sfc-gh-wtrefon commented on code in PR #10077:
URL: https://github.com/apache/nifi/pull/10077#discussion_r2303383839


##########
nifi-extension-bundles/nifi-aws-bundle/nifi-aws-kinesis/src/main/java/org/apache/nifi/processors/aws/kinesis/MemoryBoundRecordBuffer.java:
##########
@@ -0,0 +1,672 @@
+/*
+ * 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.nifi.processors.aws.kinesis;
+
+import jakarta.annotation.Nullable;
+import org.apache.nifi.logging.ComponentLog;
+import org.apache.nifi.processors.aws.kinesis.RecordBuffer.ShardBufferId;
+import org.apache.nifi.processors.aws.kinesis.RecordBuffer.ShardBufferLease;
+import software.amazon.kinesis.exceptions.InvalidStateException;
+import software.amazon.kinesis.exceptions.KinesisClientLibDependencyException;
+import software.amazon.kinesis.exceptions.ShutdownException;
+import software.amazon.kinesis.exceptions.ThrottlingException;
+import software.amazon.kinesis.processor.RecordProcessorCheckpointer;
+import software.amazon.kinesis.retrieval.KinesisClientRecord;
+
+import java.nio.ByteBuffer;
+import java.time.Duration;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.Queue;
+import java.util.Random;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static java.util.Collections.emptyList;
+
+/**
+ * A record buffer which limits the maximum memory usage across all shard 
buffers.
+ * If the memory limit is reached, adding new records will block until enough 
memory is freed.
+ */
+final class MemoryBoundRecordBuffer implements 
RecordBuffer.ForKinesisClientLibrary, RecordBuffer.ForProcessor {
+
+    private final ComponentLog logger;
+
+    private final long checkpointIntervalMillis;
+    private final BlockingMemoryTracker memoryTracker;
+
+    private final AtomicLong bufferIdCounter = new AtomicLong(0);
+    private final ConcurrentMap<ShardBufferId, ShardBuffer> shardBuffers = new 
ConcurrentHashMap<>();
+
+    /**
+     * A queue with ids shard buffers available for leasing.
+     * <p>
+     * Note: when a buffer is invalidated its id is NOT removed from the queue 
immediately.
+     */
+    private final Queue<ShardBufferId> buffersToLease = new 
ConcurrentLinkedQueue<>();
+
+    MemoryBoundRecordBuffer(final ComponentLog logger, final long 
maxMemoryBytes, final Duration checkpointInterval) {
+        this.logger = logger;
+        this.memoryTracker = new BlockingMemoryTracker(logger, maxMemoryBytes);
+        this.checkpointIntervalMillis = checkpointInterval.toMillis();
+    }
+
+    @Override
+    public ShardBufferId createBuffer(final String shardId) {
+        final ShardBufferId id = new ShardBufferId(shardId, 
bufferIdCounter.getAndIncrement());
+
+        logger.info("Creating new buffer for shard {} with id {}", shardId, 
id);
+
+        shardBuffers.put(id, new ShardBuffer(id, logger, 
checkpointIntervalMillis));
+        buffersToLease.add(id);
+        return id;
+    }
+
+    @Override
+    public void addRecords(final ShardBufferId bufferId, final 
List<KinesisClientRecord> records, final RecordProcessorCheckpointer 
checkpointer) {
+        if (records.isEmpty()) {
+            return;
+        }
+
+        final ShardBuffer buffer = shardBuffers.get(bufferId);
+        if (buffer == null) {
+            logger.debug("Buffer with id {} not found. Cannot add records with 
sequence and subsequence numbers: {}.{} - {}.{}",
+                    bufferId,
+                    records.getFirst().sequenceNumber(),
+                    records.getFirst().subSequenceNumber(),
+                    records.getLast().sequenceNumber(),
+                    records.getLast().subSequenceNumber());
+            return;
+        }
+
+        final RecordBatch recordBatch = new RecordBatch(records, checkpointer, 
calculateMemoryUsage(records));
+        memoryTracker.reserveMemory(recordBatch);
+        final boolean addedRecords = buffer.offer(recordBatch);
+
+        if (addedRecords) {
+            logger.debug("Successfully added records with sequence and 
subsequence numbers: {}.{} - {}.{} to buffer with id {}",
+                    records.getFirst().sequenceNumber(),
+                    records.getFirst().subSequenceNumber(),
+                    records.getLast().sequenceNumber(),
+                    records.getLast().subSequenceNumber(),
+                    bufferId);
+        } else {
+            logger.debug("Buffer with id {} was invalidated. Cannot add 
