Denovo1998 commented on code in PR #24833:
URL: https://github.com/apache/pulsar/pull/24833#discussion_r2432187651


##########
pulsar-common/src/main/java/org/apache/pulsar/common/semaphore/AsyncSemaphoreImpl.java:
##########
@@ -0,0 +1,286 @@
+/*
+ * 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.pulsar.common.semaphore;
+
+import io.netty.util.concurrent.DefaultThreadFactory;
+import java.util.Queue;
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicLongFieldUpdater;
+import java.util.function.BooleanSupplier;
+import java.util.function.LongConsumer;
+import org.apache.pulsar.common.util.Runnables;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Implementation of AsyncSemaphore with timeout and queue size limits.
+ */
+public class AsyncSemaphoreImpl implements AsyncSemaphore, AutoCloseable {
+    private static final Logger log = 
LoggerFactory.getLogger(AsyncSemaphoreImpl.class);
+
+    private final AtomicLong availablePermits;
+    private final Queue<PendingRequest> queue;
+    private final long maxPermits;
+    private final long timeoutMillis;
+    private final ScheduledExecutorService executor;
+    private final boolean shutdownExecutor;
+    private final LongConsumer queueLatencyRecorder;
+    private final AtomicBoolean closed = new AtomicBoolean(false);
+    private final Runnable processQueueRunnable = 
Runnables.catchingAndLoggingThrowables(this::internalProcessQueue);
+
+    public AsyncSemaphoreImpl(long maxPermits, int maxQueueSize, long 
timeoutMillis) {
+        this(maxPermits, maxQueueSize, timeoutMillis, createExecutor(), true, 
null);
+    }
+
+    public AsyncSemaphoreImpl(long maxPermits, int maxQueueSize, long 
timeoutMillis,
+                              ScheduledExecutorService executor, LongConsumer 
queueLatencyRecorder) {
+        this(maxPermits, maxQueueSize, timeoutMillis, executor, false, 
queueLatencyRecorder);
+    }
+
+    AsyncSemaphoreImpl(long maxPermits, int maxQueueSize, long timeoutMillis, 
ScheduledExecutorService executor,
+                       boolean shutdownExecutor, LongConsumer 
queueLatencyRecorder) {
+        this.availablePermits = new AtomicLong(maxPermits);
+        this.maxPermits = maxPermits;
+        this.queue = new ArrayBlockingQueue<>(maxQueueSize);
+        this.timeoutMillis = timeoutMillis;
+        this.executor = executor;
+        this.shutdownExecutor = shutdownExecutor;
+        this.queueLatencyRecorder = queueLatencyRecorder;
+    }
+
+    private static ScheduledExecutorService createExecutor() {
+        return Executors.newSingleThreadScheduledExecutor(
+                new DefaultThreadFactory("async-semaphore-executor"));
+    }
+
+    @Override
+    public CompletableFuture<AsyncSemaphorePermit> acquire(long permits, 
BooleanSupplier isCancelled) {
+        return internalAcquire(permits, permits, isCancelled);
+    }
+
+    private CompletableFuture<AsyncSemaphorePermit> internalAcquire(long 
permits, long acquirePermits,
+                                                                    
BooleanSupplier isCancelled) {
+        if (permits < 0) {
+            throw new IllegalArgumentException("Invalid permits value: " + 
permits);
+        }
+
+        CompletableFuture<AsyncSemaphorePermit> future = new 
CompletableFuture<>();
+
+        if (closed.get()) {
+            future.completeExceptionally(new 
PermitAcquireAlreadyClosedException("Semaphore is closed"));
