From f87390e2185fde6b3b6fd6a49e6632bae3d0a448 Mon Sep 17 00:00:00 2001
From: Shadowghost <Shadowghost@users.noreply.github.com>
Date: Tue, 15 Sep 2026 11:17:03 -0400
Subject: Backport pull request #18020 from jellyfin/release-12.z

Stop the library monitor from refreshing against a disposed host

Original-merge: 3aec32cb249ba54a9b6c0c799d2ff84848069722

Merged-by: crobibero <cody@robibe.ro>

Backported-by: Cody Robibero <cody@robibe.ro>
---
 Emby.Server.Implementations/IO/LibraryMonitor.cs | 32 +++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)

(limited to 'Emby.Server.Implementations/IO/LibraryMonitor.cs')

diff --git a/Emby.Server.Implementations/IO/LibraryMonitor.cs b/Emby.Server.Implementations/IO/LibraryMonitor.cs
index 0f92e2f03e..e51c863f86 100644
--- a/Emby.Server.Implementations/IO/LibraryMonitor.cs
+++ b/Emby.Server.Implementations/IO/LibraryMonitor.cs
@@ -3,6 +3,7 @@ using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 using Emby.Server.Implementations.Library;
 using MediaBrowser.Controller.Configuration;
@@ -40,6 +41,12 @@ namespace Emby.Server.Implementations.IO
         /// </summary>
         private readonly ConcurrentDictionary<string, string> _tempIgnoredPaths = new(StringComparer.OrdinalIgnoreCase);
 
+        /// <summary>
+        /// Incremented by every <see cref="Stop"/> so watchers still being created on a background
+        /// task can tell that the sweep they should have been caught by has already run.
+        /// </summary>
+        private int _watcherGeneration;
+
         private bool _disposed;
 
         /// <summary>
@@ -69,7 +76,7 @@ namespace Emby.Server.Implementations.IO
             _dotIgnoreIgnoreRule = dotIgnoreIgnoreRule;
 
             appLifetime.ApplicationStarted.Register(Start);
-            appLifetime.ApplicationStopping.Register(Stop);
+            appLifetime.ApplicationStopping.Register(Dispose);
         }
 
         /// <inheritdoc />
@@ -120,6 +127,11 @@ namespace Emby.Server.Implementations.IO
         /// <inheritdoc />
         public void Start()
         {
+            if (_disposed)
+            {
+                return;
+            }
+
             _libraryManager.ItemAdded += OnLibraryManagerItemAdded;
             _libraryManager.ItemRemoved += OnLibraryManagerItemRemoved;
 
@@ -233,6 +245,8 @@ namespace Emby.Server.Implementations.IO
                 return;
             }
 
+            var generation = Volatile.Read(ref _watcherGeneration);
+
             // Creating a FileSystemWatcher over the LAN can take hundreds of milliseconds, so wrap it in a Task to do them all in parallel
             Task.Run(() =>
             {
@@ -256,7 +270,11 @@ namespace Emby.Server.Implementations.IO
                     newWatcher.Changed += OnWatcherChanged;
                     newWatcher.Error += OnWatcherError;
 
-                    if (_fileSystemWatchers.TryAdd(path, newWatcher))
+                    if (_disposed || Volatile.Read(ref _watcherGeneration) != generation)
+                    {
+                        DisposeWatcher(newWatcher, false);
+                    }
+                    else if (_fileSystemWatchers.TryAdd(path, newWatcher))
                     {
                         newWatcher.EnableRaisingEvents = true;
                         _logger.LogInformation("Watching directory {Path}", path);
@@ -357,6 +375,11 @@ namespace Emby.Server.Implementations.IO
         {
             ArgumentException.ThrowIfNullOrEmpty(path);
 
+            if (_disposed)
+            {
+                return;
+            }
+
             if (IgnorePatterns.ShouldIgnore(path))
             {
                 return;
@@ -452,6 +475,8 @@ namespace Emby.Server.Implementations.IO
         /// </summary>
         public void Stop()
         {
+            Interlocked.Increment(ref _watcherGeneration);
+
             _libraryManager.ItemAdded -= OnLibraryManagerItemAdded;
             _libraryManager.ItemRemoved -= OnLibraryManagerItemRemoved;
 
@@ -496,8 +521,9 @@ namespace Emby.Server.Implementations.IO
                 return;
             }
 
-            Stop();
+            // Set before stopping so anything racing us stops handing out new work.
             _disposed = true;
+            Stop();
         }
     }
 }
-- 
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