Make some lock object as readonly (#4487)

src/Microsoft.DotNet.Wpf/src/Extensions/PresentationFramework-SystemCore/DynamicAccessorImpl.cs

@@ -156,7 +156,7 @@ public static DynamicIndexerAccessor GetIndexerAccessor(int rank)
         MulticastDelegate   _getterDelegate, _setterDelegate;
 
         static DynamicIndexerAccessor[] _accessors = new DynamicIndexerAccessor[1];
-        static object _lock = new object();
+        static readonly object _lock = new object();
     }
 
     #endregion DynamicIndexerAccessor

src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/FontCache/FontCacheUtil.cs

@@ -315,7 +315,7 @@ internal static string CompositeFontExtension
         private const string EmptyFontFamilyReference = "#";
         private const string EmptyCanonicalName = "";
 
-        private static object _dpiLock = new object();
+        private static readonly object _dpiLock = new object();
         private static int    _dpi;
         private static bool   _dpiInitialized = false;
 

src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/FontCache/TypefaceMetricsCache.cs

@@ -68,7 +68,7 @@ internal static void Add(object key, object value)
         }
    
         private static Hashtable _hashTable = new Hashtable(MaxCacheCapacity);
-        private static object _lock         = new object();        
+        private static readonly object _lock         = new object();        
         private const int MaxCacheCapacity  = 64;   // Maximum cache capacity
     }        
 }

src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/IO/Packaging/PreloadedPackages.cs

@@ -241,7 +241,7 @@ internal bool ThreadSafe
         // Hashtable. HybridDictionary already has functionality of switching between
         //  ListDictionary and Hashtable depending on the size of the collection
         static private HybridDictionary _packagePairs;
-        static private Object           _globalLock;
+        static private readonly Object  _globalLock;
 
         #endregion Private Fields
     }

src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/Ink/GestureRecognizer/NativeRecognizer.cs

@@ -834,7 +834,7 @@ enum RECO_TYPE : ushort
         /// <summary>
         /// Used to lock for instancing the native recognizer handle
         /// </summary>
-        private static object                           _syncRoot = new object();
+        private static readonly object                  _syncRoot = new object();
 
         /// <summary>
         /// All NativeRecognizer share a single handle to the recognizer

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/IO/Packaging/PackageStore.cs

@@ -172,7 +172,7 @@ private static void ValidatePackageUri(Uri uri)
         // Hashtable. HybridDictionary already has functionality of switching between
         //  ListDictionary and Hashtable depending on the size of the collection
         static private HybridDictionary _packages;
-        static private Object _globalLock;
+        static private readonly Object _globalLock;
 
         #endregion Private Fields
     }

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/CoreCompatibilityPreferences.cs

@@ -187,6 +187,6 @@ private static void Seal()
         }
 
         private static bool _isSealed;
-        private static object _lockObject = new object();
+        private static readonly object _lockObject = new object();
     }
 }

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/DataFormats.cs

@@ -470,7 +470,7 @@ private static void EnsurePredefined()
         private static ArrayList _formatList;
 
         // This object is for locking the _formatList to access safe in the multi-thread.
-        private static Object _formatListlock = new Object();
+        private static readonly Object _formatListlock = new Object();
 
         #endregion Private Fields
     }

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Diagnostics/XamlSourceInfoHelper.cs

@@ -38,7 +38,7 @@ internal static class XamlSourceInfoHelper
         private static ConditionalWeakTable<object, XamlSourceInfo> s_sourceInfoTable; // no storage by default
 
         // While ConditionalWeakTable is thread safe we need to make multiple calls in a thread safe manner.
-        private static object s_lock = new object();
+        private static readonly object s_lock = new object();
 
         private static PropertyInfo s_sourceBamlUriProperty;
         private static PropertyInfo s_elementLineNumberProperty;

