From 579e7cb8ff21e47aa99127686e07ee5b15dd05db Mon Sep 17 00:00:00 2001
From: Mikhail Polivakha <68962645+mipo256@users.noreply.github.com>
Date: Wed, 28 May 2025 19:15:43 +0300
Subject: [PATCH] Altered the example in EmbeddedKafkaHolder usage (#3929)

Integration tests with an EmbeddedKafka instance are sometimes run in parallel in Junit.
The current example is not thread safe, so I think the oficial documentation should account for that.

**Auto-cherry-pick to `3.3.x` & `3.2.x`**

Signed-off-by: mipo256 <mikhailpolivakha@gmail.com>
---
 .../antora/modules/ROOT/pages/testing.adoc    | 23 +++++++++----------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/spring-kafka-docs/src/main/antora/modules/ROOT/pages/testing.adoc b/spring-kafka-docs/src/main/antora/modules/ROOT/pages/testing.adoc
index 5948e41d..9504bf1c 100644
--- a/spring-kafka-docs/src/main/antora/modules/ROOT/pages/testing.adoc
+++ b/spring-kafka-docs/src/main/antora/modules/ROOT/pages/testing.adoc
@@ -162,21 +162,20 @@ public final class EmbeddedKafkaHolder {
 
     public static EmbeddedKafkaBroker getEmbeddedKafka() {
         if (!started) {
-            try {
-                embeddedKafka.afterPropertiesSet();
-            }
-            catch (Exception e) {
-                throw new KafkaException("Embedded broker failed to start", e);
-            }
-            started = true;
+            synchronized (this) {
+		if (!started) {
+		    try {
+	                embeddedKafka.afterPropertiesSet();
+		    }
+	            catch (Exception e) {
+	                throw new KafkaException("Embedded broker failed to start", e);
+		    }
+	            started = true;
+		}
+	    }
         }
         return embeddedKafka;
     }
-
-    private EmbeddedKafkaHolder() {
-        super();
-    }
-
 }
 ----