records with sequence and subsequence numbers: {}.{} - {}.{}",
+                    bufferId,
+                    records.getFirst().sequenceNumber(),
+                    records.getFirst().subSequenceNumber(),
+                    records.getLast().sequenceNumber(),
+                    records.getLast().subSequenceNumber());
+            // If the buffer was invalidated, we should free memory reserved 
for these records.
+            memoryTracker.freeMemory(List.of(recordBatch));
+        }
+    }
+
+    @Override
+    public void checkpointEndedShard(final ShardBufferId bufferId, final 
RecordProcessorCheckpointer checkpointer) {
+        final ShardBuffer buffer = shardBuffers.get(bufferId);
+        if (buffer == null) {
+            logger.debug("Buffer with id {} not found. Cannot checkpoint the 
ended shard", bufferId);
+            return;
+        }
+
+        logger.info("Finishing consumption for buffer {}. Checkpointing the 
ended shard", bufferId);
+        buffer.checkpointEndedShard(checkpointer);
+
+        logger.debug("Removing buffer with id {} after successful ended shard 
checkpoint", bufferId);
+        shardBuffers.remove(bufferId);
+    }
+
+    @Override
+    public void shutdownShardConsumption(final ShardBufferId bufferId, final 
RecordProcessorCheckpointer checkpointer) {
+        final ShardBuffer buffer = shardBuffers.get(bufferId);
+        if (buffer == null) {
+            logger.debug("Buffer with id {} not found. Cannot shutdown shard 
consumption", bufferId);
+            return;
+        }
+
+        logger.info("Shutting down the buffer {}. Checkpointing last consumed 
record", bufferId);
+        buffer.shutdownBuffer(checkpointer);
+
+        logger.debug("Removing buffer with id {} after successful last 
consumed record checkpoint", bufferId);
+        shardBuffers.remove(bufferId);
+    }
+
+    @Override
+    public void consumerLeaseLost(final ShardBufferId bufferId) {
+        final ShardBuffer buffer = shardBuffers.remove(bufferId);
+
+        logger.info("Lease lost for buffer {}. Invalidating it", bufferId);
+
+        if (buffer != null) {
+            final Collection<RecordBatch> invalidatedBatches = 
buffer.invalidate();
+            memoryTracker.freeMemory(invalidatedBatches);
+        }
+    }
+
+    @Override
+    public Optional<ShardBufferLease> acquireBufferLease() {
+        final Set<ShardBufferId> seenBuffers = new HashSet<>();
+
+        while (true) {
+            final ShardBufferId bufferId = buffersToLease.poll();
+            if (bufferId == null) {
+                // The queue is empty or all buffers were seen already. 
Nothing to consume.
+                return Optional.empty();
+            }
+
+            if (seenBuffers.contains(bufferId)) {
+                // If the same buffer is seen again, there is a high chance we 
iterated through most of the buffers and didn't find any that isn't empty.
+                // To avoid burning CPU we return empty here, even if some 
buffer received records in the meantime. It will be picked up in the next 
iteration.
+                buffersToLease.add(bufferId);
+                return Optional.empty();
+            }
+
+            final ShardBuffer buffer = shardBuffers.get(bufferId);
+
+            if (buffer == null) {
+                // By the time the bufferId is polled, it might have been 
invalidated. No need to return it to the queue.
+                logger.debug("Buffer with id {} was removed while polling for 
lease. Continuing to poll.", bufferId);
+            } else if (buffer.isEmpty()) {
+                seenBuffers.add(bufferId);
+                buffersToLease.add(bufferId);
+                logger.debug("Buffer with id {} is empty. Continuing to 
poll.", bufferId);
+            } else {
+                logger.debug("Acquired lease for buffer {}", bufferId);
+                return Optional.of(new StandardShardBufferLease(bufferId));
+            }
+        }
+    }
+
+    @Override
+    public List<KinesisClientRecord> consumeRecords(final ShardBufferLease 
lease) {
+        if (!(lease instanceof StandardShardBufferLease l)) {

Review Comment:
   for the sake of readability i would consider renaming it
   ```suggestion
           if (!(lease instanceof StandardShardBufferLease standardLease)) {
   ```



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