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/EventRouteFactory.cs

@@ -98,7 +98,7 @@ private static EventRoute Pop()
 
         private static EventRoute[] _eventRouteStack;
         private static int _stackTop;
-        private static object _synchronized = new object();
+        private static readonly object _synchronized = new object();
 
         #endregion Data
     }

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/InputManager.cs

@@ -1005,7 +1005,7 @@ private void RequestContinueProcessingStagingArea()
         private static DispatcherOperation _synchronizedInputAsyncClearOperation;
 
         // Lock used to serialize access to synchronized input related static fields.
-        private static object _synchronizedInputLock = new object();
+        private static readonly object _synchronizedInputLock = new object();
 }
 }
 

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Stylus/Common/DynamicRenderer.cs

@@ -1234,7 +1234,7 @@ private void DestroyRealTimeVisuals()
         // For OnRenderComplete support (for UI Thread)
         EventHandler  _onRenderComplete;
         bool          _waitingForRenderComplete;
-        object        __siLock = new object();
+        readonly object        __siLock = new object();
         private StrokeInfo  _renderCompleteStrokeInfo;
 
         // On internal real time ink rendering thread.

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Stylus/Wisp/WispLogic.cs

@@ -3673,11 +3673,11 @@ internal long IncrementVersion()
         bool _inputEnabled = false;
         bool _updatingScreenMeasurements = false;
         DispatcherOperationCallback _processDisplayChanged;
-        object __penContextsLock = new object();
+        readonly object __penContextsLock = new object();
 
         Dictionary<object, PenContexts> __penContextsMap = new Dictionary<object, PenContexts>(2);
 
-        object __stylusDeviceLock = new object();
+        readonly object __stylusDeviceLock = new object();
         Dictionary<int, StylusDevice> __stylusDeviceMap = new Dictionary<int, StylusDevice>(2);
 
         bool _inDragDrop;

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/FactoryMaker.cs

@@ -139,7 +139,7 @@ internal IntPtr ImagingFactoryPtr
         /// "FactoryMaker" is free threaded. This lock is used to synchronize
         /// access to the FactoryMaker.
         /// </summary>
-        private static object s_factoryMakerLock = new object();
+        private static readonly object s_factoryMakerLock = new object();
         private bool _fValidObject;
     }
 }

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Imaging/BitmapDecoder.cs

@@ -1687,7 +1687,7 @@ internal bool CanConvertToString()
         internal UniqueEventHelper<ExceptionEventArgs> _failedEvent = new UniqueEventHelper<ExceptionEventArgs>();
 
         /// SyncObject
-        private object _syncObject = new Object();
+        private readonly object _syncObject = new Object();
 
         // For UnmanagedMemoryStream we want to make sure that buffer
         // its pointing to is not getting release until decoder is alive

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Imaging/BitmapDownload.cs

@@ -472,7 +472,7 @@ Exception e
         private static Thread _thread;
 
         /// lock object
-        private static object _syncLock;
+        private static readonly object _syncLock;
 
         /// Default async read size
         private const int READ_SIZE = 1024;

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/textformatting/TextFormatter.cs

@@ -35,7 +35,7 @@ namespace System.Windows.Media.TextFormatting
     /// </summary>
     public abstract class TextFormatter : IDisposable
     {
-        private static object _staticLock = new object();
+        private static readonly object _staticLock = new object();
 
         /// <summary>
         /// Client to create a new instance of TextFormatter

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/PresentationSource.cs

@@ -792,7 +792,7 @@ private static PresentationSource FindSource(DependencyObject o, bool enable2DTo
         private static readonly RoutedEvent SourceChangedEvent = EventManager.RegisterRoutedEvent("SourceChanged", RoutingStrategy.Direct, typeof(SourceChangedEventHandler), typeof(PresentationSource));
 
         // The lock we use to protect our static data.
-        private static object _globalLock = new object();
+        private static readonly object _globalLock = new object();
 
