From 2bd43d95ced69eec3a7bed86f3d1de27b1dfbb39 Mon Sep 17 00:00:00 2001
From: "Roger A. Light" <roger@atchoo.org>
Date: Fri, 13 Feb 2026 08:31:20 +0000
Subject: [PATCH] Fix mosquitto_loop_start() leaving the mosq stuct in an
 invalid state

This occurs if thread creation fails.

Closes #3496. Thanks to ehoffman2.
---
 ChangeLog.txt     | 6 +++++-
 lib/thread_mosq.c | 2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/ChangeLog.txt b/ChangeLog.txt
index 4cbce699..81810172 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -1,4 +1,4 @@
-2.0.23 - 2026-01-14
+2.0.23 - 2026-xx-xx
 ===================
 
 Broker:
@@ -14,6 +14,10 @@ Broker:
   mosquitto 1.5 or earlier is loaded. Closes #3439.
 - Limit auto_id_prefix to 50 characters. Closes #3440.
 
+Library:
+- Fix mosquitto_loop_start() leaving the mosq stuct in an invalid state if
+  thread creation fails. Closes #3496.
+
 Windows:
 - Installer will not overwrite an existing mosquitto.conf
 
diff --git a/lib/thread_mosq.c b/lib/thread_mosq.c
index cd3a614a..fd593a36 100644
--- a/lib/thread_mosq.c
+++ b/lib/thread_mosq.c
@@ -41,7 +41,6 @@ int mosquitto_loop_start(struct mosquitto *mosq)
 #if defined(WITH_THREADING)
 	if(!mosq || mosq->threaded != mosq_ts_none) return MOSQ_ERR_INVAL;
 
-	mosq->threaded = mosq_ts_self;
 	if(!COMPAT_pthread_create(&mosq->thread_id, NULL, mosquitto__thread_main, mosq)){
 #if defined(__linux__)
 		pthread_setname_np(mosq->thread_id, "mosquitto loop");
@@ -50,6 +49,7 @@ int mosquitto_loop_start(struct mosquitto *mosq)
 #elif defined(__FreeBSD__) || defined(__OpenBSD__)
 		pthread_set_name_np(mosq->thread_id, "mosquitto loop");
 #endif
+		mosq->threaded = mosq_ts_self;
 		return MOSQ_ERR_SUCCESS;
 	}else{
 		return MOSQ_ERR_ERRNO;