[GitHub] [rocketmq-clients] aaron-ai commented on a diff in pull request #342: Add API of PullConsumer

["aaron-ai (via GitHub)" <gi...@apache.org>]

aaron-ai commented on code in PR #342:
URL: https://github.com/apache/rocketmq-clients/pull/342#discussion_r1126501585


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java/client-apis/src/main/java/org/apache/rocketmq/client/apis/consumer/PullConsumer.java:
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@@ -0,0 +1,136 @@
+/*
+ * 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.rocketmq.client.apis.consumer;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.time.Duration;
+import java.util.Collection;
+import java.util.List;
+import java.util.Optional;
+import org.apache.rocketmq.client.apis.ClientException;
+import org.apache.rocketmq.client.apis.message.MessageQueue;
+import org.apache.rocketmq.client.apis.message.MessageView;
+
+public interface PullConsumer extends Closeable {
+    /**
+     * Get the consumer group of the consumer.
+     */
+    String getConsumerGroup();
+
+    /**
+     * @param topic    the topic that needs to be monitored.
+     * @param listener the callback to detect the message queue changes.
+     */
+    void registerMessageQueueChangeListenerByTopic(String topic, TopicMessageQueueChangeListener listener);
+
+    /**
+     * Fetch message queues of the topic.
+     */
+    Collection<MessageQueue> fetchMessageQueues(String topic) throws ClientException;
+
+    /**
+     * Manually assign a list of message queues to this consumer.
+     *
+     * <p>This interface does not allow for incremental assignment and will replace the previous assignment (if
+     * previous assignment existed).
+     *
+     * @param messageQueues the list of message queues that are to be assigned to this consumer.
+     */
+    void assign(Collection<MessageQueue> messageQueues);
+
+    /**
+     * Fetch messages from assigned message queues specified by {@link #assign(Collection)}.
+     *
+     * <p>The messages polled from remote are across the message queue.
+     *
+     * @param timeout the maximum time to block.
+     * @return list of fetched messages.
+     */
+    List<MessageView> poll(Duration timeout);

Review Comment:
   Should we also provide an asynchronous interface for PullConsumer#poll? If we only offer a synchronous interface, it means that each call will occupy one user thread. Typically, the poll interface is called for multiple queues, so occupying one thread may not have a significant impact. However, an asynchronous interface can provide greater flexibility, such as forming a future chain with the user's own methods, reducing unnecessary threads when multiple clients exist in one process, and potentially offering other benefits.
   
   We welcome everyone to join the discussion.



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