From 6f8d4c77e6194f8e2b2262d4dc8c22835061c46a Mon Sep 17 00:00:00 2001
From: Andy Wilkinson <awilkinson@pivotal.io>
Date: Wed, 20 Jan 2016 22:23:57 +0000
Subject: [PATCH] Handle multiple ContextRefreshedEvents in
 BackgroundPreinitializer

The same initializer will receive multiple ContextRefreshedEvents
when their is an application context hierarchy. This commit updates
the initializer to correctly handle multiple ContextRefreshedEvents
and only act upon the first that it receives.

See gh-4871
---
 .../BackgroundPreinitializer.java             | 24 +++++++++++--------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/BackgroundPreinitializer.java b/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/BackgroundPreinitializer.java
index 764c2fe9571..0b8bbab11a1 100644
--- a/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/BackgroundPreinitializer.java
+++ b/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/BackgroundPreinitializer.java
@@ -53,7 +53,7 @@ public class BackgroundPreinitializer implements ApplicationListener<Application
 
 	private void performInitialization() {
 		try {
-			this.initializationThread = new Thread(new Runnable() {
+			Thread thread = new Thread(new Runnable() {
 
 				@Override
 				public void run() {
@@ -72,7 +72,8 @@ public class BackgroundPreinitializer implements ApplicationListener<Application
 				}
 
 			}, "background-preinit");
-			this.initializationThread.start();
+			thread.start();
+			this.initializationThread = thread;
 		}
 		catch (Exception ex) {
 			// This will fail on GAE where creating threads is prohibited. We can safely
@@ -82,14 +83,17 @@ public class BackgroundPreinitializer implements ApplicationListener<Application
 	}
 
 	private void awaitInitialization() {
-		try {
-			this.initializationThread.join();
-		}
-		catch (InterruptedException ex) {
-			Thread.currentThread().interrupt();
-		}
-		finally {
-			this.initializationThread = null;
+		Thread thread = this.initializationThread;
+		if (thread != null) {
+			try {
+				thread.join();
+			}
+			catch (InterruptedException ex) {
+				Thread.currentThread().interrupt();
+			}
+			finally {
+				this.initializationThread = null;
+			}
 		}
 	}