spring-projectsGH-8582:Transactional support in PostgresSubscribableChannel

Author: igorlovich

spring-integration-jdbc/src/main/java/org/springframework/integration/jdbc/channel/PostgresChannelMessageTableSubscriber.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 the original author or authors.
+ * Copyright 2022-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,6 +26,7 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
+import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.TimeUnit;
 
 import org.postgresql.PGNotification;
@@ -59,6 +60,7 @@
  *
  * @author Rafael Winterhalter
  * @author Artem Bilan
+ * @author Igor Lovich
  *
  * @since 6.0
  */
@@ -77,6 +79,8 @@ public final class PostgresChannelMessageTableSubscriber implements SmartLifecyc
 
 	private CountDownLatch latch = new CountDownLatch(0);
 
+	private boolean userProvidedExecutor = false;
+
 	private Future<?> future = CompletableFuture.completedFuture(null);
 
 	@Nullable
@@ -143,12 +147,17 @@ public synchronized void start() {
 		ExecutorService executorToUse = this.executor;
 		if (executorToUse == null) {
 			CustomizableThreadFactory threadFactory =
-					new CustomizableThreadFactory("postgres-channel-message-table-subscriber-");
+					new CustomizableThreadFactory("postgres-channel-notifications-");
 			threadFactory.setDaemon(true);
-			executorToUse = Executors.newSingleThreadExecutor(threadFactory);
+			executorToUse = Executors.newFixedThreadPool(2, threadFactory);
 			this.executor = executorToUse;
 		}
+		else {
+			this.userProvidedExecutor = true;
+		}
 		this.latch = new CountDownLatch(1);
+
+		CountDownLatch startingLatch = new CountDownLatch(1);
 		this.future = executorToUse.submit(() -> {
 			try {
 				while (isActive()) {
@@ -166,11 +175,13 @@ public synchronized void start() {
 							}
 							throw ex;
 						}
-						this.subscriptionsMap.values()
-								.forEach(subscriptions -> subscriptions.forEach(Subscription::notifyUpdate));
+						this.subscriptionsMap.values().forEach(this::notifyAll);
+
 						try {
 							this.connection = conn;
 							while (isActive()) {
+								startingLatch.countDown();
+
 								PGNotification[] notifications = conn.getNotifications(0);
 								// Unfortunately, there is no good way of interrupting a notification
 								// poll but by closing its connection.
@@ -184,9 +195,7 @@ public synchronized void start() {
 										if (subscriptions == null) {
 											continue;
 										}
-										for (Subscription subscription : subscriptions) {
-											subscription.notifyUpdate();
-										}
+										notifyAll(subscriptions);
 									}
 								}
 							}
@@ -208,6 +217,29 @@ public synchronized void start() {
 				this.latch.countDown();
 			}
 		});
+
+		try {
+			if (!startingLatch.await(5, TimeUnit.SECONDS)) {
+				throw new IllegalStateException("Failed to start "
+						+ PostgresChannelMessageTableSubscriber.class.getName());
+			}
+		}
+		catch (InterruptedException e) {
+			Thread.currentThread().interrupt();
+			throw new IllegalStateException("Failed to start "
+					+ PostgresChannelMessageTableSubscriber.class.getName(), e);
+		}
+	}
+
+	private void notifyAll(Set<Subscription> subscriptions) {
+		subscriptions.forEach(it -> {
+			try {
+				this.executor.submit(it::notifyUpdate);
+			}
+			catch (RejectedExecutionException e) {
+				LOGGER.warn(e, "Executor rejected submission of notification task");
+			}
+		});
 	}
 
 	private boolean isActive() {
@@ -232,6 +264,11 @@ public synchronized void stop() {
 			catch (SQLException ignored) {
 			}
 		}
+
+		if (!this.userProvidedExecutor) {
+			shutdownAndAwaitTermination(this.executor);
+		}
+
 		try {
 			if (!this.latch.await(5, TimeUnit.SECONDS)) {
 				throw new IllegalStateException("Failed to stop "
@@ -242,6 +279,35 @@ public synchronized void stop() {
 		}
 	}
 
