atharvalade commented on code in PR #2711: URL: https://github.com/apache/iggy/pull/2711#discussion_r2818208687
########## 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: replaced all FQN usages -- This is an automated message from the Apache Git Service. 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