From dbb816c6cb1b2c00142df46700b94910d7701b0d Mon Sep 17 00:00:00 2001
From: kske <kai@kske.dev>
Date: Thu, 24 Sep 2020 17:41:08 +0200
Subject: [PATCH] Add double checked synchronization to EventBus instance
 initializer

---
 src/main/java/dev/kske/eventbus/EventBus.java | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/main/java/dev/kske/eventbus/EventBus.java b/src/main/java/dev/kske/eventbus/EventBus.java
index 4905889..98114fc 100644
--- a/src/main/java/dev/kske/eventbus/EventBus.java
+++ b/src/main/java/dev/kske/eventbus/EventBus.java
@@ -19,7 +19,7 @@ import java.util.concurrent.ConcurrentHashMap;
  */
 public final class EventBus {
 
-	private static EventBus singletonInstance;
+	private static volatile EventBus singletonInstance;
 
 	private static final Logger logger = System.getLogger(EventBus.class.getName());
 
@@ -30,11 +30,15 @@ public final class EventBus {
 	 * @since 0.0.2
 	 */
 	public static EventBus getInstance() {
-		if (singletonInstance == null) {
-			logger.log(Level.DEBUG, "Initializing singleton event bus instance");
-			singletonInstance = new EventBus();
-		}
-		return singletonInstance;
+		EventBus instance = singletonInstance;
+		if (instance == null)
+			synchronized (EventBus.class) {
+				if ((instance = singletonInstance) == null) {
+					logger.log(Level.DEBUG, "Initializing singleton event bus instance");
+					instance = singletonInstance = new EventBus();
+				}
+			}
+		return instance;
 	}
 
 	private final Map<Class<? extends IEvent>, TreeSet<EventHandler>> bindings