From 5e7f670c91a7b24dc01dedece337acbb18c746d2 Mon Sep 17 00:00:00 2001
From: "jan.nijtmans" <nijtmans@users.sourceforge.net>
Date: Wed, 24 Sep 2025 08:52:58 +0000
Subject: Add a panic to MutexDestroy if the mutex is still owned

---
 unix/tclUnixThrd.c | 11 ++++++++++-
 win/tclWinThrd.c   |  3 +++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/unix/tclUnixThrd.c b/unix/tclUnixThrd.c
index da88cdb..ae6d96a 100644
--- a/unix/tclUnixThrd.c
+++ b/unix/tclUnixThrd.c
@@ -95,8 +95,17 @@ static void
 PMutexDestroy(
     PMutex *pmutexPtr)
 {
-#if defined(HAVE_PTHREAD_SPIN_LOCK) && !defined(HAVE_STDATOMIC_H)
+#ifdef HAVE_STDATOMIC_H
+    if (__atomic_load_n(&pmutexPtr->thread, __ATOMIC_SEQ_CST) != 0) {
+	Tcl_Panic("mutex still owned");
+    }
+#else
+    if (mutexPtr->thread != 0) {
+	Tcl_Panic("mutex still owned");
+    }
+# if defined(HAVE_PTHREAD_SPIN_LOCK)
     pthread_spin_destroy(&pmutexPtr->lock);
+# endif
 #endif
     pthread_mutex_destroy(&pmutexPtr->mutex);
 }
diff --git a/win/tclWinThrd.c b/win/tclWinThrd.c
index ab4a3c9..4afa334 100644
--- a/win/tclWinThrd.c
+++ b/win/tclWinThrd.c
@@ -554,6 +554,9 @@ static void
 WMutexDestroy(
     WMutex *wmutexPtr)
 {
+    if (InterlockedOr(&wmPtr->thread, 0) != 0) {
+	Tcl_Panic("mutex still owned");
+    }
     DeleteCriticalSection(&wmutexPtr->crit);
 }
 
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