Consistent result synchronization in WebAsyncManager

Issue: SPR-16571

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -51,6 +51,7 @@ import org.springframework.web.util.UrlPathHelper;
  * detected via {@link #hasConcurrentResult()}.
  *
  * @author Rossen Stoyanchev
+ * @author Juergen Hoeller
  * @since 3.2
  * @see org.springframework.web.context.request.AsyncWebRequestInterceptor
  * @see org.springframework.web.servlet.AsyncHandlerInterceptor
@@ -76,15 +77,13 @@ public final class WebAsyncManager {
 
 	private AsyncTaskExecutor taskExecutor = new SimpleAsyncTaskExecutor(this.getClass().getSimpleName());
 
-	private Object concurrentResult = RESULT_NONE;
+	private volatile Object concurrentResult = RESULT_NONE;
 
-	private Object[] concurrentResultContext;
+	private volatile Object[] concurrentResultContext;
 
-	private final Map<Object, CallableProcessingInterceptor> callableInterceptors =
-			new LinkedHashMap<>();
+	private final Map<Object, CallableProcessingInterceptor> callableInterceptors = new LinkedHashMap<>();
 
-	private final Map<Object, DeferredResultProcessingInterceptor> deferredResultInterceptors =
-			new LinkedHashMap<>();
+	private final Map<Object, DeferredResultProcessingInterceptor> deferredResultInterceptors = new LinkedHashMap<>();
 
 
 	/**
@@ -105,7 +104,7 @@ public final class WebAsyncManager {
 	 * {@code true}.
 	 * @param asyncWebRequest the web request to use
 	 */
-	public void setAsyncWebRequest(final AsyncWebRequest asyncWebRequest) {
+	public void setAsyncWebRequest(AsyncWebRequest asyncWebRequest) {
 		Assert.notNull(asyncWebRequest, "AsyncWebRequest must not be null");
 		this.asyncWebRequest = asyncWebRequest;
 		this.asyncWebRequest.addCompletionHandler(() -> asyncWebRequest.removeAttribute(
@@ -130,7 +129,7 @@ public final class WebAsyncManager {
 	 * processing of the concurrent result.
 	 */
 	public boolean isConcurrentHandlingStarted() {
-		return ((this.asyncWebRequest != null) && this.asyncWebRequest.isAsyncStarted());
+		return (this.asyncWebRequest != null && this.asyncWebRequest.isAsyncStarted());
 	}
 
 	/**
@@ -232,8 +231,10 @@ public final class WebAsyncManager {
 	 * {@linkplain #getConcurrentResultContext() concurrentResultContext}.
 	 */
 	public void clearConcurrentResult() {
-		this.concurrentResult = RESULT_NONE;
-		this.concurrentResultContext = null;
+		synchronized (WebAsyncManager.this) {
+			this.concurrentResult = RESULT_NONE;
+			this.concurrentResultContext = null;
+		}
 	}
 
 	/**
@@ -334,7 +335,7 @@ public final class WebAsyncManager {
 
 	private void setConcurrentResultAndDispatch(Object result) {
 		synchronized (WebAsyncManager.this) {
-			if (hasConcurrentResult()) {
+			if (this.concurrentResult != RESULT_NONE) {
 				return;
 			}
 			this.concurrentResult = result;
@@ -349,7 +350,6 @@ public final class WebAsyncManager {
 			logger.debug("Concurrent result value [" + this.concurrentResult +
 					"] - dispatching request to resume processing");
 		}
-
 		this.asyncWebRequest.dispatch();
 	}
 
@@ -425,8 +425,10 @@ public final class WebAsyncManager {
 	}
 
 	private void startAsyncProcessing(Object[] processingContext) {
-		clearConcurrentResult();
-		this.concurrentResultContext = processingContext;
+		synchronized (WebAsyncManager.this) {
+			this.concurrentResult = RESULT_NONE;
+			this.concurrentResultContext = processingContext;
+		}
 		this.asyncWebRequest.startAsync();
 
 		if (logger.isDebugEnabled()) {