         // An array of weak-references to sources that we know about.
         private static WeakReferenceList _sources = new WeakReferenceList(_globalLock);

src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/AppModel/AppSecurityManager.cs

@@ -427,7 +427,7 @@ internal class InternetSecurityManager
 
         // Object to be used for locking.  Using typeof(Util) causes an FxCop
         // violation DoNotLockOnObjectsWithWeakIdentity
-        private static object _lockObj = new object();
+        private static readonly object _lockObj = new object();
 
         private static UnsafeNativeMethods.IInternetSecurityManager _secMgr;
 

src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/AppModel/AssemblyFilter.cs

@@ -104,7 +104,7 @@ private void ExtractDisallowedRegistryList()
 
         static SecurityCriticalDataForSet<bool> _disallowedListExtracted;
 
-        static object _lock = new object();
+        static readonly object _lock = new object();
 
         private const string FILEVERSION_STRING = @", FileVersion=";
         // This is the location in the registry where all the keys are stored

src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/AppModel/ResourcePart.cs

@@ -185,7 +185,7 @@ private Stream EnsureResourceLocationSet()
         private SecurityCriticalDataForSet<ResourceManagerWrapper> _rmWrapper;
         private bool _ensureResourceIsCalled = false;
         private string _name;
-        private Object _globalLock = new Object();
+        private readonly Object _globalLock = new Object();
 
         #endregion Private Members
     }

src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/Data/AsyncDataRequest.cs

@@ -219,7 +219,7 @@ bool ChangeStatus(AsyncRequestStatus newStatus)
         AsyncRequestCallback _workCallback;
         AsyncRequestCallback _completedCallback;
 
-        object SyncRoot = new object();     // for synchronization
+        readonly object SyncRoot = new object();     // for synchronization
     }
 
 

src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/Data/DataBindEngine.cs

@@ -755,7 +755,7 @@ internal override void OnShutDown(object target, object sender, EventArgs e)
         private CleanupHelper _cleanupHelper;
 
         private Queue<DataBindOperation> _crossThreadQueue = new Queue<DataBindOperation>();
-        private object _crossThreadQueueLock = new object();
+        private readonly object _crossThreadQueueLock = new object();
         private int _crossThreadCost;
         private DispatcherOperation _crossThreadDispatcherOperation;
         internal const int CrossThreadThreshold = 50000;   // 50 msec

src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/Data/LiveShapingList.cs

@@ -799,7 +799,7 @@ object IEnumerator.Current
 
         static List<DependencyProperty> s_dpList = new List<DependencyProperty>();
         // static list of DPs, shared by all instances of lists
-        static object s_Sync = new object();  // lock for s_dpList
+        static readonly object s_Sync = new object();  // lock for s_dpList
 
         #endregion
     }

src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/Ink/HighContrastHelper.cs

@@ -215,7 +215,7 @@ private static void OnUpdateHighContrast(HighContrastCallback highContrastCallba
 
         #region Private Fields
 
-        private static object                   __lock = new object();
+        private static readonly object          __lock = new object();
         private static List<WeakReference>      __highContrastCallbackList;
         private static int                      __increaseCount;
         private const int                       CleanTolerance = 100;

src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/PtsHost/PtsCache.cs

@@ -765,7 +765,7 @@ private unsafe void InitTableObjInfo(PtsHost ptsHost, ref PTS.FSTABLEOBJINIT tab
         /// <summary>
         /// Lock.
         /// </summary>
-        private object _lock = new object();
+        private readonly object _lock = new object();
 
         /// <summary>
         /// Whether object is already disposed.

