From d421b0048288d737b8f499eb788f1f6696eb99e6 Mon Sep 17 00:00:00 2001
From: Erik Darling <2136037+erikdarlingdata@users.noreply.github.com>
Date: Thu, 19 Feb 2026 13:51:41 -0500
Subject: [PATCH] Fix mutex crash on app exit (fixes #89)

ReleaseMutex() throws ApplicationException if called by a thread
that doesn't own the mutex. This happens when the app exits after
detecting a second instance, or when shutdown is triggered from a
non-owning thread. Track ownership and only release if we own it.

Fixed in both Dashboard and Lite.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 Dashboard/App.xaml.cs | 11 +++++++----
 Lite/App.xaml.cs      | 11 +++++++----
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/Dashboard/App.xaml.cs b/Dashboard/App.xaml.cs
index 1a17661f..54af8047 100644
--- a/Dashboard/App.xaml.cs
+++ b/Dashboard/App.xaml.cs
@@ -20,13 +20,14 @@ public partial class App : Application
     {
         private const string MutexName = "PerformanceMonitorDashboard_SingleInstance";
         private Mutex? _singleInstanceMutex;
+        private bool _ownsMutex;
 
         protected override void OnStartup(StartupEventArgs e)
         {
             // Check for existing instance
-            _singleInstanceMutex = new Mutex(true, MutexName, out bool isNewInstance);
+            _singleInstanceMutex = new Mutex(true, MutexName, out _ownsMutex);
 
-            if (!isNewInstance)
+            if (!_ownsMutex)
             {
                 // Another instance is already running - activate it and exit
                 NativeMethods.BroadcastShowMessage();
@@ -58,8 +59,10 @@ protected override void OnExit(ExitEventArgs e)
                 mainWin.ExitApplication();
             }
 
-            // Release the mutex
-            _singleInstanceMutex?.ReleaseMutex();
+            if (_ownsMutex)
+            {
+                _singleInstanceMutex?.ReleaseMutex();
+            }
             _singleInstanceMutex?.Dispose();
 
             base.OnExit(e);
diff --git a/Lite/App.xaml.cs b/Lite/App.xaml.cs
index 47d46db6..950855c7 100644
--- a/Lite/App.xaml.cs
+++ b/Lite/App.xaml.cs
@@ -20,6 +20,7 @@ public partial class App : Application
 {
     private const string MutexName = "PerformanceMonitorLite_SingleInstance";
     private Mutex? _singleInstanceMutex;
+    private bool _ownsMutex;
 
     /// <summary>
     /// Gets the application data directory where config and data files are stored.
@@ -119,9 +120,9 @@ protected override void OnStartup(StartupEventArgs e)
     {
 
         // Check for existing instance
-        _singleInstanceMutex = new Mutex(true, MutexName, out bool isNewInstance);
+        _singleInstanceMutex = new Mutex(true, MutexName, out _ownsMutex);
 
-        if (!isNewInstance)
+        if (!_ownsMutex)
         {
             MessageBox.Show(
                 "Performance Monitor Lite is already running.",
@@ -168,8 +169,10 @@ protected override void OnExit(ExitEventArgs e)
         AppLogger.Info("App", "Shutting down");
         AppLogger.Shutdown();
 
-        // Release the mutex
-        _singleInstanceMutex?.ReleaseMutex();
+        if (_ownsMutex)
+        {
+            _singleInstanceMutex?.ReleaseMutex();
+        }
         _singleInstanceMutex?.Dispose();
 
         base.OnExit(e);