Merge branch '6.1.x'

spring-web/src/main/java/org/springframework/web/context/request/async/AsyncRequestNotUsableException.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2002-2024 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://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.springframework.web.context.request.async;
+
+import java.io.IOException;
+
+/**
+ * Raised when the response for an asynchronous request becomes unusable as
+ * indicated by a write failure, or a Servlet container error notification, or
+ * after the async request has completed.
+ *
+ * <p>The exception relies on response wrapping, and on {@code AsyncListener}
+ * notifications, managed by {@link StandardServletAsyncWebRequest}.
+ *
+ * @author Rossen Stoyanchev
+ * @since 5.3.33
+ */
+@SuppressWarnings("serial")
+public class AsyncRequestNotUsableException extends IOException {
+
+
+	public AsyncRequestNotUsableException(String message) {
+		super(message);
+	}
+
+	public AsyncRequestNotUsableException(String message, Throwable cause) {
+		super(message, cause);
+	}
+
+}

spring-web/src/main/java/org/springframework/web/context/request/async/StandardServletAsyncWebRequest.java

@@ -17,16 +17,22 @@
 package org.springframework.web.context.request.async;
 
 import java.io.IOException;
+import java.io.PrintWriter;
 import java.util.ArrayList;
 import java.util.List;
-import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.Locale;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.function.Consumer;
 
 import jakarta.servlet.AsyncContext;
 import jakarta.servlet.AsyncEvent;
 import jakarta.servlet.AsyncListener;
+import jakarta.servlet.ServletOutputStream;
+import jakarta.servlet.WriteListener;
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.servlet.http.HttpServletResponse;
+import jakarta.servlet.http.HttpServletResponseWrapper;
 
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
@@ -45,8 +51,6 @@ import org.springframework.web.context.request.ServletWebRequest;
  */
 public class StandardServletAsyncWebRequest extends ServletWebRequest implements AsyncWebRequest, AsyncListener {
 
-	private final AtomicBoolean asyncCompleted = new AtomicBoolean();
-
 	private final List<Runnable> timeoutHandlers = new ArrayList<>();
 
 	private final List<Consumer<Throwable>> exceptionHandlers = new ArrayList<>();
@@ -59,6 +63,10 @@ public class StandardServletAsyncWebRequest extends ServletWebRequest implements
 	@Nullable
 	private AsyncContext asyncContext;
 
+	private State state;
+
+	private final ReentrantLock stateLock = new ReentrantLock();
+
 
 	/**
 	 * Create a new instance for the given request/response pair.
@@ -66,7 +74,26 @@ public class StandardServletAsyncWebRequest extends ServletWebRequest implements
 	 * @param response current HTTP response
 	 */
 	public StandardServletAsyncWebRequest(HttpServletRequest request, HttpServletResponse response) {
-		super(request, response);
+		this(request, response, null);
+	}
+
+	/**
+	 * Constructor to wrap the request and response for the current dispatch that
+	 * also picks up the state of the last (probably the REQUEST) dispatch.
+	 * @param request current HTTP request
+	 * @param response current HTTP response
+	 * @param previousRequest the existing request from the last dispatch
+	 * @since 5.3.33
+	 */
+	StandardServletAsyncWebRequest(HttpServletRequest request, HttpServletResponse response,
+			@Nullable StandardServletAsyncWebRequest previousRequest) {
+
+		super(request, new LifecycleHttpServletResponse(response));
+
+		this.state = (previousRequest != null ? previousRequest.state : State.NEW);
+
+		//noinspection DataFlowIssue
+		((LifecycleHttpServletResponse) getResponse()).setAsyncWebRequest(this);
 	}
 
 
@@ -107,7 +134,7 @@ public class StandardServletAsyncWebRequest extends ServletWebRequest implements
 	 */
 	@Override
 	public boolean isAsyncComplete() {
-		return this.asyncCompleted.get();
+		return (this.state == State.COMPLETED);
 	}
 
