Merge in 'release/3.1' changes

Author: dotnet-bot

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

@@ -700,7 +700,8 @@ public static StreamResourceInfo GetRemoteStream(Uri uriRemote)
             SiteOfOriginContainer sooContainer = (SiteOfOriginContainer)GetResourcePackage(packageUri);
 
             // the SiteOfOriginContainer is shared across threads;  synchronize access to it
-            lock (_packageLock)
+            // using the same lock object as other uses (PackWebResponse+CachedResponse.GetResponseStream)
+            lock (sooContainer)
             {
                 sooPart = sooContainer.GetPart(partUri) as SiteOfOriginPart;
             }
@@ -2017,8 +2018,9 @@ private static PackagePart GetResourceOrContentPart(Uri uri)
             ResourceContainer resContainer = (ResourceContainer)GetResourcePackage(packageUri);
 
             // the ResourceContainer is shared across threads;  synchronize access to it
+            // using the same lock object as other uses (PackWebResponse+CachedResponse.GetResponseStream)
             PackagePart part = null;
-            lock (_packageLock)
+            lock (resContainer)
             {
                 part = resContainer.GetPart(partUri);
             }
@@ -2417,7 +2419,6 @@ private object RunDispatcher(object ignore)
         static private bool                             _appCreatedInThisAppDomain;
         static private Application                      _appInstance;
         static private Assembly                         _resourceAssembly;
-        static private object                           _packageLock = new Object();
 
         // Keep LoadBamlSyncInfo stack so that the Outer LoadBaml and Inner LoadBaml( ) for the same
         // Uri share the related information.

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Automation/Peers/DataGridColumnHeadersPresenterAutomationPeer.cs

@@ -131,7 +131,7 @@ protected override List<AutomationPeer> GetChildrenCore()
 
                     // protection from indistinguishable items - for example, 2 strings with same value
                     // this scenario does not work in ItemsControl however is not checked for.
-                    if (ItemPeers[dataItem] == null)
+                    if (peer != null && ItemPeers[dataItem] == null)
                     {
                         children.Add(peer);
                         ItemPeers[dataItem] = peer;

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Automation/Peers/GroupItemAutomationPeer.cs

@@ -274,8 +274,8 @@ protected override List<AutomationPeer> GetChildrenCore()
                             // but only if we haven't added a peer for this item during this GetChildrenCore call.
                             bool itemMissingPeerInGlobalStorage = itemsControlAP.ItemPeers[item] == null;
 
-                            if (itemMissingPeerInGlobalStorage
-                                || (peer?.GetParent() == this && addedChildren[item] == null))
+                            if (peer != null && (itemMissingPeerInGlobalStorage
+                                || (peer.GetParent() == this && addedChildren[item] == null)))
                             {
                                 children.Add(peer);
                                 addedChildren[item] = peer;

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Automation/Peers/ItemsControlAutomationPeer.cs

@@ -199,7 +199,7 @@ protected override List<AutomationPeer> GetChildrenCore()
 
                     // protection from indistinguishable items - for example, 2 strings with same value
                     // this scenario does not work in ItemsControl however is not checked for.
-                    if (_dataChildren[dataItem] == null)
+                    if (peer != null && _dataChildren[dataItem] == null)
                     {
                         children.Add(peer);
                         _dataChildren[dataItem] = peer;