Synchronized onRefresh execution for concurrent ContextRefreshedEvent

Issue: SPR-17442

spring-webmvc/src/main/java/org/springframework/web/servlet/FrameworkServlet.java

@@ -209,6 +209,9 @@ public abstract class FrameworkServlet extends HttpServletBean implements Applic
 	/** Should we dispatch an HTTP TRACE request to {@link #doService}?. */
 	private boolean dispatchTraceRequest = false;
 
+	/** Whether to log potentially sensitive info (request params at DEBUG + headers at TRACE). */
+	private boolean enableLoggingRequestDetails = false;
+
 	/** WebApplicationContext for this servlet. */
 	@Nullable
 	private WebApplicationContext webApplicationContext;
@@ -217,10 +220,10 @@ public abstract class FrameworkServlet extends HttpServletBean implements Applic
 	private boolean webApplicationContextInjected = false;
 
 	/** Flag used to detect whether onRefresh has already been called. */
-	private boolean refreshEventReceived = false;
+	private volatile boolean refreshEventReceived = false;
 
-	/** Whether to log potentially sensitive info (request params at DEBUG + headers at TRACE). */
-	private boolean enableLoggingRequestDetails = false;
+	/** Monitor for synchronized onRefresh execution. */
+	private final Object onRefreshMonitor = new Object();
 
 
 	/**
@@ -591,7 +594,9 @@ public abstract class FrameworkServlet extends HttpServletBean implements Applic
 			// Either the context is not a ConfigurableApplicationContext with refresh
 			// support or the context injected at construction time had already been
 			// refreshed -> trigger initial onRefresh manually here.
-			onRefresh(wac);
+			synchronized (this.onRefreshMonitor) {
+				onRefresh(wac);
+			}
 		}
 
 		if (this.publishContext) {
@@ -832,7 +837,9 @@ public abstract class FrameworkServlet extends HttpServletBean implements Applic
 	 */
 	public void onApplicationEvent(ContextRefreshedEvent event) {
 		this.refreshEventReceived = true;
-		onRefresh(event.getApplicationContext());
+		synchronized (this.onRefreshMonitor) {
+			onRefresh(event.getApplicationContext());
+		}
 	}
 
 	/**