mmodzelewski commented on code in PR #2711:
URL: https://github.com/apache/iggy/pull/2711#discussion_r2812417028
##########
examples/java/README.md:
##########
@@ -64,6 +64,112 @@ You can also customize the server using environment
variables:
IGGY_HTTP_ENABLED=true IGGY_TCP_ADDRESS=0.0.0.0:8090 cargo run --bin
iggy-server
```
+## Blocking vs. Async - When to Use Each
Review Comment:
I think this section belongs further down. We should aim for a logical flow,
starting with the basics and moving on to the more advanced concepts.
##########
examples/java/README.md:
##########
@@ -64,6 +64,112 @@ You can also customize the server using environment
variables:
IGGY_HTTP_ENABLED=true IGGY_TCP_ADDRESS=0.0.0.0:8090 cargo run --bin
iggy-server
```
+## Blocking vs. Async - When to Use Each
+
+The Iggy Java SDK provides two client types: **blocking (synchronous)** and
**async (non-blocking)**. Choose based on your use case:
+
+### Use Blocking Client When
+
+- Message rate < 1000/sec
+- Writing scripts, CLI tools, or simple applications
+- Sequential code is easier to reason about
+- Integration tests
+
+### Use Async Client When
+
+- Need > 5000 msg/sec throughput
+- Application is already async/reactive (Spring WebFlux, Vert.x)
+- Want to pipeline multiple requests over a single connection
+- Building services that handle many concurrent streams
+
+### Performance Characteristics
+
+**Blocking Client:**
+
+- Throughput: ~5,000 msg/sec (varies with batch size, network latency)
+- Thread usage: One thread per operation
+- Latency: Low (one request at a time)
+
+**Async Client:**
+
+- Throughput: ~20,000+ msg/sec (with pipelining)
Review Comment:
I'd refrain from including a specific message count, at least until we've
done some proper benchmarking. Secondly, this depends heavily on the message
size.
##########
examples/java/README.md:
##########
@@ -132,18 +238,53 @@ Building streams with advanced configuration:
Shows how to use the stream builder API to create and configure streams with
custom settings.
-## Async Client
+## Key Async Patterns
-The following example demonstrates how to use the asynchronous client:
+### CompletableFuture Chaining
-Async producer example:
-
-```bash
-./gradlew runAsyncProducer
+```java
+client.connect()
+ .thenCompose(v -> client.login())
+ .thenCompose(identity -> client.streams().createStream("my-stream"))
+ .thenAccept(stream -> System.out.println("Created: " + stream.name()))
+ .exceptionally(ex -> {
+ System.err.println("Error: " + ex.getMessage());
+ return null;
+ });
```
-Async consumer example:
+### Pipelining for Throughput
-```bash
-./gradlew runAsyncConsumerExample
+```java
+List<CompletableFuture<Void>> sends = new ArrayList<>();
+for (int i = 0; i < 10; i++) {
+ sends.add(client.messages().sendMessages(...));
+}
+CompletableFuture.allOf(sends.toArray(new CompletableFuture[0])).join();
+```
+
+### Thread Pool Offloading
+
+```java
+// WRONG - blocks Netty event loop
+client.messages().pollMessages(...)
+ .thenAccept(polled -> {
+ saveToDatabase(polled); // blocking I/O!
+ });
+
+// CORRECT - offloads to processing pool
+var processingPool = Executors.newFixedThreadPool(8);
+client.messages().pollMessages(...)
+ .thenAcceptAsync(polled -> {
+ saveToDatabase(polled); // runs on processingPool
+ }, processingPool);
```
+
+## Next Steps
Review Comment:
I'd remove this section entirely, as it's a bit redundant and doesn't add
anything new.
##########
examples/java/src/main/java/org/apache/iggy/examples/blocking/BlockingConsumer.java:
##########
@@ -0,0 +1,184 @@
+/*
+ * 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.iggy.examples.blocking;
+
+import org.apache.iggy.Iggy;
+import org.apache.iggy.client.blocking.tcp.IggyTcpClient;
+import org.apache.iggy.consumergroup.Consumer;
+import org.apache.iggy.identifier.StreamId;
+import org.apache.iggy.identifier.TopicId;
+import org.apache.iggy.message.Message;
+import org.apache.iggy.message.PolledMessages;
+import org.apache.iggy.message.PollingStrategy;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.Optional;
+
+/**
+ * Blocking Consumer Example
+ *
+ * <p>Demonstrates message consumption using the blocking (synchronous) Iggy
client.
