Shutdown hook triggers doClose within startupShutdownMonitor

Issue: SPR-13556

Author: jhoeller

spring-context/src/main/java/org/springframework/context/support/AbstractApplicationContext.java

@@ -891,7 +891,9 @@ public void registerShutdownHook() {
 			this.shutdownHook = new Thread() {
 				@Override
 				public void run() {
-					doClose();
+					synchronized (startupShutdownMonitor) {
+						doClose();
+					}
 				}
 			};
 			Runtime.getRuntime().addShutdownHook(this.shutdownHook);