoggerFactory.getLogger(TopicMetadataListener.class);
+
+    private final List<String> partitionedTopics;
+    private final Map<String, Integer> topicMetadata;
+    private volatile ImmutableList<String> availableTopics;
+
+    // Dynamic fields.
+    private transient PulsarAdmin pulsarAdmin;
+    private transient Long topicMetadataRefreshInterval;
+    private transient ProcessingTimeService timeService;
+
+    public TopicMetadataListener() {
+        this(emptyList());
+    }
+
+    public TopicMetadataListener(List<String> topics) {
+        this.partitionedTopics = new ArrayList<>(topics.size());
+        this.topicMetadata = new HashMap<>(topics.size());
+        this.availableTopics = ImmutableList.of();
+
+        for (String topic : topics) {
+            if (isPartitioned(topic)) {
+                partitionedTopics.add(topic);
+            } else {
+                // This would be updated when open writing.
+                topicMetadata.put(topic, -1);
+            }
+        }
+    }
+
+    /** Register the topic metadata update in process time service. */
+    public void open(SinkConfiguration sinkConfiguration, 
ProcessingTimeService timeService) {
+        if (topicMetadata.isEmpty()) {
+            LOG.info("No topics have been provided, skip listener 
initialize.");
+            return;
+        }
+
+        // Initialize listener properties.
+        this.pulsarAdmin = createAdmin(sinkConfiguration);
+        this.topicMetadataRefreshInterval = 
sinkConfiguration.getTopicMetadataRefreshInterval();
+        this.timeService = timeService;
+
+        // Initialize the topic metadata. Quit if fail to connect to Pulsar.
+        sneakyAdmin(this::updateTopicMetadata);
+
+        // Register time service.
+        triggerNextTopicMetadataUpdate(true);
+    }
+
+    /**
+     * Return all the available topic partitions. We would recalculate the 
partitions if the topic
+     * metadata hsa been changed. Otherwise, we would return the cached result 
for better
+     * performance.
+     */
+    public List<String> availableTopics() {
+        if (availableTopics.isEmpty()
+                && (!partitionedTopics.isEmpty() || !topicMetadata.isEmpty())) 
{

Review comment:
       I should point out your mistake. We only evaluate the `availableTopics` 
when it needs updating. This is a cached result, which should be created every 
time we call this method.
   
   Putting the evaluate logic here is just a design flavor. XD




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