From 257211fc7a98d62895a6f16f673de7d9a17c5f4a Mon Sep 17 00:00:00 2001
From: SeppPenner <HansM2013@gmx.de>
Date: Thu, 11 Jun 2020 12:41:48 +0200
Subject: [PATCH] Moved undeliveredMessageInterceptor to local variable to
 avoid threading issues.

---
 Source/MQTTnet/Server/MqttClientSessionsManager.cs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Source/MQTTnet/Server/MqttClientSessionsManager.cs b/Source/MQTTnet/Server/MqttClientSessionsManager.cs
index a0f0bf2e..d27a366f 100644
--- a/Source/MQTTnet/Server/MqttClientSessionsManager.cs
+++ b/Source/MQTTnet/Server/MqttClientSessionsManager.cs
@@ -238,12 +238,14 @@ namespace MQTTnet.Server
 
                 if (deliveryCount == 0)
                 {
-                    if (_options.UndeliveredMessageInterceptor == null)
+                    var undeliveredMessageInterceptor = _options.UndeliveredMessageInterceptor;
+
+                    if (undeliveredMessageInterceptor == null)
                     {
                         return;
                     }
 
-                    await _options.UndeliveredMessageInterceptor.InterceptApplicationMessagePublishAsync(new MqttApplicationMessageInterceptorContext(sender?.ClientId, sender?.Session?.Items, applicationMessage));
+                    await undeliveredMessageInterceptor.InterceptApplicationMessagePublishAsync(new MqttApplicationMessageInterceptorContext(sender?.ClientId, sender?.Session?.Items, applicationMessage));
                 }
             }
             catch (OperationCanceledException)