Fix ImapIdleChA for scheduling race condition (#8670)

* Fix ImapIdleChA for scheduling race condition

The IMAP IDLE is long-lived process and can be blocked
waiting for any reply from the server.
This way it is not suited to be used in a `TaskScheduler`
especially when it has only one thread in its pool in Spring Boot by default.
Another concurrent scheduled task is exactly an `ImapMailReceiver.IdleCanceller`.
With a single thread in a `TaskScheduler` pool it cannot be reached
therefore we never cancel and IDLE task and cannot react to the connection loss properly

* Rework the `ImapIdleChannelAdapter` logic to use a regular `Executor` and `while()` loop
with a `Thread.sleep()` when we lose connection
* Clean up the `ImapMailReceiverTests` from `TaskScheduler` not used anymore.
* Expose new `taskExecutor` option in the `ImapIdleChannelAdapterSpec` for Java DSL
* Enable `ImapMailReceiverTests.testIdleWithMessageMapping()` with an attempt to see
if this fix covers an unclear problem exposed before

* * The `testIdleWithMessageMapping()` still fails on GH actions

Author: artembilan

spring-integration-mail/src/main/java/org/springframework/integration/mail/ImapIdleChannelAdapter.java

@@ -17,10 +17,9 @@
 package org.springframework.integration.mail;
 
 import java.io.Serial;
-import java.time.Instant;
 import java.util.List;
+import java.util.concurrent.Executor;
 import java.util.concurrent.ScheduledFuture;
-import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Consumer;
 
 import jakarta.mail.Folder;
@@ -31,15 +30,13 @@
 import org.springframework.beans.factory.BeanClassLoaderAware;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.context.ApplicationEventPublisherAware;
+import org.springframework.core.task.SimpleAsyncTaskExecutor;
 import org.springframework.integration.endpoint.MessageProducerSupport;
 import org.springframework.integration.mail.event.MailIntegrationEvent;
 import org.springframework.integration.transaction.IntegrationResourceHolder;
 import org.springframework.integration.transaction.IntegrationResourceHolderSynchronization;
 import org.springframework.integration.transaction.TransactionSynchronizationFactory;
 import org.springframework.messaging.MessagingException;
-import org.springframework.scheduling.TaskScheduler;
-import org.springframework.scheduling.Trigger;
-import org.springframework.scheduling.TriggerContext;
 import org.springframework.transaction.support.TransactionSynchronization;
 import org.springframework.transaction.support.TransactionSynchronizationManager;
 import org.springframework.util.Assert;
@@ -63,12 +60,10 @@ public class ImapIdleChannelAdapter extends MessageProducerSupport implements Be
 
 	private static final int DEFAULT_RECONNECT_DELAY = 10000;
 
-	private final ExceptionAwarePeriodicTrigger receivingTaskTrigger = new ExceptionAwarePeriodicTrigger();
-
-	private final IdleTask idleTask = new IdleTask();
-
 	private final ImapMailReceiver mailReceiver;
 
+	private Executor taskExecutor;
+
 	private TransactionSynchronizationFactory transactionSynchronizationFactory;
 
 	private ClassLoader classLoader;
@@ -100,6 +95,16 @@ public void setAdviceChain(List<Advice> adviceChain) {
 		this.adviceChain = adviceChain;
 	}
 
+	/**
+	 * Provide a managed {@link Executor} to schedule a receiving IDLE task.
+	 * @param taskExecutor the {@link Executor} to use.
+	 * @since 6.2
+	 */
+	public void setTaskExecutor(Executor taskExecutor) {
+		Assert.notNull(taskExecutor, "'taskExecutor' must not be null");
+		this.taskExecutor = taskExecutor;
+	}
+
 	/**
 	 * Specify whether the IDLE task should reconnect automatically after
 	 * catching a {@link jakarta.mail.MessagingException} while waiting for messages. The
@@ -139,6 +144,10 @@ public void setApplicationEventPublisher(ApplicationEventPublisher applicationEv
 	protected void onInit() {
 		super.onInit();
 
+		if (this.taskExecutor == null) {
+			this.taskExecutor = new SimpleAsyncTaskExecutor(getBeanName() + "-");
+		}
+
 		Consumer<?> messageSenderToUse = new MessageSender();
 
 		if (!CollectionUtils.isEmpty(this.adviceChain)) {
@@ -153,16 +162,9 @@ protected void onInit() {
 		this.messageSender = (Consumer<Object>) messageSenderToUse;
 	}
 
-
-	/*
-	 * Lifecycle implementation
-	 */
-
-	@Override // guarded by super#lifecycleLock
+	@Override
 	protected void doStart() {
-		TaskScheduler scheduler = getTaskScheduler();
-		Assert.notNull(scheduler, "'taskScheduler' must not be null");
-		this.receivingTask = scheduler.schedule(new ReceivingTask(), this.receivingTaskTrigger);
+		this.taskExecutor.execute(this::callIdle);
 	}
 