+            return future;
+        }
+
+        PendingRequest request = new PendingRequest(permits, acquirePermits, 
future, isCancelled);
+        if (!queue.offer(request)) {
+            future.completeExceptionally(new PermitAcquireQueueFullException(
+                    "Semaphore queue is full"));
+            return future;
+        }
+        // Schedule timeout
+        ScheduledFuture<?> timeoutTask = executor.schedule(() -> {
+            if (!request.future.isDone() && queue.remove(request)) {
+                // timeout is recorded with Long.MAX_VALUE as the age
+                recordQueueLatency(Long.MAX_VALUE);
+                // also record the time in the queue
+                recordQueueLatency(request.getAgeNanos());
+                future.completeExceptionally(new PermitAcquireTimeoutException(
+                        "Permit acquisition timed out"));
+                // the next request might have smaller permits and that might 
be processed
+                processQueue();
+            }
+        }, timeoutMillis, TimeUnit.MILLISECONDS);
+        request.setTimeoutTask(timeoutTask);
+
+        processQueue();
+        return future;
+    }
+
+    private void recordQueueLatency(long ageNanos) {
+        if (queueLatencyRecorder != null) {
+            queueLatencyRecorder.accept(ageNanos);
+        }
+    }
+
+    @Override
+    public CompletableFuture<AsyncSemaphorePermit> update(AsyncSemaphorePermit 
permit, long newPermits,
+                                                          BooleanSupplier 
isCancelled) {
+        if (newPermits < 0) {
+            throw new IllegalArgumentException("Invalid permits value: " + 
newPermits);
+        }
+        long oldPermits = permit.getPermits();
+        long additionalPermits = newPermits - oldPermits;
+        // mark the old permits as released without adding the permits to 
availablePermits
+        castToImplementation(permit).releasePermits();
+        if (additionalPermits > 0) {
+            return internalAcquire(newPermits, additionalPermits, isCancelled);
+        } else {
+            // new permits are less than the old ones, so we return the 
difference
+            availablePermits.addAndGet(-additionalPermits);
+            processQueue();
+            // return the new permits immediately
+            return CompletableFuture.completedFuture(new 
SemaphorePermit(newPermits));
+        }
+    }
+
+    @Override
+    public void release(AsyncSemaphorePermit permit) {
+        
availablePermits.addAndGet(castToImplementation(permit).releasePermits());
+        processQueue();
+    }
+
+    @Override
+    public long getAvailablePermits() {
+        return availablePermits.get();
+    }
+
+    @Override
+    public long getAcquiredPermits() {
+        return maxPermits - availablePermits.get();
+    }
+
+    @Override
+    public int getQueueSize() {
+        return queue.size();
+    }
+
+    private SemaphorePermit castToImplementation(AsyncSemaphorePermit permit) {
+        if (permit instanceof SemaphorePermit semaphorePermit) {
+            return semaphorePermit;
+        } else {
+            throw new IllegalArgumentException("Invalid permit type");
+        }
+    }
+
+    private void processQueue() {
+        if (closed.get()) {
+            return;
+        }
+        executor.execute(processQueueRunnable);
+    }
+
+    private void internalProcessQueue() {