 	@Override
@@ -117,11 +144,18 @@ public class StandardServletAsyncWebRequest extends ServletWebRequest implements
 				"in async request processing. This is done in Java code using the Servlet API " +
 				"or by adding \"<async-supported>true</async-supported>\" to servlet and " +
 				"filter declarations in web.xml.");
-		Assert.state(!isAsyncComplete(), "Async processing has already completed");
 
 		if (isAsyncStarted()) {
 			return;
 		}
+
+		if (this.state == State.NEW) {
+			this.state = State.ASYNC;
+		}
+		else {
+			Assert.state(this.state == State.ASYNC, "Cannot start async: [" + this.state + "]");
+		}
+
 		this.asyncContext = getRequest().startAsync(getRequest(), getResponse());
 		this.asyncContext.addListener(this);
 		if (this.timeout != null) {
@@ -131,8 +165,10 @@ public class StandardServletAsyncWebRequest extends ServletWebRequest implements
 
 	@Override
 	public void dispatch() {
-		Assert.state(this.asyncContext != null, "Cannot dispatch without an AsyncContext");
-		this.asyncContext.dispatch();
+		Assert.state(this.asyncContext != null, "AsyncContext not yet initialized");
+		if (!this.isAsyncComplete()) {
+			this.asyncContext.dispatch();
+		}
 	}
 
 
@@ -151,14 +187,478 @@ public class StandardServletAsyncWebRequest extends ServletWebRequest implements
 
 	@Override
 	public void onError(AsyncEvent event) throws IOException {
-		this.exceptionHandlers.forEach(consumer -> consumer.accept(event.getThrowable()));
+		this.stateLock.lock();
+		try {
+			transitionToErrorState();
+			Throwable ex = event.getThrowable();
+			this.exceptionHandlers.forEach(consumer -> consumer.accept(ex));
+		}
+		finally {
+			this.stateLock.unlock();
+		}
+	}
+
+	private void transitionToErrorState() {
+		if (!isAsyncComplete()) {
+			this.state = State.ERROR;
+		}
 	}
 
