Wait for up to 30s for access logs to be written during shutdown

Closes gh-17119

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/UndertowReactiveWebServerFactory.java

@@ -23,6 +23,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
+import java.util.concurrent.TimeUnit;
 
 import io.undertow.Handlers;
 import io.undertow.Undertow;
@@ -156,10 +157,14 @@ public class UndertowReactiveWebServerFactory extends AbstractReactiveWebServerF
 				try {
 					accessLogReceiver.close();
 					worker.shutdown();
+					worker.awaitTermination(30, TimeUnit.SECONDS);
 				}
 				catch (IOException ex) {
 					throw new IllegalStateException(ex);
 				}
+				catch (InterruptedException ex) {
+					Thread.currentThread().interrupt();
+				}
 			};
 		}
 		catch (IOException ex) {

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/UndertowServletWebServerFactory.java

@@ -28,6 +28,7 @@ import java.util.Collections;
 import java.util.EventListener;
 import java.util.List;
 import java.util.Set;
+import java.util.concurrent.TimeUnit;
 
 import javax.servlet.ServletContainerInitializer;
 import javax.servlet.ServletContext;
@@ -652,10 +653,14 @@ public class UndertowServletWebServerFactory extends AbstractServletWebServerFac
 			try {
 				this.accessLogReceiver.close();
 				this.worker.shutdown();
+				this.worker.awaitTermination(30, TimeUnit.SECONDS);
 			}
 			catch (IOException ex) {
 				throw new IllegalStateException(ex);
 			}
+			catch (InterruptedException ex) {
+				Thread.currentThread().interrupt();
+			}
 		}
 
 	}