Review Comment:
   Is there a race condition here?
   - Line 187: current = 10
   - Request needs 8 permits
   - Another thread calls update(), reducing availablePermits to 3
   - Line 205: Check passes (8 <= 10 using stale current)
   - Line 206: availablePermits = 3 - 8 = -5 (negative!)
   This violates the semaphore invariant, allowing more permits to be acquired 
than maxPermits.



##########
pip/pip-442.md:
##########
@@ -163,227 +189,409 @@ public interface AsyncDualMemoryLimiter {
         HEAP_MEMORY,    // For heap memory allocation
         DIRECT_MEMORY   // For direct memory allocation
     }
-    
+
     /**
      * Acquire permits for the specified memory size.
      * Returned future completes when memory permits are available.
-     * It will complete exceptionally with 
AsyncSemaphorePermitAcquireTimeoutException on timeout
-     * and exceptionally with AsyncSemaphorePermitAcquireQueueFullException 
when queue full
+     * It will complete exceptionally with 
AsyncSemaphore.PermitAcquireTimeoutException on timeout
+     * and exceptionally with AsyncSemaphore.PermitAcquireQueueFullException 
when queue full
+     *
+     * @param memorySize  the size of memory to acquire permits for
+     * @param limitType   the type of memory limit (HEAP_MEMORY or 
DIRECT_MEMORY)
+     * @param isCancelled supplier that returns true if acquisition should be 
cancelled
      * @return CompletableFuture that completes with permit when available
      */
-    CompletableFuture<AsyncDualMemoryLimiterPermit> acquire(long memorySize, 
LimitType limitType);
+    CompletableFuture<AsyncDualMemoryLimiterPermit> acquire(long memorySize, 
LimitType limitType,
+                                                            BooleanSupplier 
isCancelled);
 