 	@Override
 	public void onComplete(AsyncEvent event) throws IOException {
-		this.completionHandlers.forEach(Runnable::run);
-		this.asyncContext = null;
-		this.asyncCompleted.set(true);
+		this.stateLock.lock();
+		try {
+			this.completionHandlers.forEach(Runnable::run);
+			this.asyncContext = null;
+			this.state = State.COMPLETED;
+		}
+		finally {
+			this.stateLock.unlock();
+		}
+	}
+
+
+	/**
+	 * Response wrapper to wrap the output stream with {@link LifecycleServletOutputStream}.
+	 */
+	private static final class LifecycleHttpServletResponse extends HttpServletResponseWrapper {
+
+		@Nullable
+		private StandardServletAsyncWebRequest asyncWebRequest;
+
+		@Nullable
+		private ServletOutputStream outputStream;
+
+		@Nullable
+		private PrintWriter writer;
+
+		public LifecycleHttpServletResponse(HttpServletResponse response) {
+			super(response);
+		}
+
+		public void setAsyncWebRequest(StandardServletAsyncWebRequest asyncWebRequest) {
+			this.asyncWebRequest = asyncWebRequest;
+		}
+
+		@Override
+		public ServletOutputStream getOutputStream() {
+			if (this.outputStream == null) {
+				Assert.notNull(this.asyncWebRequest, "Not initialized");
+				this.outputStream = new LifecycleServletOutputStream(
+						(HttpServletResponse) getResponse(), this.asyncWebRequest);
+			}
+			return this.outputStream;
+		}
+
+		@Override
+		public PrintWriter getWriter() throws IOException {
+			if (this.writer == null) {
+				Assert.notNull(this.asyncWebRequest, "Not initialized");
+				this.writer = new LifecyclePrintWriter(getResponse().getWriter(), this.asyncWebRequest);
+			}
+			return this.writer;
+		}
+	}
+
+
+	/**
+	 * Wraps a ServletOutputStream to prevent use after Servlet container onError
+	 * notifications, and after async request completion.
+	 */
+	private static final class LifecycleServletOutputStream extends ServletOutputStream {
+
+		private final HttpServletResponse delegate;
+
+		private final StandardServletAsyncWebRequest asyncWebRequest;
+
+		private LifecycleServletOutputStream(
+				HttpServletResponse delegate, StandardServletAsyncWebRequest asyncWebRequest) {
+
+			this.delegate = delegate;
+			this.asyncWebRequest = asyncWebRequest;
+		}
+
+		@Override
+		public boolean isReady() {
+			return false;
+		}
+
+		@Override
+		public void setWriteListener(WriteListener writeListener) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void write(int b) throws IOException {
+			obtainLockAndCheckState();
+			try {
+				this.delegate.getOutputStream().write(b);
+			}
+			catch (IOException ex) {
+				handleIOException(ex, "ServletOutputStream failed to write");
+			}
+			finally {
+				releaseLock();
+			}
+		}
+
+		public void write(byte[] buf, int offset, int len) throws IOException {
+			obtainLockAndCheckState();
+			try {
+				this.delegate.getOutputStream().write(buf, offset, len);
+			}
+			catch (IOException ex) {
+				handleIOException(ex, "ServletOutputStream failed to write");
+			}
+			finally {
+				releaseLock();
+			}
+		}
+
+		@Override
+		public void flush() throws IOException {
+			obtainLockAndCheckState();
+			try {
+				this.delegate.getOutputStream().flush();
+			}
+			catch (IOException ex) {
+				handleIOException(ex, "ServletOutputStream failed to flush");
+			}
+			finally {
+				releaseLock();
+			}
+		}
+
+		@Override
+		public void close() throws IOException {
+			obtainLockAndCheckState();
+			try {
+				this.delegate.getOutputStream().close();
+			}
+			catch (IOException ex) {
+				handleIOException(ex, "ServletOutputStream failed to close");
+			}
+			finally {
+				releaseLock();
+			}
+		}
+
+		private void obtainLockAndCheckState() throws AsyncRequestNotUsableException {
+			if (state() != State.NEW) {
+				stateLock().lock();
+				if (state() != State.ASYNC) {
+					stateLock().unlock();
+					throw new AsyncRequestNotUsableException("Response not usable after " +
+							(state() == State.COMPLETED ?
+									"async request completion" : "onError notification") + ".");
+				}
+			}
+		}
+
+		private void handleIOException(IOException ex, String msg) throws AsyncRequestNotUsableException {
+			this.asyncWebRequest.transitionToErrorState();
+			throw new AsyncRequestNotUsableException(msg, ex);
+		}
+
+		private void releaseLock() {
+			if (state() != State.NEW) {
+				stateLock().unlock();
+			}
+		}
+
+		private State state() {
+			return this.asyncWebRequest.state;
+		}
+
+		private Lock stateLock() {
+			return this.asyncWebRequest.stateLock;
+		}
+
+	}
+
+
+	/**
+	 * Wraps a PrintWriter to prevent use after Servlet container onError
+	 * notifications, and after async request completion.
+	 */
+	private static final class LifecyclePrintWriter extends PrintWriter {
+
+		private final PrintWriter delegate;
+
+		private final StandardServletAsyncWebRequest asyncWebRequest;
+
+		private LifecyclePrintWriter(PrintWriter delegate, StandardServletAsyncWebRequest asyncWebRequest) {
+			super(delegate);