+ *
+ * <p>This example shows:
+ *
+ * <ul>
+ * <li>Connection and authentication</li>
+ * <li>Continuous message polling from a specific partition</li>
+ * <li>Offset-based consumption</li>
+ * <li>Graceful shutdown</li>
+ * </ul>
+ *
+ * <p>Run this after running BlockingProducer to see messages flow through.
+ *
+ * <p>Run with: {@code ./gradlew runBlockingConsumer}
+ */
+public final class BlockingConsumer {
Review Comment:
Other than the documentation, I don't see how this differs from the
gettingstarted/consumer example.
##########
examples/java/src/main/java/org/apache/iggy/examples/async/AsyncProducer.java:
##########
@@ -29,183 +30,239 @@
import org.slf4j.LoggerFactory;
import java.math.BigInteger;
+import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
-import java.util.UUID;
import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.ExecutionException;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicInteger;
/**
- * AsyncProducer demonstrates how to use the async client to send messages to
Apache Iggy.
- * This producer sends messages asynchronously and handles responses using
CompletableFuture.
+ * Async Producer Example - High Throughput
+ *
+ * <p>Demonstrates high-throughput message production using the async
(non-blocking) Iggy client.
+ *
+ * <h2>WHEN TO USE THE ASYNC CLIENT:</h2>
+ * <ul>
+ * <li>You need > 5000 msg/sec throughput</li>
+ * <li>Your application is already async/reactive (Spring WebFlux, Vert.x,
etc.)</li>
+ * <li>You want to pipeline multiple requests over a single connection</li>
+ * <li>You're building a service that handles many concurrent streams</li>
+ * </ul>
+ *
+ * <h2>KEY DIFFERENCES FROM BLOCKING CLIENT:</h2>
+ * <ul>
+ * <li>All methods return CompletableFuture instead of direct values</li>
+ * <li>Built on Netty's non-blocking I/O (no thread-per-request)</li>
+ * <li>Can pipeline multiple send operations without waiting for each to
complete</li>
+ * <li>Single connection handles all concurrent requests via event loop
multiplexing</li>
+ * </ul>
+ *
+ * <h2>PERFORMANCE CHARACTERISTICS:</h2>
+ * <ul>
+ * <li>Throughput: Higher (pipelines requests, no thread contention)</li>
+ * <li>Latency per request: Similar to blocking</li>
+ * <li>Thread usage: Minimal (Netty event loop threads)</li>
+ * <li>Code complexity: Higher (futures, callbacks)</li>
+ * </ul>
+ *
+ * <p>This example shows:
+ * <ul>
+ * <li>Async client setup with CompletableFuture chaining</li>
+ * <li>Pipelined message sending (fire multiple sends without blocking)</li>
+ * <li>Error handling with exceptionally()</li>
+ * <li>Performance measurement</li>
+ * <li>Proper async shutdown</li>
+ * </ul>
+ *
+ * <p>Run with: {@code ./gradlew runAsyncProducer}
*/
-public class AsyncProducer {
+public final class AsyncProducer {
private static final Logger log =
LoggerFactory.getLogger(AsyncProducer.class);
- private static final String HOST = "127.0.0.1";
- private static final int PORT = 8090;
+ // Configuration
+ private static final String IGGY_HOST = "localhost";
+ private static final int IGGY_PORT = 8090;
private static final String USERNAME = "iggy";
private static final String PASSWORD = "iggy";
+ private static final String STREAM_NAME = "async-example-stream";
+ private static final String TOPIC_NAME = "async-example-topic";
+ private static final int PARTITION_COUNT = 3;
- private static final String STREAM_NAME = "async-test";
- private static final String TOPIC_NAME = "events";
- private static final long PARTITION_ID = 0L;
+ // High-throughput configuration
+ private static final int MESSAGE_BATCH_SIZE = 500; // Larger batches for
async
+ private static final int TOTAL_BATCHES = 20;
+ private static final int MAX_IN_FLIGHT = 5; // Pipeline up to 5 concurrent
sends
- private static final int MESSAGE_COUNT = 100;
- private static final int MESSAGE_SIZE = 256;
+ private AsyncProducer() {
+ // Utility class
+ }
- private final AsyncIggyTcpClient client;
- private final AtomicInteger successCount = new AtomicInteger(0);