     /**
      * Acquire or release permits for previously acquired permits by updating 
the requested memory size.
      * Returns a future that completes when permits are available.
-     * It will complete exceptionally with 
AsyncSemaphorePermitAcquireTimeoutException on timeout
-     * and exceptionally with AsyncSemaphorePermitAcquireQueueFullException 
when queue full
+     * It will complete exceptionally with 
AsyncSemaphore.PermitAcquireTimeoutException on timeout
+     * and exceptionally with AsyncSemaphore.PermitAcquireQueueFullException 
when queue full
+     * The provided permit is released when the permits are successfully 
acquired and the returned updated
+     * permit replaces the old instance.
+     *
+     * @param permit        the previously acquired permit to update
+     * @param newMemorySize the new memory size to update to
+     * @param isCancelled   supplier that returns true if update should be 
cancelled
      * @return CompletableFuture that completes with permit when available
      */
-    CompletableFuture<AsyncDualMemoryLimiterPermit> 
update(AsyncDualMemoryLimiterPermit permit, long newMemorySize);
-    
+    CompletableFuture<AsyncDualMemoryLimiterPermit> 
update(AsyncDualMemoryLimiterPermit permit, long newMemorySize,
+                                                           BooleanSupplier 
isCancelled);
+
     /**
      * Release previously acquired permit.
      * Must be called to prevent memory permit leaks.
+     *
+     * @param permit the permit to release
      */
     void release(AsyncDualMemoryLimiterPermit permit);
+    /**
+     * Execute the specified function with acquired permits and release the 
permits after the returned future completes.
+     * @param memorySize memory size to acquire permits for
+     * @param limitType memory limit type to acquire permits for
+     * @param function function to execute with acquired permits
+     * @return result of the function
+     * @param <T> type of the CompletableFuture returned by the function
+     */
+    default <T> CompletableFuture<T> withAcquiredPermits(long memorySize, 
LimitType limitType,
+                                                         BooleanSupplier 
isCancelled,
+                                                         
Function<AsyncDualMemoryLimiterPermit,
+                                                                 
CompletableFuture<T>> function,
+                                                         Function<Throwable, 
CompletableFuture<T>>
+                                                                 
permitAcquireErrorHandler) {
+        return 
AsyncDualMemoryLimiterUtil.withPermitsFuture(acquire(memorySize, limitType, 
isCancelled), function,
+                permitAcquireErrorHandler, this::release);
+    }
+
+    /**
+     * Executed the specified function with updated permits and release the 
permits after the returned future completes.
+     * @param initialPermit initial permit to update
+     * @param newMemorySize new memory size to update to
+     * @param function function to execute with updated permits
+     * @return result of the function
+     * @param <T> type of the CompletableFuture returned by the function
+     */
+    default <T> CompletableFuture<T> 
withUpdatedPermits(AsyncDualMemoryLimiterPermit initialPermit, long 
newMemorySize,
+                                                        BooleanSupplier 
isCancelled,
+                                                        
Function<AsyncDualMemoryLimiterPermit,
+                                                                
CompletableFuture<T>> function,
+                                                        Function<Throwable, 
CompletableFuture<T>>
+                                                                
permitAcquireErrorHandler) {
+        return 
AsyncDualMemoryLimiterUtil.withPermitsFuture(update(initialPermit, 
newMemorySize, isCancelled), function,
+                permitAcquireErrorHandler, this::release);
+    }
+}
+```
+
+#### AsyncDualMemoryLimiterUtil Helper
+
+A utility class provides helper methods for common patterns:
+
+```java
+public class AsyncDualMemoryLimiterUtil {
+    /**
+     * Execute a function with acquired permits and ensure permits are 
released after completion.
+     * This method handles the lifecycle of permits - acquisition, usage, and 
release, including error cases.
+     *
+     * @param permitsFuture             Future that will complete with the 
required permits
+     * @param function                  Function to execute once permits are 
acquired that returns a CompletableFuture
+     * @param permitAcquireErrorHandler Handler for permit acquisition errors 
that returns a CompletableFuture
+     * @param releaser                  Consumer that handles releasing the 
permits
+     * @param <T>                       The type of result returned by the 
function
+     * @return CompletableFuture that completes with the result of the 
function execution
+     */
+    public static <T> CompletableFuture<T> withPermitsFuture(
+            CompletableFuture<AsyncDualMemoryLimiterPermit>
+                    permitsFuture,
+            Function<AsyncDualMemoryLimiterPermit,
+                    CompletableFuture<T>> function,
+            Function<Throwable, CompletableFuture<T>>
+                    permitAcquireErrorHandler,
+            Consumer<AsyncDualMemoryLimiterPermit> releaser) {
+        // implementation omitted from PIP document
+    }
+
+    /**
+     * Acquires permits and writes the command as a response to the channel.
+     * Releases the permits after the response has been written to the socket 
or if the write fails.
+     *
+     * @param ctx the channel handler context used for writing the response
+     * @param dualMemoryLimiter the memory limiter used to acquire and release 
memory permits
+     * @param isCancelled supplier that indicates if the permit acquisition 
should be cancelled
+     * @param command the base command to serialize and write to the channel
+     * @param permitAcquireErrorHandler handler for errors that occur during 
permit acquisition
+     * @return a future that completes when the command has been written to 
the channel's outbound buffer
+     */
+    public static CompletableFuture<Void> 
acquireDirectMemoryPermitsAndWriteAndFlush(ChannelHandlerContext ctx,
+                                                                               
      AsyncDualMemoryLimiter
+                                                                               
              dualMemoryLimiter,
+                                                                               
      BooleanSupplier isCancelled,
+                                                                               
      BaseCommand command,
+                                                                               
      Consumer<Throwable>
+                                                                               
              permitAcquireErrorHandler
+    ) {
+        // implementation omitted from PIP document
+    }
 }
 ```
 
 #### Integration Points
 
-**1. Heap Memory Limiting (Post-Retrieval)**
+**1. Heap Memory Limiting (Post-Retrieval) - Broker**
 
-In `ServerCnx.handleGetTopicsOfNamespace`:
+In `ServerCnx.handleGetTopicsOfNamespace`, the implementation uses the helper 
methods:
 