+			this.delegate = delegate;
+			this.asyncWebRequest = asyncWebRequest;
+		}
+
+		@Override
+		public void flush() {
+			if (tryObtainLockAndCheckState()) {
+				try {
+					this.delegate.flush();
+				}
+				finally {
+					releaseLock();
+				}
+			}
+		}
+
+		@Override
+		public void close() {
+			if (tryObtainLockAndCheckState()) {
+				try {
+					this.delegate.close();
+				}
+				finally {
+					releaseLock();
+				}
+			}
+		}
+
+		@Override
+		public boolean checkError() {
+			return this.delegate.checkError();
+		}
+
+		@Override
+		public void write(int c) {
+			if (tryObtainLockAndCheckState()) {
+				try {
+					this.delegate.write(c);
+				}
+				finally {
+					releaseLock();
+				}
+			}
+		}
+
+		@Override
+		public void write(char[] buf, int off, int len) {
+			if (tryObtainLockAndCheckState()) {
+				try {
+					this.delegate.write(buf, off, len);
+				}
+				finally {
+					releaseLock();
+				}
+			}
+		}
+
+		@Override
+		public void write(char[] buf) {
+			this.delegate.write(buf);
+		}
+
+		@Override
+		public void write(String s, int off, int len) {
+			if (tryObtainLockAndCheckState()) {
+				try {
+					this.delegate.write(s, off, len);
+				}
+				finally {
+					releaseLock();
+				}
+			}
+		}
+
+		@Override
+		public void write(String s) {
+			this.delegate.write(s);
+		}
+
+		private boolean tryObtainLockAndCheckState() {
+			if (state() == State.NEW) {
+				return true;
+			}
+			if (stateLock().tryLock()) {
+				if (state() == State.ASYNC) {
+					return true;
+				}
+				stateLock().unlock();
+			}
+			return false;
+		}
+
+		private void releaseLock() {
+			if (state() != State.NEW) {
+				stateLock().unlock();
+			}
+		}
+
+		private State state() {
+			return this.asyncWebRequest.state;
+		}
+
+		private Lock stateLock() {
+			return this.asyncWebRequest.stateLock;
+		}
+
+		// Plain delegates
+
+		@Override
+		public void print(boolean b) {
+			this.delegate.print(b);
+		}
+
+		@Override
+		public void print(char c) {
+			this.delegate.print(c);
+		}
+
+		@Override
+		public void print(int i) {
+			this.delegate.print(i);
+		}
+
+		@Override
+		public void print(long l) {
+			this.delegate.print(l);
+		}
+
+		@Override
+		public void print(float f) {
+			this.delegate.print(f);
+		}
+
+		@Override
+		public void print(double d) {
+			this.delegate.print(d);
+		}
+
+		@Override
+		public void print(char[] s) {
+			this.delegate.print(s);
+		}
+
+		@Override
+		public void print(String s) {
+			this.delegate.print(s);
+		}
+
+		@Override
+		public void print(Object obj) {
+			this.delegate.print(obj);
+		}
+
+		@Override
+		public void println() {
+			this.delegate.println();
+		}
+
+		@Override
+		public void println(boolean x) {
+			this.delegate.println(x);
+		}
+
+		@Override
+		public void println(char x) {
+			this.delegate.println(x);
+		}
+
+		@Override
+		public void println(int x) {
+			this.delegate.println(x);
+		}
+
+		@Override
+		public void println(long x) {
+			this.delegate.println(x);
+		}
+
+		@Override
+		public void println(float x) {
+			this.delegate.println(x);
+		}
+
+		@Override
+		public void println(double x) {
+			this.delegate.println(x);
+		}
+
+		@Override
+		public void println(char[] x) {
+			this.delegate.println(x);
+		}
+
+		@Override
+		public void println(String x) {
+			this.delegate.println(x);
+		}
+
+		@Override
+		public void println(Object x) {
+			this.delegate.println(x);
+		}
+
+		@Override
+		public PrintWriter printf(String format, Object... args) {
+			return this.delegate.printf(format, args);
+		}
+
+		@Override
+		public PrintWriter printf(Locale l, String format, Object... args) {
+			return this.delegate.printf(l, format, args);
+		}
+
+		@Override
+		public PrintWriter format(String format, Object... args) {
+			return this.delegate.format(format, args);
+		}
+
+		@Override
+		public PrintWriter format(Locale l, String format, Object... args) {
+			return this.delegate.format(l, format, args);
+		}
+
+		@Override
+		public PrintWriter append(CharSequence csq) {
+			return this.delegate.append(csq);
+		}
+
+		@Override
+		public PrintWriter append(CharSequence csq, int start, int end) {
+			return this.delegate.append(csq, start, end);
+		}
+
+		@Override
+		public PrintWriter append(char c) {
+			return this.delegate.append(c);
+		}
+	}
+
+
+	/**
+	 * Represents a state for {@link StandardServletAsyncWebRequest} to be in.
+	 * <p><pre>
+	 *        NEW
+	 *         |
+	 *         v
+	 *       ASYNC----> +
+	 *         |        |
+	 *         v        |
+	 *       ERROR      |
+	 *         |        |
+	 *         v        |
+	 *     COMPLETED <--+
+	 * </pre>
+	 * @since 5.3.33
+	 */
+	private enum State {
+
+		/** New request (thas may not do async handling). */
+		NEW,
+
+		/** Async handling has started. */
+		ASYNC,
+
+		/** onError notification received, or ServletOutputStream failed. */
+		ERROR,
+
+		/** onComplete notification received. */
+		COMPLETED
+
 	}
 