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Annotations/Storage/AnnotationStore.cs

@@ -392,7 +392,7 @@ protected bool IsDisposed
         private bool _disposed = false;
 
         /// Private object used for synchronization
-        private Object lockObject = new Object();
+        private readonly Object lockObject = new Object();
 
         #endregion Private Fields
     }

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Diagnostics/ResourceDictionaryDiagnostics.cs

@@ -273,7 +273,7 @@ private static void RemoveResourceDictionaryForUriImpl(Uri uri, ResourceDictiona
         }
 
         private static Dictionary<Uri, List<WeakReference<ResourceDictionary>>> _dictionariesFromUri;
-        private static object _dictionariesFromUriLock = new object();
+        private static readonly object _dictionariesFromUriLock = new object();
         private static IReadOnlyCollection<ResourceDictionary> EmptyResourceDictionaries
             => Array.Empty<ResourceDictionary>();
 

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/Tracing/SpellerCOMActionTraceLogger.cs

@@ -114,7 +114,7 @@ private class InstanceInfo
         /// A lock object to serialize updates to <see cref="_instanceInfos"/>
         /// and the <see cref="InstanceInfo"/> instances contained therein.
         /// </summary>
-        private static object _lockObject = new object();
+        private static readonly object _lockObject = new object();
 
         /// <summary>
         /// The current COM action being tracked
@@ -298,4 +298,4 @@ private struct SpellerCOMTimingData
             public long RunningAverageCallTimeForCOMCallsMs { get; set; }
         }
     }
-}
\ No newline at end of file
+}

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/FrameworkCompatibilityPreferences.cs

@@ -478,6 +478,6 @@ private static void Seal()
         }
 
         private static bool _isSealed;
-        private static object _lockObject = new object();
+        private static readonly object _lockObject = new object();
     }
 }

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/FrameworkElementFactory.cs

@@ -1320,7 +1320,7 @@ private bool IsValueDefined(DependencyProperty dp)
         private FrameworkElementFactory _nextSibling;
 
         // Instance-based synchronization
-        private object _synchronized = new object();
+        private readonly object _synchronized = new object();
     }
 }
 

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/Baml2006/Baml2006SchemaContext.cs

@@ -708,7 +708,7 @@ private bool TryGetBamlProperty(Int16 propertyId, out BamlProperty bamlProperty,
         private static readonly Lazy<XamlType> _staticResourceExtensionType
             = new Lazy<XamlType>(() => System.Windows.Markup.XamlReader.BamlSharedSchemaContext.GetXamlType(typeof(StaticResourceExtension)));
 
-        private object _syncObject = new object();
+        private readonly object _syncObject = new object();
 
         private Assembly _localAssembly;
 

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/Baml2006/WpfSharedXamlSchemaContext.cs

@@ -64,7 +64,7 @@ internal XamlType GetXamlTypeInternal(string xamlNamespace, string name, params
         }
 
         private Dictionary<Type, XamlType> _masterTypeTable = new Dictionary<Type, XamlType>();
-        private object _syncObject = new Object();
+        private readonly object _syncObject = new Object();
         private bool _useV3Rules;
     }
 }

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/Primitives/ElementMarkupObject.cs

@@ -406,7 +406,7 @@ private bool TryGetConstructorInfoArguments(object instance, out ParameterInfo[]
             return false;
         }
 
-        private static object _shouldSerializeCacheLock = new object();
+        private static readonly object _shouldSerializeCacheLock = new object();
         private static Hashtable _shouldSerializeCache = new Hashtable();
         private static Type[] _shouldSerializeArgsObject = new Type[] { typeof(DependencyObject) };
         private static Type[] _shouldSerializeArgsManager = new Type[] { typeof(XamlDesignerSerializationManager) };

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/Primitives/MarkupWriter.cs

@@ -1561,7 +1561,7 @@ private static class NamespaceCache
         {
             private static Dictionary<Assembly, Dictionary<string, string>> XmlnsDefinitions = new Dictionary<Assembly, Dictionary<string, string>>();
             private static Dictionary<string, string> DefaultPrefixes = new Dictionary<string, string>();
-            private static object SyncObject = new object();
+            private static readonly object SyncObject = new object();
 
             static Dictionary<string, string> GetMappingsFor(Assembly assembly)
             {