+
+	/**
+	 * Gracefully shutdown an executor service. Taken from @see ExecutorService javadoc
+	 *
+	 * @param pool The pool to shut down
+	 */
+	private void shutdownAndAwaitTermination(@Nullable ExecutorService pool) {
+		if (pool == null) {
+			return;
+		}
+		pool.shutdown(); // Disable new tasks from being submitted
+		try {
+			// Wait a while for existing tasks to terminate
+			if (!pool.awaitTermination(2, TimeUnit.SECONDS)) {
+				pool.shutdownNow(); // Cancel currently executing tasks
+				// Wait a while for tasks to respond to being cancelled
+				if (!pool.awaitTermination(2, TimeUnit.SECONDS)) {
+					LOGGER.warn("Unable to shutdown the executor service");
+				}
+			}
+		}
+		catch (InterruptedException ie) {
+			// (Re-)Cancel if current thread also interrupted
+			pool.shutdownNow();
+			// Preserve interrupt status
+			Thread.currentThread().interrupt();
+		}
+	}
+
 	@Override
 	public boolean isRunning() {
 		return this.latch.getCount() > 0;

spring-integration-jdbc/src/main/java/org/springframework/integration/jdbc/channel/PostgresSubscribableChannel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 the original author or authors.
+ * Copyright 2022-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,15 +16,17 @@
 
 package org.springframework.integration.jdbc.channel;
 
-import java.util.concurrent.Executor;
+import java.util.Optional;
 
-import org.springframework.core.task.SimpleAsyncTaskExecutor;
 import org.springframework.integration.channel.AbstractSubscribableChannel;
 import org.springframework.integration.dispatcher.MessageDispatcher;
 import org.springframework.integration.dispatcher.UnicastingDispatcher;
 import org.springframework.integration.jdbc.store.JdbcChannelMessageStore;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageHandler;
+import org.springframework.retry.support.RetryTemplate;
+import org.springframework.transaction.PlatformTransactionManager;
+import org.springframework.transaction.support.TransactionTemplate;
 import org.springframework.util.Assert;
 
 /**
@@ -39,6 +41,7 @@
  *
  * @author Rafael Winterhalter
  * @author Artem Bilan
+ * @author Igor Lovich
  *
  * @since 6.0
  */
@@ -47,11 +50,15 @@ public class PostgresSubscribableChannel extends AbstractSubscribableChannel
 
 	private final JdbcChannelMessageStore jdbcChannelMessageStore;
 
+	private TransactionTemplate transactionTemplate;
+
 	private final Object groupId;
 
 	private final PostgresChannelMessageTableSubscriber messageTableSubscriber;
 
-	private UnicastingDispatcher dispatcher = new UnicastingDispatcher(new SimpleAsyncTaskExecutor());
+	private final UnicastingDispatcher dispatcher = new UnicastingDispatcher();
+
+	private RetryTemplate retryTemplate = RetryTemplate.builder().maxAttempts(1).build();
 
 	/**
 	 * Create a subscribable channel for a Postgres database.
@@ -70,12 +77,22 @@ public PostgresSubscribableChannel(JdbcChannelMessageStore jdbcChannelMessageSto
 	}
 
 	/**
-	 * Set the executor to use for dispatching newly received messages.
-	 * @param executor The executor to use.
+	 * Sets the transaction manager to use for message processing. Each message will be processed in a
+	 * separate transaction
+	 * @param transactionManager The transaction manager to use
 	 */
-	public void setDispatcherExecutor(Executor executor) {
-		Assert.notNull(executor, "An executor must be provided.");
-		this.dispatcher = new UnicastingDispatcher(executor);
+	public void setTransactionManager(PlatformTransactionManager transactionManager) {
+		Assert.notNull(transactionManager, "A platform transaction manager must be provided.");
+		this.transactionTemplate = new TransactionTemplate(transactionManager);
+	}
+
+	/**
+	 * Sets retry template to use for retries in case of exception in downstream processing
+	 * @param retryTemplate The retry template to use
+	 */
+	public void setRetryTemplate(RetryTemplate retryTemplate) {
+		Assert.notNull(retryTemplate, "A retry template must be provided.");
+		this.retryTemplate = retryTemplate;
 	}
 
 	@Override
@@ -110,10 +127,29 @@ protected boolean doSend(Message<?> message, long timeout) {
 
 	@Override
 	public void notifyUpdate() {
-		Message<?> message;
-		while ((message = this.jdbcChannelMessageStore.pollMessageFromGroup(this.groupId)) != null) {
-			this.dispatcher.dispatch(message);
-		}
+		Optional<Message<?>> dispatchedMessage;
+
+		do {
+			if (this.transactionTemplate != null) {
+				dispatchedMessage = this.retryTemplate.execute(context ->
+						this.transactionTemplate.execute(status ->
+								Optional.ofNullable(this.jdbcChannelMessageStore.pollMessageFromGroup(this.groupId))
+										.map(this::dispatch)
+						)
+				);
+			}
+			else {
+				dispatchedMessage = Optional.ofNullable(this.jdbcChannelMessageStore.pollMessageFromGroup(this.groupId))
+						.map(message ->
+								this.retryTemplate.execute(context -> dispatch(message))
+						);
+			}
+		} while (dispatchedMessage.isPresent());
+	}
+
+	private Message<?> dispatch(Message<?> message) {
+		this.dispatcher.dispatch(message);
+		return message;
 	}
 
 	@Override