 }

spring-web/src/main/java/org/springframework/web/context/request/async/WebAsyncManager.java

@@ -22,6 +22,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.concurrent.Callable;
 import java.util.concurrent.Future;
+import java.util.concurrent.atomic.AtomicReference;
 
 import jakarta.servlet.http.HttpServletRequest;
 import org.apache.commons.logging.Log;
@@ -33,7 +34,6 @@ import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.web.context.request.RequestAttributes;
 import org.springframework.web.context.request.async.DeferredResult.DeferredResultHandler;
-import org.springframework.web.util.DisconnectedClientHelper;
 
 /**
  * The central class for managing asynchronous request processing, mainly intended
@@ -67,16 +67,6 @@ public final class WebAsyncManager {
 
 	private static final Log logger = LogFactory.getLog(WebAsyncManager.class);
 
-	/**
-	 * Log category to use for network failure after a client has gone away.
-	 * @see DisconnectedClientHelper
-	 */
-	private static final String DISCONNECTED_CLIENT_LOG_CATEGORY =
-			"org.springframework.web.server.DisconnectedClient";
-
-	private static final DisconnectedClientHelper disconnectedClientHelper =
-			new DisconnectedClientHelper(DISCONNECTED_CLIENT_LOG_CATEGORY);
-
 	private static final CallableProcessingInterceptor timeoutCallableInterceptor =
 			new TimeoutCallableProcessingInterceptor();
 
@@ -95,12 +85,7 @@ public final class WebAsyncManager {
 	@Nullable
 	private volatile Object[] concurrentResultContext;
 
-	/*
-	 * Whether the concurrentResult is an error. If such errors remain unhandled, some
-	 * Servlet containers will call AsyncListener#onError at the end, after the ASYNC
-	 * and/or the ERROR dispatch (Boot's case), and we need to ignore those.
-	 */
-	private volatile boolean errorHandlingInProgress;
+	private final AtomicReference<State> state = new AtomicReference<>(State.NOT_STARTED);
 
 	private final Map<Object, CallableProcessingInterceptor> callableInterceptors = new LinkedHashMap<>();
 
@@ -132,6 +117,15 @@ public final class WebAsyncManager {
 				WebAsyncUtils.WEB_ASYNC_MANAGER_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST));
 	}
 
+	/**
+	 * Return the current {@link AsyncWebRequest}.
+	 * @since 5.3.33
+	 */
+	@Nullable
+	public AsyncWebRequest getAsyncWebRequest() {
+		return this.asyncWebRequest;
+	}
+
 	/**
 	 * Configure an AsyncTaskExecutor for use with concurrent processing via
 	 * {@link #startCallableProcessing(Callable, Object...)}.
@@ -253,6 +247,12 @@ public final class WebAsyncManager {
 	 * {@linkplain #getConcurrentResultContext() concurrentResultContext}.
 	 */
 	public void clearConcurrentResult() {
+		if (!this.state.compareAndSet(State.RESULT_SET, State.NOT_STARTED)) {
+			if (logger.isDebugEnabled()) {
+				logger.debug("Unexpected call to clear: [" + this.state.get() + "]");
+			}
+			return;
+		}
 		synchronized (WebAsyncManager.this) {
 			this.concurrentResult = RESULT_NONE;
 			this.concurrentResultContext = null;
@@ -293,6 +293,11 @@ public final class WebAsyncManager {
 		Assert.notNull(webAsyncTask, "WebAsyncTask must not be null");
 		Assert.state(this.asyncWebRequest != null, "AsyncWebRequest must not be null");
 