 ```java
-// Acquire a fixed amount of permits initially since it's not known how much 
memory will be used
-// This will ensure that the operation continues only after it has the initial 
permits
-// It would be possible to use statistics for initial estimate, but this is 
simpler and sufficient
-maxTopicListInFlightLimiter.acquire(INITIAL_SIZE, 
AsyncDualMemoryLimiter.LimitType.HEAP_MEMORY)
-    .thenCompose(initialPermit -> {
-        
getBrokerService().pulsar().getNamespaceService().getListOfUserTopics(namespaceName,
 mode)
-            .thenCompose(topics -> {
-                // Estimate memory after retrieval and update the permits to 
reflect the actual size
-                long estimatedSize = 
topics.stream().mapToInt(String::length).sum();
-                return maxTopicListInFlightLimiter
-                    .update(initialPermit, estimatedSize)
-                    .thenApply(permit -> Pair.of(topics, permit));
-            })
-            .thenAccept(topicsAndPermit -> {
-                try {
-                    // Process and send response
-                    ...
-                } finally {
-                    
maxTopicListInFlightLimiter.release(topicsAndPermit.getRight());
-                }
+    private void internalHandleGetTopicsOfNamespace(String namespace, 
NamespaceName namespaceName, long requestId,
+                                                    
CommandGetTopicsOfNamespace.Mode mode,
+                                                    Optional<String> 
topicsPattern, Optional<String> topicsHash,
+                                                    Semaphore lookupSemaphore) 
{
+    BooleanSupplier isPermitRequestCancelled = () -> 
!ctx().channel().isActive();
+    
maxTopicListInFlightLimiter.withAcquiredPermits(INITIAL_TOPIC_LIST_HEAP_PERMITS_SIZE,
+            AsyncDualMemoryLimiter.LimitType.HEAP_MEMORY, 
isPermitRequestCancelled, initialPermits -> {
+                return 
getBrokerService().pulsar().getNamespaceService().getListOfUserTopics(namespaceName,
 mode)
+                        .thenAccept(topics -> {
+                            long actualSize = 
topics.stream().mapToInt(String::length).sum();
+                            
maxTopicListInFlightLimiter.withUpdatedPermits(initialPermits, actualSize,
+                                    isPermitRequestCancelled, permits -> {
+                                        boolean filterTopics = false;
+                                        // filter system topic
+                                        List<String> filteredTopics = topics;
+
+                                        if 
(enableSubscriptionPatternEvaluation && topicsPattern.isPresent()) {
+                                            if (topicsPattern.get().length() 
<= maxSubscriptionPatternLength) {
+                                                filterTopics = true;
+                                                filteredTopics = 
TopicList.filterTopics(filteredTopics, topicsPattern.get(),
+                                                        
topicsPatternImplementation);
+                                            } else {
+                                                log.info("[{}] Subscription 
pattern provided [{}] was longer than "
+                                                                + "maximum 
{}.", remoteAddress, topicsPattern.get(),
+                                                        
maxSubscriptionPatternLength);
+                                            }
+                                        }
+                                        String hash = 
TopicList.calculateHash(filteredTopics);
+                                        boolean hashUnchanged = 
topicsHash.isPresent() && topicsHash.get().equals(hash);
+                                        if (hashUnchanged) {
+                                            filteredTopics = 
Collections.emptyList();
+                                        }
+                                        if (log.isDebugEnabled()) {
+                                            log.debug("[{}] Received 
CommandGetTopicsOfNamespace for namespace "
+                                                            + "[//{}] by {}, 
size:{}", remoteAddress, namespace,
+                                                    requestId,
+                                                    topics.size());
+                                        }
+                                        
commandSender.sendGetTopicsOfNamespaceResponse(filteredTopics, hash, 
filterTopics,
+                                                !hashUnchanged, requestId, ex 
-> {
+                                                    log.warn("[{}] Failed to 
acquire direct memory permits for "
+                                                            + 
"GetTopicsOfNamespace: {}", remoteAddress, ex.getMessage());
+                                                    
commandSender.sendErrorResponse(requestId, ServerError.TooManyRequests,
+                                                            "Cannot acquire 
permits for direct memory");
+                                                });
+                                        return 
CompletableFuture.completedFuture(null);
+                                    }, t -> {
+                                        log.warn("[{}] Failed to acquire heap 
memory permits for "
+                                                + "GetTopicsOfNamespace: {}", 
remoteAddress, t.getMessage());
+                                        
writeAndFlush(Commands.newError(requestId, ServerError.TooManyRequests,
+                                                "Failed due to heap memory 
limit exceeded"));
+                                        return 
CompletableFuture.completedFuture(null);
+                                    });
+                        }).whenComplete((__, ___) -> {
+                            lookupSemaphore.release();
+                        }).exceptionally(ex -> {
+                            log.warn("[{}] Error GetTopicsOfNamespace for 
namespace [//{}] by {}", remoteAddress,
+                                    namespace, requestId);
+                            commandSender.sendErrorResponse(requestId,
+                                    
BrokerServiceException.getClientErrorCode(new ServerMetadataException(ex)),
+                                    ex.getMessage());
+                            return null;
+                        });
+            }, t -> {
+                log.warn("[{}] Failed to acquire initial heap memory permits 
for GetTopicsOfNamespace: {}",
+                        remoteAddress, t.getMessage());
+                writeAndFlush(Commands.newError(requestId, 
ServerError.TooManyRequests,
+                        "Failed due to heap memory limit exceeded"));
+                lookupSemaphore.release();
+                return CompletableFuture.completedFuture(null);
             });
-        ...
-    // For exceptional paths, initialPermit would need to be released
+}
 ```
 
-**2. Direct Memory Limiting (Pre-Serialization)**
+**2. Direct Memory Limiting (Pre-Serialization) - Broker**
 
-Modified `CommandSender` implementation:
+Modified `PulsarCommandSenderImpl`:
 
