Polishing

See gh-21798

spring-messaging/src/main/java/org/springframework/messaging/simp/broker/AbstractBrokerMessageHandler.java

@@ -161,8 +161,7 @@ public abstract class AbstractBrokerMessageHandler
 	 * ThreadPoolExecutor that in turn does not guarantee processing in order.
 	 * <p>When this flag is set to {@code true} messages within the same session
 	 * will be sent to the {@code "clientOutboundChannel"} one at a time in
-	 * order to preserve the order of publication. Enable this only if needed
-	 * since there is some performance overhead to keep messages in order.
+	 * order to preserve the order of publication.
 	 * @param preservePublishOrder whether to publish in order
 	 * @since 5.1
 	 */

spring-messaging/src/main/java/org/springframework/messaging/simp/broker/OrderedMessageChannelDecorator.java

@@ -89,11 +89,7 @@ public class OrderedMessageChannelDecorator implements MessageChannel {
 			Message<?> message = this.messages.peek();
 			if (message != null) {
 				try {
-					addNextMessageTaskHeader(message, () -> {
-						if (removeMessage(message)) {
-							sendNextMessage();
-						}
-					});
+					setTaskHeader(message, new PostHandleTask(message));
 					if (this.channel.send(message)) {
 						return;
 					}
@@ -124,19 +120,12 @@ public class OrderedMessageChannelDecorator implements MessageChannel {
 		}
 	}
 
-	private static void addNextMessageTaskHeader(Message<?> message, Runnable task) {
+	private static void setTaskHeader(Message<?> message, Runnable task) {
 		SimpMessageHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message, SimpMessageHeaderAccessor.class);
 		Assert.isTrue(accessor != null && accessor.isMutable(), "Expected mutable SimpMessageHeaderAccessor");
 		accessor.setHeader(NEXT_MESSAGE_TASK_HEADER, task);
 	}
 
-	/**
-	 * Obtain the task to release the next message, if found.
-	 */
-	@Nullable
-	public static Runnable getNextMessageTask(Message<?> message) {
-		return (Runnable) message.getHeaders().get(OrderedMessageChannelDecorator.NEXT_MESSAGE_TASK_HEADER);
-	}
 
 	/**
 	 * Install or remove an {@link ExecutorChannelInterceptor} that invokes a
@@ -150,19 +139,47 @@ public class OrderedMessageChannelDecorator implements MessageChannel {
 			Assert.isInstanceOf(ExecutorSubscribableChannel.class, channel,
 					"An ExecutorSubscribableChannel is required for 'preservePublishOrder'");
 			ExecutorSubscribableChannel execChannel = (ExecutorSubscribableChannel) channel;
-			if (execChannel.getInterceptors().stream().noneMatch(CallbackInterceptor.class::isInstance)) {
-				execChannel.addInterceptor(0, new CallbackInterceptor());
+			if (execChannel.getInterceptors().stream().noneMatch(CallbackTaskInterceptor.class::isInstance)) {
+				execChannel.addInterceptor(0, new CallbackTaskInterceptor());
 			}
 		}
 		else if (channel instanceof ExecutorSubscribableChannel execChannel) {
-			execChannel.getInterceptors().stream().filter(CallbackInterceptor.class::isInstance)
+			execChannel.getInterceptors().stream().filter(CallbackTaskInterceptor.class::isInstance)
 					.findFirst().map(execChannel::removeInterceptor);
 
 		}
 	}
 
+	/**
+	 * Obtain the task to release the next message, if found.
+	 */
+	@Nullable
+	public static Runnable getNextMessageTask(Message<?> message) {
+		return (Runnable) message.getHeaders().get(OrderedMessageChannelDecorator.NEXT_MESSAGE_TASK_HEADER);
+	}
 
-	private static class CallbackInterceptor implements ExecutorChannelInterceptor {
+
+	/**
+	 * Remove handled message from queue, and send next message.
+	 */
+	private class PostHandleTask implements Runnable {
+
+		private final Message<?> message;
+
+		private PostHandleTask(Message<?> message) {
+			this.message = message;
+		}
+
+		@Override
+		public void run() {
+			if (OrderedMessageChannelDecorator.this.removeMessage(message)) {
+				sendNextMessage();
+			}
+		}
+	}
+
+
+	private static class CallbackTaskInterceptor implements ExecutorChannelInterceptor {
 
 		@Override
 		public void afterMessageHandled(

spring-messaging/src/main/java/org/springframework/messaging/simp/config/MessageBrokerRegistry.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -228,8 +228,7 @@ public class MessageBrokerRegistry {
 	 * ThreadPoolExecutor that in turn does not guarantee processing in order.
 	 * <p>When this flag is set to {@code true} messages within the same session
 	 * will be sent to the {@code "clientOutboundChannel"} one at a time in
-	 * order to preserve the order of publication. Enable this only if needed
-	 * since there is some performance overhead to keep messages in order.
+	 * order to preserve the order of publication.
 	 * @since 5.1
 	 */
 	public MessageBrokerRegistry setPreservePublishOrder(boolean preservePublishOrder) {

spring-messaging/src/main/java/org/springframework/messaging/support/AbstractSubscribableChannel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -35,7 +35,7 @@ public abstract class AbstractSubscribableChannel extends AbstractMessageChannel
 
 
 	public Set<MessageHandler> getSubscribers() {
-		return Collections.<MessageHandler>unmodifiableSet(this.handlers);
+		return Collections.unmodifiableSet(this.handlers);
 	}
 
 	public boolean hasSubscription(MessageHandler handler) {