+		if (!this.state.compareAndSet(State.NOT_STARTED, State.ASYNC_PROCESSING)) {
+			throw new IllegalStateException(
+					"Unexpected call to startCallableProcessing: [" + this.state.get() + "]");
+		}
+
 		Long timeout = webAsyncTask.getTimeout();
 		if (timeout != null) {
 			this.asyncWebRequest.setTimeout(timeout);
@@ -313,7 +318,7 @@ public final class WebAsyncManager {
 
 		this.asyncWebRequest.addTimeoutHandler(() -> {
 			if (logger.isDebugEnabled()) {
-				logger.debug("Async request timeout for " + formatUri(this.asyncWebRequest));
+				logger.debug("Servlet container timeout notification for " + formatUri(this.asyncWebRequest));
 			}
 			Object result = interceptorChain.triggerAfterTimeout(this.asyncWebRequest, callable);
 			if (result != CallableProcessingInterceptor.RESULT_NONE) {
@@ -322,14 +327,12 @@ public final class WebAsyncManager {
 		});
 
 		this.asyncWebRequest.addErrorHandler(ex -> {
-			if (!this.errorHandlingInProgress) {
-				if (logger.isDebugEnabled()) {
-					logger.debug("Async request error for " + formatUri(this.asyncWebRequest) + ": " + ex);
-				}
-				Object result = interceptorChain.triggerAfterError(this.asyncWebRequest, callable, ex);
-				result = (result != CallableProcessingInterceptor.RESULT_NONE ? result : ex);
-				setConcurrentResultAndDispatch(result);
+			if (logger.isDebugEnabled()) {
+				logger.debug("Servlet container error notification for " + formatUri(this.asyncWebRequest) + ": " + ex);
 			}
+			Object result = interceptorChain.triggerAfterError(this.asyncWebRequest, callable, ex);
+			result = (result != CallableProcessingInterceptor.RESULT_NONE ? result : ex);
+			setConcurrentResultAndDispatch(result);
 		});
 
 		this.asyncWebRequest.addCompletionHandler(() ->
@@ -361,31 +364,34 @@ public final class WebAsyncManager {
 	}
 
 	private void setConcurrentResultAndDispatch(@Nullable Object result) {
+		Assert.state(this.asyncWebRequest != null, "AsyncWebRequest must not be null");
 		synchronized (WebAsyncManager.this) {
-			if (this.concurrentResult != RESULT_NONE) {
+			if (!this.state.compareAndSet(State.ASYNC_PROCESSING, State.RESULT_SET)) {
+				if (logger.isDebugEnabled()) {
+					logger.debug("Async result already set: " +
+							"[" + this.state.get() + "], ignored result: " + result +
+							" for " + formatUri(this.asyncWebRequest));
+				}
 				return;
 			}
+
 			this.concurrentResult = result;
-			this.errorHandlingInProgress = (result instanceof Throwable);
-		}
-
-		Assert.state(this.asyncWebRequest != null, "AsyncWebRequest must not be null");
-		if (this.asyncWebRequest.isAsyncComplete()) {
 			if (logger.isDebugEnabled()) {
-				logger.debug("Async result set but request already complete: " + formatUri(this.asyncWebRequest));
+				logger.debug("Async result set to: " + result + " for " + formatUri(this.asyncWebRequest));
 			}
-			return;
-		}
 
-		if (result instanceof Exception ex && disconnectedClientHelper.checkAndLogClientDisconnectedException(ex)) {
-			return;
-		}
+			if (this.asyncWebRequest.isAsyncComplete()) {
+				if (logger.isDebugEnabled()) {
+					logger.debug("Async request already completed for " + formatUri(this.asyncWebRequest));
+				}
+				return;
+			}
 
-		if (logger.isDebugEnabled()) {
-			logger.debug("Async " + (this.errorHandlingInProgress ? "error" : "result set") +
-					", dispatch to " + formatUri(this.asyncWebRequest));
+			if (logger.isDebugEnabled()) {
+				logger.debug("Performing async dispatch for " + formatUri(this.asyncWebRequest));
+			}
+			this.asyncWebRequest.dispatch();
 		}
-		this.asyncWebRequest.dispatch();
 	}
 
 	/**
@@ -408,6 +414,11 @@ public final class WebAsyncManager {
 		Assert.notNull(deferredResult, "DeferredResult must not be null");
 		Assert.state(this.asyncWebRequest != null, "AsyncWebRequest must not be null");
 