 ```java
 @Override
 public void sendGetTopicsOfNamespaceResponse(List<String> topics, String 
topicsHash,
-                                             boolean filtered, boolean 
changed, long requestId) {
+                                             boolean filtered, boolean 
changed, long requestId,
+                                             Consumer<Throwable> 
permitAcquireErrorHandler) {
     BaseCommand command = 
Commands.newGetTopicsOfNamespaceResponseCommand(topics, topicsHash,
             filtered, changed, requestId);
     safeIntercept(command, cnx);
-    acquireMaxTopicListInFlightPermitsAndWriteAndFlush(command);
+    acquireDirectMemoryPermitsAndWriteAndFlush(cnx.ctx(), 
maxTopicListInFlightLimiter, () -> !cnx.isActive(),
+            command, permitAcquireErrorHandler);
 }
+```
+
+The utility method implementation:
 
-private void acquireMaxTopicListInFlightPermitsAndWriteAndFlush(BaseCommand 
command) {
+```java
+public static CompletableFuture<Void> 
acquireDirectMemoryPermitsAndWriteAndFlush(ChannelHandlerContext ctx,
+                                                                               
      AsyncDualMemoryLimiter
+                                                                               
              dualMemoryLimiter,
+                                                                               
      BooleanSupplier isCancelled,
+                                                                               
      BaseCommand command,
+                                                                               
      Consumer<Throwable>
+                                                                               
              permitAcquireErrorHandler
+) {
     // Calculate serialized size before acquiring permits
     int serializedSize = command.getSerializedSize();
     // Acquire permits
-    maxTopicListInFlightLimiter.acquire(serializedSize, 
AsyncDualMemoryLimiter.LimitType.DIRECT_MEMORY)
-            .thenAcceptAsync(permits -> {
+    return dualMemoryLimiter.acquire(serializedSize, 
AsyncDualMemoryLimiter.LimitType.DIRECT_MEMORY, isCancelled)
+            .whenComplete((permits, t) -> {
+                if (t != null) {
+                    permitAcquireErrorHandler.accept(t);
+                    return;
+                }
                 try {
                     // Serialize the response
                     ByteBuf outBuf = 
Commands.serializeWithPrecalculatedSerializedSize(command, serializedSize);
                     // Write the response
-                    cnx.ctx().writeAndFlush(outBuf).addListener(future -> {
+                    ctx.writeAndFlush(outBuf).addListener(future -> {
                         // Release permits after the response has been written 
to the socket
-                        maxTopicListInFlightLimiter.release(permits);
+                        dualMemoryLimiter.release(permits);
                     });
-                } catch (Exception e) {
+                } catch (Throwable e) {
                     // Return permits if an exception occurs before 
writeAndFlush is called successfully
-                    maxTopicListInFlightLimiter.release(permits);
+                    dualMemoryLimiter.release(permits);
                     throw e;
                 }
-            }, cnx.ctx().executor());
+            }).thenApply(__ -> null);
 }
 ```
 
-**3. Watch Command Memory Control**
+**3. Watch Command Memory Control - Broker**
 
-Similar memory limiting patterns apply to watch commands:
+Similar memory limiting patterns apply to watch commands in `TopicListService`:
 