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/XamlTypeMapperSchemaContext.cs

@@ -24,7 +24,7 @@ internal class XamlTypeMapperSchemaContext : XamlSchemaContext
             WpfSharedXamlSchemaContext _sharedSchemaContext;
 
             // Lock on syncObject
-            object syncObject = new object();
+            readonly object syncObject = new object();
             Dictionary<string, string> _piNamespaces;
             IEnumerable<string> _allXamlNamespaces;
             Dictionary<Type, XamlType> _allowedInternalTypes;

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/TriggerBase.cs

@@ -393,7 +393,7 @@ internal TriggerCondition[] TriggerConditions
         /* property */ internal FrugalStructList<System.Windows.PropertyValue> PropertyValues = new FrugalStructList<System.Windows.PropertyValue>();
 
         // Global, cross-object synchronization
-        private static object Synchronized = new object();
+        private static readonly object Synchronized = new object();
 
         // Conditions
         TriggerCondition[] _triggerConditions;

src/Microsoft.DotNet.Wpf/src/Shared/Telemetry/Managed/TraceLoggingProvider.cs

@@ -51,7 +51,7 @@ internal static EventSource GetProvider()
         }
 
         private static EventSource _logger;
-        private static object _lockObject = new object();
+        private static readonly object _lockObject = new object();
 
 #if WINDOWS_BASE
         /// <summary>
@@ -70,4 +70,4 @@ internal static EventSource GetProvider()
         private static readonly string ProviderName = "Microsoft.DOTNET.WPF.PresentationFramework";
 #endif
     }
-}
\ No newline at end of file
+}

src/Microsoft.DotNet.Wpf/src/System.Windows.Controls.Ribbon/Microsoft/Windows/Controls/Ribbon/NativeMethods.cs

@@ -441,7 +441,7 @@ internal static class HandleCollector
         private static HandleType[] handleTypes;
         private static int handleTypeCount = 0;
 
-        private static Object handleMutex = new Object();
+        private static readonly Object handleMutex = new Object();
 
         /// <devdoc>
         ///     Adds the given handle to the handle collector.  This keeps the

src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/ValueSerializer.cs

@@ -284,7 +284,7 @@ protected Exception GetConvertFromException(object value)
             TypeDescriptor.Refreshed += TypeDescriptorRefreshed;
         }
 
-        private static object _valueSerializersLock = new object();
+        private static readonly object _valueSerializersLock = new object();
         private static Hashtable _valueSerializers = new Hashtable();
     }
 }

src/Microsoft.DotNet.Wpf/src/Themes/PresentationFramework.Classic/Microsoft/Windows/Themes/ClassicBorderDecorator.cs

@@ -505,7 +505,7 @@ private static bool IsValidBorderStyle(object o)
         /// If BorderBrush is not set to ClassicBorderBrush, a flat style is drawn
         /// </summary>
         private static Brush _classicBorderBrush;
-        private static object _brushLock = new object();
+        private static readonly object _brushLock = new object();
 
         public static Brush ClassicBorderBrush
         {

src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClient/MS/Internal/Automation/ClientEventManager.cs

@@ -731,7 +731,7 @@ private enum Tracker
         private static QueueProcessor _callbackQueue;      // callbacks are queued on this class to avoid deadlocks
         private static bool _isBkgrdThreadRunning = false; // is there a background thread for queueing and recieving WinEvents?
         private static ArrayList _listeners;               // data representing events the client is listening for
-        private static object _classLock = new object();   // use lock object vs typeof(class) for perf reasons
+        private static readonly object _classLock = new object();   // use lock object vs typeof(class) for perf reasons
 
         #endregion Private Fields
     }

src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClient/MS/Internal/Automation/ProxyManager.cs

@@ -828,7 +828,7 @@ private enum ProxyScoping
             FallbackHandlers,
         }
         