+		if (!this.state.compareAndSet(State.NOT_STARTED, State.ASYNC_PROCESSING)) {
+			throw new IllegalStateException(
+					"Unexpected call to startDeferredResultProcessing: [" + this.state.get() + "]");
+		}
+
 		Long timeout = deferredResult.getTimeoutValue();
 		if (timeout != null) {
 			this.asyncWebRequest.setTimeout(timeout);
@@ -421,6 +432,9 @@ public final class WebAsyncManager {
 		final DeferredResultInterceptorChain interceptorChain = new DeferredResultInterceptorChain(interceptors);
 
 		this.asyncWebRequest.addTimeoutHandler(() -> {
+			if (logger.isDebugEnabled()) {
+				logger.debug("Servlet container timeout notification for " + formatUri(this.asyncWebRequest));
+			}
 			try {
 				interceptorChain.triggerAfterTimeout(this.asyncWebRequest, deferredResult);
 			}
@@ -430,16 +444,17 @@ public final class WebAsyncManager {
 		});
 
 		this.asyncWebRequest.addErrorHandler(ex -> {
-			if (!this.errorHandlingInProgress) {
-				try {
-					if (!interceptorChain.triggerAfterError(this.asyncWebRequest, deferredResult, ex)) {
-						return;
-					}
-					deferredResult.setErrorResult(ex);
-				}
-				catch (Throwable interceptorEx) {
-					setConcurrentResultAndDispatch(interceptorEx);
+			if (logger.isDebugEnabled()) {
+				logger.debug("Servlet container error notification for " + formatUri(this.asyncWebRequest));
+			}
+			try {
+				if (!interceptorChain.triggerAfterError(this.asyncWebRequest, deferredResult, ex)) {
+					return;
 				}
+				deferredResult.setErrorResult(ex);
+			}
+			catch (Throwable interceptorEx) {
+				setConcurrentResultAndDispatch(interceptorEx);
 			}
 		});
 
@@ -465,10 +480,13 @@ public final class WebAsyncManager {
 		synchronized (WebAsyncManager.this) {
 			this.concurrentResult = RESULT_NONE;
 			this.concurrentResultContext = processingContext;
-			this.errorHandlingInProgress = false;
 		}
 
 		Assert.state(this.asyncWebRequest != null, "AsyncWebRequest must not be null");
+		if (logger.isDebugEnabled()) {
+			logger.debug("Started async request for " + formatUri(this.asyncWebRequest));
+		}
+
 		this.asyncWebRequest.startAsync();
 		if (logger.isDebugEnabled()) {
 			logger.debug("Started async request");
@@ -480,4 +498,31 @@ public final class WebAsyncManager {
 		return (request != null ? request.getRequestURI() : "servlet container");
 	}
 
+
+	/**
+	 * Represents a state for {@link WebAsyncManager} to be in.
+	 * <p><pre>
+	 *        NOT_STARTED <------+
+	 *             |             |
+	 *             v             |
+	 *      ASYNC_PROCESSING     |
+	 *             |             |
+	 *             v             |
+	 *         RESULT_SET -------+
+	 * </pre>
+	 * @since 5.3.33
+	 */
+	private enum State {
+
+		/** No async processing in progress. */
+		NOT_STARTED,
+
+		/** Async handling has started, but the result hasn't been set yet. */
+		ASYNC_PROCESSING,
+
+		/** The result is set, and an async dispatch was performed, unless there is a network error. */
+		RESULT_SET
+
+	}
+
 }

spring-web/src/main/java/org/springframework/web/context/request/async/WebAsyncUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -82,7 +82,10 @@ public abstract class WebAsyncUtils {
 	 * @return an AsyncWebRequest instance (never {@code null})
 	 */
 	public static AsyncWebRequest createAsyncWebRequest(HttpServletRequest request, HttpServletResponse response) {
-		return new StandardServletAsyncWebRequest(request, response);
+		AsyncWebRequest prev = getAsyncManager(request).getAsyncWebRequest();
+		return (prev instanceof StandardServletAsyncWebRequest standardRequest ?
+				new StandardServletAsyncWebRequest(request, response, standardRequest) :
+				new StandardServletAsyncWebRequest(request, response));
 	}
 
 }