 ```java
-public void sendWatchTopicListSuccess(long requestId, long watcherId, String 
topicsHash, List<String> topics) {
-    BaseCommand command = Commands.newWatchTopicListSuccess(requestId, 
watcherId, topicsHash, topics);
-    acquireMaxTopicListInFlightPermitsAndWriteAndFlush(command);
-}
-
-public void sendWatchTopicListUpdate(long watcherId, List<String> newTopics, 
List<String> deletedTopics, String topicsHash) {
-    BaseCommand command = Commands.newWatchTopicUpdate(watcherId, newTopics, 
deletedTopics, topicsHash);
-    acquireMaxTopicListInFlightPermitsAndWriteAndFlush(command);
+public void sendTopicListUpdate(long watcherId, String topicsHash, 
+                               List<String> deletedTopics, List<String> 
newTopics) {
+    connection.getCommandSender().sendWatchTopicListUpdate(
+        watcherId, newTopics, deletedTopics, topicsHash,
+        t -> {
+            log.warn("[{}] Cannot acquire direct memory tokens for sending 
topic list update",
+                connection.toString(), t);
+        });
 }
 ```
 
-**4. Proxy Reading Memory Control**
-
-On the Pulsar Proxy side, the problem is slightly different. The problem 
occurs when the proxy receives a `CommandGetTopicsOfNamespace` command, 
forwards it to a broker, and receives a response. The proxy needs to 
deserialize and serialize the response before sending it to the client.
-Memory is allocated for both deserialization and serialization.
-
-Solving this requires a slight modification to PulsarDecoder.
+**4. Proxy Memory Control**
 
-In `PulsarDecoder.channelRead`, it would be necessary to record the size of 
the incoming message:
+On the Pulsar Proxy side in `LookupProxyHandler`:
 
 ```java
-        // Get a buffer that contains the full frame
-        ByteBuf buffer = (ByteBuf) msg;
-        try {
-            // De-serialize the command
-            int cmdSize = (int) buffer.readUnsignedInt();
-            cmd.parseFrom(buffer, cmdSize);
-```
+private void internalPerformGetTopicsOfNamespace(long clientRequestId, String 
namespaceName, ClientCnx clientCnx,
+                                                     ByteBuf command, long 
requestId) {
+    BooleanSupplier isPermitRequestCancelled = () -> 
!proxyConnection.ctx().channel().isActive();
+    
maxTopicListInFlightLimiter.withAcquiredPermits(INITIAL_TOPIC_LIST_HEAP_PERMITS_SIZE,
+            AsyncDualMemoryLimiter.LimitType.HEAP_MEMORY, 
isPermitRequestCancelled, initialPermits -> {
+                return clientCnx.newGetTopicsOfNamespace(command, 
requestId).whenComplete((r, t) -> {
+                    if (t != null) {
+                        log.warn("[{}] Failed to get TopicsOfNamespace {}: 
{}", clientAddress, namespaceName,
+                                t.getMessage());
+                        writeAndFlush(Commands.newError(clientRequestId, 
getServerError(t), t.getMessage()));
+                    } else {
+                        long actualSize =
+                                
r.getNonPartitionedOrPartitionTopics().stream().mapToInt(String::length).sum();
+                        
maxTopicListInFlightLimiter.withUpdatedPermits(initialPermits, actualSize,
+                                isPermitRequestCancelled, permits -> {
+                                    return 
handleWritingGetTopicsResponse(clientRequestId, r, isPermitRequestCancelled);
+                                }, t2 -> {
+                                    log.warn("[{}] Failed to acquire actual 
heap memory permits for "
+                                            + "GetTopicsOfNamespace: {}", 
clientAddress, t2.getMessage());
+                                    
writeAndFlush(Commands.newError(clientRequestId, ServerError.TooManyRequests,
+                                            "Failed due to heap memory limit 
exceeded"));
+
+                                    return 
CompletableFuture.completedFuture(null);
+                                });
+                    }
+                }).thenApply(__ -> null);
+            }, t -> {
+                log.warn("[{}] Failed to acquire initial heap memory permits 
for GetTopicsOfNamespace: {}",
+                        clientAddress, t.getMessage());
+                writeAndFlush(Commands.newError(clientRequestId, 
ServerError.TooManyRequests,
+                        "Failed due to heap memory limit exceeded"));
+
+                return CompletableFuture.completedFuture(null);
+            }).exceptionally(ex -> {
+        writeAndFlush(Commands.newError(clientRequestId, getServerError(ex), 
ex.getMessage()));
+        return null;
+    });
+}
 