-        private static object _lockObj = new object();
+        private static readonly object _lockObj = new object();
 
         // contains ClientSideProviderDescription structs or an Arraylist of ClientSideProviderDescription structs
         private static Hashtable _classHandlers = new Hashtable(22, 1.0f);

src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClient/System/Windows/Automation/CacheRequest.cs

@@ -512,7 +512,7 @@ void Invalidate()
         int _refCount = 0;
 
         // Used to lock on this instance...
-        object _instanceLock = null;
+        readonly object _instanceLock = null;
 
         //--- Per-Thread state ---
 

src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClientSideProviders/MS/Internal/AutomationProxies/EventManager.cs

@@ -582,7 +582,7 @@ private static void InitObjectIdMenu()
         private static Hashtable _objectIdScroll;
         private static Hashtable _objectIdCaret;
         private static Hashtable _objectIdMenu;
-        private static object _classLock = new object();   // use lock object vs typeof(class) for perf 
+        private static readonly object _classLock = new object();   // use lock object vs typeof(class) for perf 
 
         // The hwndLast and objLast is to allow limited filtering of events.
         private static IntPtr _hwndLast = IntPtr.Zero;

src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClientSideProviders/MS/Internal/AutomationProxies/WinEventTracker.cs

@@ -589,7 +589,7 @@ private enum EventFlag
         // WinEventHooks must be processed in the same thread that created them.
         // Use a seperate thread to manage the hooks
         private static QueueProcessor _callbackQueue = null;
-        private static object _queueLock = new object();
+        private static readonly object _queueLock = new object();
 
         // static: Array of Hashtables, one per WinEvent Id. 
         // Each Hashtable contains EventHookParams classes the key is the process id.

src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/BaseCompatibilityPreferences.cs

@@ -385,6 +385,6 @@ private static void Seal()
         }
 
         private static bool _isSealed;
-        private static object _lockObject = new object();
+        private static readonly object _lockObject = new object();
     }
 }

src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/DependencyObjectType.cs

@@ -231,7 +231,7 @@ private DependencyObjectType()
         // Synchronized: Covered by DispatcherLock
         private static int DTypeCount = 0;
 
-        private static object _lock = new object();
+        private static readonly object _lock = new object();
     }
 }
 

src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/Threading/Dispatcher.cs

@@ -2879,7 +2879,7 @@ private object[] CombineParameters(object arg, object[] args)
 
         private static List<WeakReference> _dispatchers;
         private static WeakReference _possibleDispatcher;
-        private static object _globalLock;
+        private static readonly object _globalLock;
 
         [ThreadStatic]
         private static Dispatcher _tlsDispatcher;      // use TLS for ownership only

src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/Threading/DispatcherHooks.cs

@@ -243,7 +243,7 @@ internal void RaiseOperationAborted(Dispatcher dispatcher, DispatcherOperation o
             }
         }
 
-        private object _instanceLock = new object();
+        private readonly object _instanceLock = new object();
 
         private EventHandler _dispatcherInactive;
 

src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/Threading/DispatcherTimer.cs

@@ -319,7 +319,7 @@ private object FireTick()
         }
         
         // This is the object we use to synchronize access.
-        private object _instanceLock = new object();
+        private readonly object _instanceLock = new object();
         
         // Note: We cannot BE a dispatcher-affinity object because we can be
         // created by a worker thread.  We are still associated with a

src/Microsoft.DotNet.Wpf/src/WindowsFormsIntegration/System/Windows/Integration/ApplicationInterop.cs

@@ -308,7 +308,7 @@ public bool PreFilterMessage(ref SWF.Message msg)
     internal class WeakReferenceList<T> where T : class
     {
         List<WeakReference> _internalList;
-        object _syncRoot = new object();
+        readonly object _syncRoot = new object();
 
         public WeakReferenceList()
             : base()