- private final AtomicInteger errorCount = new AtomicInteger(0);
+ public static void main(String[] args) {
+ AsyncIggyTcpClient client = null;
- public AsyncProducer() {
- this.client = new AsyncIggyTcpClient(HOST, PORT);
- }
+ try {
+ log.info("=== Async Producer Example (High Throughput) ===");
- public CompletableFuture<Void> start() {
- log.info("Starting AsyncProducer...");
+ // 1. Build, connect, and login - all chained with
CompletableFuture
+ log.info("Connecting to Iggy server at {}:{}...", IGGY_HOST,
IGGY_PORT);
- return client.connect()
- .thenCompose(v -> {
- log.info("Connected to Iggy server at {}:{}", HOST, PORT);
- return client.users().login(USERNAME, PASSWORD);
- })
- .thenCompose(v -> {
- log.info("Logged in successfully as user: {}", USERNAME);
- return setupStreamAndTopic();
- })
- .thenCompose(v -> {
- log.info("Stream and topic setup complete");
- return sendMessages();
- })
- .thenRun(() -> {
- log.info("All messages sent. Success: {}, Errors: {}",
successCount.get(), errorCount.get());
- })
- .exceptionally(ex -> {
- log.error("Error in producer flow", ex);
- return null;
- });
+ // ASYNC PATTERN: Use join() only at the end to block until client
is ready.
+ // In a real async app (e.g. Spring WebFlux), you'd chain
everything without join().
+ client = Iggy.tcpClientBuilder()
+ .async()
+ .host(IGGY_HOST)
+ .port(IGGY_PORT)
+ .credentials(USERNAME, PASSWORD)
+ .buildAndLogin()
+ .join(); // Block here to wait for connection
+
+ log.info("Connected successfully");
+
+ // 2. Setup stream and topic
+ AsyncIggyTcpClient finalClient = client;
+ setupStreamAndTopic(finalClient).join();
+
+ // 3. Send messages with pipelining
+ sendMessagesAsync(finalClient).join();
+
+ log.info("=== Producer completed successfully ===");
+
+ } catch (RuntimeException e) {
+ log.error("Producer failed", e);
+ System.exit(1);
+ } finally {
+ // Always close the client
+ if (client != null) {
+ try {
+ client.close().join();
+ log.info("Client closed");
+ } catch (RuntimeException e) {
+ log.error("Error closing client", e);
+ }
+ }
+ }
}
- private CompletableFuture<Void> setupStreamAndTopic() {
- log.info("Checking stream: {}", STREAM_NAME);
+ private static CompletableFuture<Void>
setupStreamAndTopic(AsyncIggyTcpClient client) {
+ // ASYNC CHAINING PATTERN:
+ // Each operation returns CompletableFuture. We chain them with
thenCompose().
+ // Errors propagate down the chain and can be handled with
exceptionally().
return client.streams()
.getStream(StreamId.of(STREAM_NAME))
- .thenCompose(stream -> {
- if (stream.isEmpty()) {
- log.info("Creating stream: {}", STREAM_NAME);
- return client.streams()
- .createStream(STREAM_NAME)
- .thenAccept(created -> log.info("Stream
created: {}", created.name()));
- } else {
- log.info("Stream exists: {}", STREAM_NAME);
- return CompletableFuture.completedFuture(null);
- }
+ .thenApply(stream -> {
+ log.info("Stream '{}' already exists", STREAM_NAME);
Review Comment:
This flow does not look right. `getStream` returns optional, so you should
check what's inside the optional. Later, there's `creating stream` log message
within `exceptionally`, which actually won't be called. Please review and
update this flow.
##########
examples/java/src/main/java/org/apache/iggy/examples/blocking/BlockingProducer.java:
##########
@@ -0,0 +1,190 @@
+/*
+ * 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.iggy.examples.blocking;
+
+import org.apache.iggy.Iggy;
+import org.apache.iggy.client.blocking.tcp.IggyTcpClient;
+import org.apache.iggy.identifier.StreamId;
+import org.apache.iggy.identifier.TopicId;
+import org.apache.iggy.message.Message;
+import org.apache.iggy.message.Partitioning;
+import org.apache.iggy.topic.CompressionAlgorithm;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.math.BigInteger;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * Blocking Producer Example
+ *
+ * <p>Demonstrates basic message production using the blocking (synchronous)
Iggy client.