 	@Override
@@ -190,6 +192,70 @@ private void publishException(Exception ex) {
 		}
 	}
 
+	private void callIdle() {
+		while (isActive()) {
+			try {
+				processIdle();
+				logger.debug("Task completed successfully. Re-scheduling it again right away.");
+			}
+			catch (Exception ex) {
+				publishException(ex);
+				if (this.shouldReconnectAutomatically
+						&& ex.getCause() instanceof jakarta.mail.MessagingException messagingException) {
+
+					//run again after a delay
+					logger.info(messagingException,
+							() -> "Failed to execute IDLE task. Will attempt to resubmit in "
+									+ this.reconnectDelay + " milliseconds.");
+					delayNextIdleCall();
+				}
+				else {
+					logger.warn(ex,
+							"Failed to execute IDLE task. " +
+									"Won't resubmit since not a 'shouldReconnectAutomatically' " +
+									"or not a 'jakarta.mail.MessagingException'");
+					break;
+				}
+			}
+		}
+	}
+
+	private void processIdle() {
+		try {
+			logger.debug("waiting for mail");
+			this.mailReceiver.waitForNewMessages();
+			Folder folder = this.mailReceiver.getFolder();
+			if (folder != null && folder.isOpen() && isRunning()) {
+				Object[] mailMessages = this.mailReceiver.receive();
+				logger.debug(() -> "received " + mailMessages.length + " mail messages");
+				for (Object mailMessage : mailMessages) {
+					if (isRunning()) {
+						this.messageSender.accept(mailMessage);
+					}
+				}
+			}
+		}
+		catch (jakarta.mail.MessagingException ex) {
+			logger.warn(ex, "error occurred in idle task");
+			if (this.shouldReconnectAutomatically) {
+				throw new IllegalStateException("Failure in 'idle' task. Will resubmit.", ex);
+			}
+			else {
+				throw new MessagingException("Failure in 'idle' task. Will NOT resubmit.", ex);
+			}
+		}
+	}
+
+	private void delayNextIdleCall() {
+		try {
+			Thread.sleep(this.reconnectDelay);
+		}
+		catch (InterruptedException ex) {
+			Thread.currentThread().interrupt();
+			throw new IllegalStateException(ex);
+		}
+	}
+
 	private class MessageSender implements Consumer<Object> {
 
 		MessageSender() {
@@ -227,112 +293,6 @@ public void accept(Object mailMessage) {
 
 	}
 
-	private class ReceivingTask implements Runnable {
-
-		ReceivingTask() {
-		}
-
-		@Override
-		public void run() {
-			if (isRunning()) {
-				try {
-					ImapIdleChannelAdapter.this.idleTask.run();
-					logger.debug("Task completed successfully. Re-scheduling it again right away.");
-				}
-				catch (Exception ex) {
-					if (ImapIdleChannelAdapter.this.shouldReconnectAutomatically
-							&& ex.getCause() instanceof jakarta.mail.MessagingException messagingException) {
-
-						//run again after a delay
-						logger.info(messagingException,
-								() -> "Failed to execute IDLE task. Will attempt to resubmit in "
-										+ ImapIdleChannelAdapter.this.reconnectDelay + " milliseconds.");
-						ImapIdleChannelAdapter.this.receivingTaskTrigger.delayNextExecution();
-					}
-					else {
-						logger.warn(ex,
-								"Failed to execute IDLE task. " +
-										"Won't resubmit since not a 'shouldReconnectAutomatically' " +
-										"or not a 'jakarta.mail.MessagingException'");
-						ImapIdleChannelAdapter.this.receivingTaskTrigger.stop();
-					}
-					publishException(ex);
-				}
-			}
-		}
-
-	}
-
-
-	private class IdleTask implements Runnable {
-
-		IdleTask() {
-		}
-
-		@Override
-		public void run() {
-			if (isRunning()) {
-				try {
-					logger.debug("waiting for mail");
-					ImapIdleChannelAdapter.this.mailReceiver.waitForNewMessages();
-					Folder folder = ImapIdleChannelAdapter.this.mailReceiver.getFolder();
-					if (folder != null && folder.isOpen() && isRunning()) {
-						Object[] mailMessages = ImapIdleChannelAdapter.this.mailReceiver.receive();
-						logger.debug(() -> "received " + mailMessages.length + " mail messages");
-						for (Object mailMessage : mailMessages) {
-							if (isRunning()) {
-								ImapIdleChannelAdapter.this.messageSender.accept(mailMessage);
-							}
-						}
-					}
-				}
-				catch (jakarta.mail.MessagingException ex) {
-					logger.warn(ex, "error occurred in idle task");
-					if (ImapIdleChannelAdapter.this.shouldReconnectAutomatically) {
-						throw new IllegalStateException("Failure in 'idle' task. Will resubmit.", ex);
-					}
-					else {
-						throw new MessagingException("Failure in 'idle' task. Will NOT resubmit.", ex);
-					}
-				}
-			}
-		}
-
-	}
-
-	private class ExceptionAwarePeriodicTrigger implements Trigger {
-
-		private final AtomicBoolean delayNextExecution = new AtomicBoolean();
-
-		private final AtomicBoolean stop = new AtomicBoolean();
-
-
-		ExceptionAwarePeriodicTrigger() {
-		}
-
-		@Override
-		public Instant nextExecution(TriggerContext triggerContext) {
-			if (this.stop.getAndSet(false)) {
-				return null;
-			}
-			if (this.delayNextExecution.getAndSet(false)) {
-				return Instant.now().plusMillis(ImapIdleChannelAdapter.this.reconnectDelay);
-			}
-			else {
-				return Instant.now();
-			}
-		}
-
-		void delayNextExecution() {
-			this.delayNextExecution.set(true);
-		}
-
-		void stop() {
-			this.stop.set(true);
-		}
-
-	}
-
 	public class ImapIdleExceptionEvent extends MailIntegrationEvent {
 