-It could be modified to store the `cmdSize` in a field instead of a local 
variable:
-```java
-    protected int cmdSize;
-...
-        // Get a buffer that contains the full frame
-        ByteBuf buffer = (ByteBuf) msg;
-        try {
-            // De-serialize the command
-            cmdSize = (int) buffer.readUnsignedInt();
-            cmd.parseFrom(buffer, cmdSize);
+private CompletableFuture<Void> handleWritingGetTopicsResponse(long 
clientRequestId, GetTopicsResult r,
+                                                               BooleanSupplier 
isCancelled) {
+    BaseCommand responseCommand = 
Commands.newGetTopicsOfNamespaceResponseCommand(
+            r.getNonPartitionedOrPartitionTopics(), r.getTopicsHash(), 
r.isFiltered(),
+            r.isChanged(), clientRequestId);
+    return acquireDirectMemoryPermitsAndWriteAndFlush(proxyConnection.ctx(), 
maxTopicListInFlightLimiter,
+            isCancelled, responseCommand, t -> {
+                log.warn("[{}] Failed to acquire actual direct memory permits 
for GetTopicsOfNamespace: {}",
+                        clientAddress, t.getMessage());
+                writeAndFlush(Commands.newError(clientRequestId, 
ServerError.TooManyRequests,
+                        "Failed due to heap memory limit exceeded"));

Review Comment:
   ```java
   "Failed due to direct memory limit exceeded"
   ```



##########
pulsar-proxy/src/main/java/org/apache/pulsar/proxy/server/LookupProxyHandler.java:
##########
@@ -357,6 +358,62 @@ private void performGetTopicsOfNamespace(long 
clientRequestId,
         });
     }
 
+    private void internalPerformGetTopicsOfNamespace(long clientRequestId, 
String namespaceName, ClientCnx clientCnx,
+                                                     ByteBuf command, long 
requestId) {
+        BooleanSupplier isPermitRequestCancelled = () -> 
!proxyConnection.ctx().channel().isActive();
+        
maxTopicListInFlightLimiter.withAcquiredPermits(INITIAL_TOPIC_LIST_HEAP_PERMITS_SIZE,
+                AsyncDualMemoryLimiter.LimitType.HEAP_MEMORY, 
isPermitRequestCancelled, initialPermits -> {
+                    return clientCnx.newGetTopicsOfNamespace(command, 
requestId).whenComplete((r, t) -> {
+                        if (t != null) {
+                            log.warn("[{}] Failed to get TopicsOfNamespace {}: 
{}", clientAddress, namespaceName,
+                                    t.getMessage());
+                            writeAndFlush(Commands.newError(clientRequestId, 
getServerError(t), t.getMessage()));
+                        } else {
+                            long actualSize =
+                                    
r.getNonPartitionedOrPartitionTopics().stream()
+                                            .mapToInt(ByteBufUtil::utf8Bytes) 
// convert character count to bytes
+                                            .map(n -> n + 32) // add 32 bytes 
overhead for each entry

Review Comment:
   Can be changed to
   ```java
   .mapToLong(topic -> ByteBufUtil.utf8Bytes(topic) + 32) // UTF-8 bytes + 32 
bytes overhead per entry
   ```



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