+ *
+ * <h2>WHEN TO USE THE BLOCKING CLIENT:</h2>
+ * <ul>
+ * <li>Simple applications, scripts, CLI tools</li>
+ * <li>Message rate < 1000/sec</li>
+ * <li>Sequential code is easier to reason about</li>
+ * <li>Integration tests</li>
+ * </ul>
+ *
+ * <p>This example shows:
+ * <ul>
+ * <li>Client connection and authentication</li>
+ * <li>Stream and topic creation</li>
+ * <li>Batch message sending (recommended for efficiency)</li>
+ * <li>Balanced partitioning for throughput</li>
+ * <li>Proper resource cleanup</li>
+ * </ul>
+ *
+ * <p>Run with: {@code ./gradlew runBlockingProducer}
+ */
+public final class BlockingProducer {
Review Comment:
This seems like a duplicate of `gettinstarted/producer` example.
##########
examples/java/src/main/java/org/apache/iggy/examples/async/AsyncConsumer.java:
##########
@@ -0,0 +1,349 @@
+/*
+ * 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.iggy.examples.async;
+
+import org.apache.iggy.Iggy;
+import org.apache.iggy.client.async.tcp.AsyncIggyTcpClient;
+import org.apache.iggy.consumergroup.Consumer;
+import org.apache.iggy.identifier.StreamId;
+import org.apache.iggy.identifier.TopicId;
+import org.apache.iggy.message.Message;
+import org.apache.iggy.message.PolledMessages;
+import org.apache.iggy.message.PollingStrategy;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.math.BigInteger;
+import java.util.Optional;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+
+/**
+ * Async Consumer Example - Backpressure and Error Handling
+ *
+ * <p>Demonstrates advanced async message consumption patterns including:
+ * <ul>
+ * <li>Non-blocking continuous polling</li>
+ * <li>Backpressure management (don't poll faster than you can process)</li>
+ * <li>Error recovery with exponential backoff</li>
+ * <li>Offloading CPU-intensive work from Netty threads</li>
+ * <li>Graceful shutdown</li>
+ * </ul>
+ *
+ * <h2>CRITICAL ASYNC PATTERN - Thread Pool Management:</h2>
+ *
+ * <p>The async client uses Netty's event loop threads for I/O operations.
+ * <strong>NEVER</strong> block these threads with:
+ * <ul>
+ * <li>{@code .join()} or {@code .get()} inside {@code
thenApply/thenAccept}</li>
+ * <li>{@code Thread.sleep()}</li>
+ * <li>Blocking database calls</li>
+ * <li>Long-running computations</li>
+ * </ul>
+ *
+ * <p>If your message processing involves blocking operations, offload to a
separate
+ * thread pool using {@code thenApplyAsync(fn, executor)}.
+ *
+ * <p>This example shows the correct pattern.
+ *
+ * <p>Run after AsyncProducer to see messages flow.
+ *
+ * <p>Run with: {@code ./gradlew runAsyncConsumer}
+ */
+public final class AsyncConsumer {
+ private static final Logger log =
LoggerFactory.getLogger(AsyncConsumer.class);
+
+ // Configuration (must match AsyncProducer)
+ private static final String IGGY_HOST = "localhost";
+ private static final int IGGY_PORT = 8090;
+ private static final String USERNAME = "iggy";
+ private static final String PASSWORD = "iggy";
+ private static final String STREAM_NAME = "async-example-stream";
+ private static final String TOPIC_NAME = "async-example-topic";
+ private static final long PARTITION_ID = 0L;
+ private static final long CONSUMER_ID = 0L;
+
+ // Polling configuration
+ private static final int POLL_BATCH_SIZE = 100;
+ private static final int POLL_INTERVAL_MS = 1000;
+ private static final int BATCHES_LIMIT = 5; // Exit after receiving this
many batches
+ private static final int MAX_EMPTY_POLLS = 5; // Exit if no messages after
consecutive empty polls
+
+ // Error recovery configuration
+ private static final int MAX_RETRY_ATTEMPTS = 5;
+ private static final int INITIAL_BACKOFF_MS = 100;
+ private static final int MAX_BACKOFF_MS = 5000;
+
+ // Thread pool for message processing (separate from Netty threads)
+ // Size based on workload: CPU-bound = availableProcessors, I/O-bound = 2x
or more
