From 224589ea74a2bfd4230e67331c109944df7260b4 Mon Sep 17 00:00:00 2001
From: Rossen Stoyanchev <rstoyanchev@pivotal.io>
Date: Wed, 11 Apr 2018 14:23:16 -0400
Subject: [PATCH] Remove write pausing in Undertow response

Using the simple example shown in the ticket but switching from
Mono<String> to Flux<String> (and 5,000,000 onNext calls) shows that
constant pausing causes significant overhead and is not worth the
trouble vs ignoring the onWritePossible in REQUESTED state.

Issue: SPR-16702
---
 .../http/server/reactive/AbstractListenerWriteProcessor.java | 5 +++++
 .../http/server/reactive/UndertowServerHttpResponse.java     | 5 -----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteProcessor.java b/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteProcessor.java
index bc55d0052b..50a245dc30 100644
--- a/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteProcessor.java
+++ b/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteProcessor.java
@@ -162,7 +162,11 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 	 * Invoked after the current data has been written and before requesting
 	 * the next item from the upstream, write Publisher.
 	 * <p>The default implementation is a no-op.
+	 * @deprecated originally introduced for Undertow to stop write notifications
+	 * when no data is available, but deprecated as of as of 5.0.6 since constant
+	 * switching on every requested item causes a significant slowdown.
 	 */
+	@Deprecated
 	protected void writingPaused() {
 	}
 
@@ -271,6 +275,7 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 		},
 
 		RECEIVED {
+			@SuppressWarnings("deprecation")
 			@Override
 			public <T> void onWritePossible(AbstractListenerWriteProcessor<T> processor) {
 				if (processor.changeState(this, WRITING)) {
diff --git a/spring-web/src/main/java/org/springframework/http/server/reactive/UndertowServerHttpResponse.java b/spring-web/src/main/java/org/springframework/http/server/reactive/UndertowServerHttpResponse.java
index b00e338010..58aed42f29 100644
--- a/spring-web/src/main/java/org/springframework/http/server/reactive/UndertowServerHttpResponse.java
+++ b/spring-web/src/main/java/org/springframework/http/server/reactive/UndertowServerHttpResponse.java
@@ -217,11 +217,6 @@ class UndertowServerHttpResponse extends AbstractListenerServerHttpResponse impl
 			return (dataBuffer.readableByteCount() == 0);
 		}
 
-		@Override
-		protected void writingPaused() {
-			this.channel.suspendWrites();
-		}
-
 		@Override
 		protected void writingComplete() {
 			this.channel.getWriteSetter().set(null);