 		@Serial

spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/ImapIdleChannelAdapterSpec.java

@@ -22,6 +22,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
+import java.util.concurrent.Executor;
 import java.util.function.Consumer;
 import java.util.function.Function;
 
@@ -395,6 +396,17 @@ public ImapIdleChannelAdapterSpec simpleContent(boolean simpleContent) {
 		return _this();
 	}
 
+	/**
+	 * Provide a managed {@link Executor} to schedule a receiving IDLE task.
+	 * @param taskExecutor the {@link Executor} to use.
+	 * @return the spec.
+	 * @since 6.2
+	 */
+	public ImapIdleChannelAdapterSpec taskExecutor(Executor taskExecutor) {
+		this.target.setTaskExecutor(taskExecutor);
+		return this;
+	}
+
 	@Override
 	public Map<Object, String> getComponentsToRegister() {
 		return this.componentsToRegister;

spring-integration-mail/src/test/java/org/springframework/integration/mail/ImapMailReceiverTests.java

@@ -228,7 +228,6 @@ public void testIdleWithServerGuts(ImapMailReceiver receiver, boolean mapped, bo
 		ImapIdleChannelAdapter adapter = new ImapIdleChannelAdapter(receiver);
 		QueueChannel channel = new QueueChannel();
 		adapter.setOutputChannel(channel);
-		adapter.setTaskScheduler(taskScheduler);
 		adapter.setReconnectDelay(10);
 		adapter.afterPropertiesSet();
 		adapter.start();
@@ -781,17 +780,14 @@ public void testConnectionException() throws Exception {
 			theEvent.set(event);
 			latch.countDown();
 		});
-		ThreadPoolTaskScheduler taskScheduler = new ThreadPoolTaskScheduler();
-		taskScheduler.initialize();
-		adapter.setTaskScheduler(taskScheduler);
 		adapter.setReconnectDelay(10);
+		adapter.afterPropertiesSet();
 		adapter.start();
 		assertThat(latch.await(10, TimeUnit.SECONDS)).isTrue();
 		assertThat(theEvent.get().toString())
 				.endsWith("cause=java.lang.IllegalStateException: Failure in 'idle' task. Will resubmit.]");
 
 		adapter.stop();
-		taskScheduler.destroy();
 	}
 
 	@Test // see INT-1801
@@ -967,19 +963,15 @@ public void testIdleReconnects() throws Exception {
 			i.callRealMethod();
 			throw new FolderClosedException(folder, "test");
 		}).given(receiver).waitForNewMessages();
-		ThreadPoolTaskScheduler taskScheduler = new ThreadPoolTaskScheduler();
-		taskScheduler.initialize();
-		adapter.setTaskScheduler(taskScheduler);
 		adapter.setReconnectDelay(10);
-		adapter.afterPropertiesSet();
-		final CountDownLatch latch = new CountDownLatch(3);
+		CountDownLatch latch = new CountDownLatch(3);
 		adapter.setApplicationEventPublisher(e -> latch.countDown());
+		adapter.afterPropertiesSet();
 		adapter.start();
 		assertThat(latch.await(60, TimeUnit.SECONDS)).isTrue();
 		verify(store, atLeast(3)).connect();
 
 		adapter.stop();
-		taskScheduler.shutdown();
 	}
 
 	private void setUpScheduler(ImapMailReceiver mailReceiver, ThreadPoolTaskScheduler taskScheduler) {