[GitHub] [pulsar] dao-jun commented on a diff in pull request #19641: [feat][txn] Transaction buffer snapshot writer reuse

["dao-jun (via GitHub)" <gi...@apache.org>]

dao-jun commented on code in PR #19641:
URL: https://github.com/apache/pulsar/pull/19641#discussion_r1118850555


##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/service/SystemTopicTxnBufferSnapshotService.java:
##########
@@ -18,66 +18,154 @@
  */
 package org.apache.pulsar.broker.service;
 
+import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicLong;
+import lombok.extern.slf4j.Slf4j;
 import org.apache.pulsar.broker.systopic.NamespaceEventsSystemTopicFactory;
 import org.apache.pulsar.broker.systopic.SystemTopicClient;
 import org.apache.pulsar.broker.systopic.SystemTopicClientBase;
 import org.apache.pulsar.client.api.PulsarClient;
 import org.apache.pulsar.client.api.PulsarClientException;
 import org.apache.pulsar.common.events.EventType;
+import org.apache.pulsar.common.naming.NamespaceName;
 import org.apache.pulsar.common.naming.TopicName;
-import org.apache.pulsar.common.util.FutureUtil;
 
+@Slf4j
 public class SystemTopicTxnBufferSnapshotService<T> {
 
-    protected final Map<TopicName, SystemTopicClient<T>> clients;
+    protected final ConcurrentHashMap<NamespaceName, SystemTopicClient<T>> clients;
     protected final NamespaceEventsSystemTopicFactory namespaceEventsSystemTopicFactory;
 
     protected final Class<T> schemaType;
     protected final EventType systemTopicType;
 
+    private final HashMap<NamespaceName, ReferenceCountedWriter<T>> refCountedWriterMap;
+
+    // The class ReferenceCountedWriter will maintain the reference count,
+    // when the reference count decrement to 0, it will be removed from writerFutureMap, the writer will be closed.
+    public static class ReferenceCountedWriter<T> {
+
+        private final AtomicLong referenceCount;
+        private final NamespaceName namespaceName;
+        private final CompletableFuture<SystemTopicClient.Writer<T>> future;
+        private final SystemTopicTxnBufferSnapshotService<T> snapshotService;
+
+        public ReferenceCountedWriter(NamespaceName namespaceName,
+                                      CompletableFuture<SystemTopicClient.Writer<T>> future,
+                                      SystemTopicTxnBufferSnapshotService<T> snapshotService) {
+            this.referenceCount = new AtomicLong(1);
+            this.namespaceName = namespaceName;
+            this.snapshotService = snapshotService;
+            this.future = future;
+            this.future.exceptionally(t -> {
+                        log.error("[{}] Failed to create transaction buffer snapshot writer.", namespaceName, t);
+                snapshotService.refCountedWriterMap.remove(namespaceName, this);
+                return null;
+            });
+        }
+
+        public CompletableFuture<SystemTopicClient.Writer<T>> getFuture() {
+            return future;
+        }
+
+        private void retain() {
+            operationValidate(true);
+            this.referenceCount.incrementAndGet();
+        }
+
+        private long release() {
+            operationValidate(false);
+            return this.referenceCount.decrementAndGet();
+        }
+
+        private void operationValidate(boolean isRetain) {
+            if (this.referenceCount.get() == 0) {
+                throw new RuntimeException(
+                        "[" + namespaceName + "] The reference counted transaction buffer snapshot writer couldn't "
+                                + "be " + (isRetain ? "retained" : "released") + ", refCnt is 0.");
+            }
+        }
+
+        public void close() {
+            if (release() == 0) {
+                snapshotService.refCountedWriterMap.remove(namespaceName, this);
+                future.thenAccept(writer -> {
+                    final String topicName = writer.getSystemTopicClient().getTopicName().toString();
+                    writer.closeAsync().exceptionally(t -> {
+                        if (t != null) {
+                            log.error("[{}] Failed to close writer.", topicName, t);
+                        } else {
+                            if (log.isDebugEnabled()) {
+                                log.debug("[{}] Success to close writer.", topicName);
+                            }
+                        }
+                        return null;
+                    });
+                });
+            }
+        }
+
+    }
+
     public SystemTopicTxnBufferSnapshotService(PulsarClient client, EventType systemTopicType,
                                                Class<T> schemaType) {
         this.namespaceEventsSystemTopicFactory = new NamespaceEventsSystemTopicFactory(client);
         this.systemTopicType = systemTopicType;
         this.schemaType = schemaType;
         this.clients = new ConcurrentHashMap<>();
+        this.refCountedWriterMap = new HashMap<>();

Review Comment:
   Maybe it's better to use ConcurrentHashMap?



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