+ private static final int PROCESSING_THREADS =
Runtime.getRuntime().availableProcessors();
+
+ private static volatile boolean running = true;
+
+ private AsyncConsumer() {
+ // Utility class
+ }
+
+ public static void main(String[] args) {
+ AsyncIggyTcpClient client = null;
+ ExecutorService processingPool = null;
+
+ // Handle Ctrl+C gracefully
+ Runtime.getRuntime().addShutdownHook(new Thread(() -> {
+ log.info("Shutdown signal received, stopping consumer...");
+ running = false;
+ }));
+
+ try {
+ log.info("=== Async Consumer Example (Backpressure + Error
Handling) ===");
+
+ // Create thread pool for message processing
+ processingPool = Executors.newFixedThreadPool(PROCESSING_THREADS,
r -> {
+ Thread t = new Thread(r, "message-processor");
+ t.setDaemon(true);
+ return t;
+ });
+
+ log.info("Created processing thread pool with {} threads",
PROCESSING_THREADS);
+
+ // 1. Connect and authenticate
+ log.info("Connecting to Iggy server at {}:{}...", IGGY_HOST,
IGGY_PORT);
+ client = Iggy.tcpClientBuilder()
+ .async()
+ .host(IGGY_HOST)
+ .port(IGGY_PORT)
+ .credentials(USERNAME, PASSWORD)
+ .buildAndLogin()
+ .join();
+
+ log.info("Connected successfully");
+
+ // 2. Poll messages continuously with backpressure
+ AsyncIggyTcpClient finalClient = client;
+ pollMessagesAsync(finalClient, processingPool).join();
+
+ log.info("=== Consumer stopped gracefully ===");
+
+ } catch (RuntimeException e) {
+ log.error("Consumer failed", e);
+ System.exit(1);
+ } finally {
+ // Cleanup
+ if (client != null) {
+ try {
+ client.close().join();
+ log.info("Client closed");
+ } catch (RuntimeException e) {
+ log.error("Error closing client", e);
+ }
+ }
+
+ if (processingPool != null) {
+ processingPool.shutdown();
+ try {
+ if (!processingPool.awaitTermination(5, TimeUnit.SECONDS))
{
+ processingPool.shutdownNow();
+ }
+ log.info("Processing thread pool shut down");
+ } catch (InterruptedException e) {
+ processingPool.shutdownNow();
+ }
+ }
+ }
+ }
+
+ private static CompletableFuture<Void> pollMessagesAsync(
+ AsyncIggyTcpClient client, ExecutorService processingPool) {
+ log.info("Starting async polling loop (limit: {} batches)...",
BATCHES_LIMIT);
+
+ AtomicInteger totalReceived = new AtomicInteger(0);
+ AtomicInteger emptyPolls = new AtomicInteger(0);
+ AtomicInteger consumedBatches = new AtomicInteger(0);
+ AtomicReference<BigInteger> offset = new
AtomicReference<>(BigInteger.ZERO);
+
+ // RECURSIVE ASYNC POLLING PATTERN:
+ // Each poll schedules the next poll after processing completes.
+ // This provides natural backpressure - we don't poll for new messages
+ // until we've finished processing the current batch.
+
+ CompletableFuture<Void> pollingLoop = new CompletableFuture<>();
+ pollBatch(client, processingPool, totalReceived, emptyPolls,
consumedBatches, offset, 0, pollingLoop);
+ return pollingLoop;
+ }
+
+ private static void pollBatch(
+ AsyncIggyTcpClient client,
+ ExecutorService processingPool,
+ AtomicInteger totalReceived,
+ AtomicInteger emptyPolls,
+ AtomicInteger consumedBatches,
+ AtomicReference<BigInteger> offset,
+ int retryAttempt,
+ CompletableFuture<Void> loopFuture) {
+ if (!running || consumedBatches.get() >= BATCHES_LIMIT) {
+ log.info(
+ "Finished consuming {} batches. Total messages received:
{}",
+ consumedBatches.get(),
+ totalReceived.get());
+ loopFuture.complete(null);
+ return;
+ }
+
+ StreamId streamId = StreamId.of(STREAM_NAME);
+ TopicId topicId = TopicId.of(TOPIC_NAME);
+ Consumer consumer = Consumer.of(CONSUMER_ID);
+
+ client.messages()
+ .pollMessages(
+ streamId,
+ topicId,
+ Optional.of(PARTITION_ID),
+ consumer,
+ PollingStrategy.offset(offset.get()),
+ (long) POLL_BATCH_SIZE,
+ false)
+ .thenComposeAsync(
+ polled -> {
+ // OFFLOAD TO PROCESSING POOL:
+ // We use thenComposeAsync with processingPool to
move message processing
+ // off the Netty event loop. This is critical for
heavy workloads.
+
+ int messageCount = polled.messages().size();
+
+ if (messageCount > 0) {
+ // Update offset for next poll
+ offset.updateAndGet(current ->
current.add(BigInteger.valueOf(messageCount)));
+ consumedBatches.incrementAndGet();
+
+ return processMessages(polled, totalReceived,
processingPool)
+ .thenRun(() -> emptyPolls.set(0));
+ } else {
+ int empty = emptyPolls.incrementAndGet();
+ if (empty >= MAX_EMPTY_POLLS) {
+ log.info("No more messages after {} empty
polls, finishing.", MAX_EMPTY_POLLS);
+ running = false;
+ return
CompletableFuture.completedFuture(null);
+ }
+ log.info("Caught up - no new messages.
Waiting...");
+ // Sleep without blocking Netty threads
+ return CompletableFuture.runAsync(
+ () -> {
+ try {
+ Thread.sleep(POLL_INTERVAL_MS);
+ } catch (InterruptedException e) {
+
Thread.currentThread().interrupt();
+ }
+ },
+ processingPool);
+ }
+ },
+ processingPool)
+ .thenRun(() -> {
+ // SUCCESS: Reset retry counter and schedule next poll
+ pollBatch(
+ client, processingPool, totalReceived, emptyPolls,
consumedBatches, offset, 0, loopFuture);
+ })
+ .exceptionally(e -> {
+ // ERROR RECOVERY WITH EXPONENTIAL BACKOFF:
+ // Don't give up on the first error. Retry with increasing
delays.
+ log.error(
+ "Error polling messages (attempt {}/{}): {}",
+ retryAttempt + 1,
+ MAX_RETRY_ATTEMPTS,
+ e.getMessage());
+
+ if (retryAttempt < MAX_RETRY_ATTEMPTS) {
+ int backoffMs = Math.min(INITIAL_BACKOFF_MS * (1 <<
retryAttempt), MAX_BACKOFF_MS);
+ log.info("Retrying in {} ms...", backoffMs);
+
+ // Schedule retry after backoff
+ CompletableFuture.runAsync(
+ () -> {
+ try {
+ Thread.sleep(backoffMs);
+ } catch (InterruptedException ie) {
+ Thread.currentThread().interrupt();
+ }
+ pollBatch(
+ client,
+ processingPool,
+ totalReceived,
+ emptyPolls,
+ consumedBatches,
+ offset,
+ retryAttempt + 1,
+ loopFuture);
+ },
+ processingPool);
+ } else {
+ log.error("Max retry attempts reached. Stopping
consumer.");
+ loopFuture.completeExceptionally(e);
+ }
+ return null;
+ });
+ }
+
+ private static CompletableFuture<Void> processMessages(
+ PolledMessages polled, AtomicInteger totalReceived,
ExecutorService processingPool) {
+ // Process each message (this runs on processingPool, not Netty
threads)
+ return CompletableFuture.runAsync(
+ () -> {
+ int messageCount = polled.messages().size();
+
+ for (Message message : polled.messages()) {
+ String payload = new String(message.payload());
+
+ // Simulate message processing (in real app: parse,
validate, store, etc.)
+ // This could be CPU-intensive or involve blocking I/O
(database, HTTP calls)
+ processMessage(payload, message.header().offset());
+ }
+
+ int total = totalReceived.addAndGet(messageCount);
+ log.info("Processed {} messages (total: {})",
messageCount, total);
+ },
+ processingPool);
+ }
+
+ private static void processMessage(String payload, java.math.BigInteger
offset) {
+ // In a real application, this would be your business logic:
+ // - Parse JSON
+ // - Validate data
+ // - Call external APIs
+ // - Update database
+ // - Send to downstream systems
+
+ // For this example, just log occasionally
+ if (offset.compareTo(java.math.BigInteger.valueOf(5)) < 0
Review Comment:
Please use imports instead of FQN.
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