Don't use shared background context for fetching item counts

A significant fraction of the time was spent waiting for the background
context to be available, before the count could even be started. Since
the counts don't need to use the shared background context, let them
each use their own context to avoid contention.

Reader.xcodeproj/xcshareddata/xcschemes/Reader.xcscheme

@@ -77,7 +77,7 @@
          </CommandLineArgument>
          <CommandLineArgument
             argument = "-com.apple.CoreData.SQLDebug 1"
-            isEnabled = "YES">
+            isEnabled = "NO">
          </CommandLineArgument>
       </CommandLineArguments>
       <EnvironmentVariables>

Reader/Screens/AppSplitViewController.swift

@@ -45,7 +45,15 @@ class AppSplitViewController: UISplitViewController {
         setViewController(sidebarNav, for: .primary)
         
         secondaryNav = UINavigationController()
+        #if targetEnvironment(macCatalyst)
         secondaryNav.isNavigationBarHidden = true
+        #else
+        // the toggle sidebar button only appears if there's a navigation bar
+        // so we just make always transparent, rather than disabling it
+        let secondaryNavBarAppearance = UINavigationBarAppearance()
+        secondaryNavBarAppearance.configureWithTransparentBackground()
+        secondaryNav.navigationBar.standardAppearance = secondaryNavBarAppearance
+        #endif
         secondaryNav.view.backgroundColor = .appBackground
         setViewController(secondaryNav, for: .secondary)
         

Reader/Screens/Home/HomeCollectionViewCell.swift

@@ -14,7 +14,7 @@ private let signposter = OSSignposter(subsystem: "net.shadowfacts.Reader", categ
 
 class HomeCollectionViewCell: UICollectionViewListCell {
     
-    private var currentItemListType: ItemListType?
+    private var currentItemCountTask: Task<Void, Never>?
     private var itemCount: Int?
     
     #if !targetEnvironment(macCatalyst)
@@ -31,12 +31,11 @@ class HomeCollectionViewCell: UICollectionViewListCell {
     
     override func prepareForReuse() {
         super.prepareForReuse()
+        currentItemCountTask?.cancel()
         itemCount = nil
     }
     
     func updateUI(item: ItemListType, persistentContainer: PersistentContainer) {
-        self.currentItemListType = item
-        
         var config = UIListContentConfiguration.valueCell()
         config.text = item.title
         if let itemCount {
@@ -45,10 +44,10 @@ class HomeCollectionViewCell: UICollectionViewListCell {
         config.secondaryTextProperties.color = .tintColor
         self.contentConfiguration = config
         
-        Task(priority: .userInitiated) {
-            let state = signposter.beginInterval("fetch count", id: signposter.makeSignpostID())
+        currentItemCountTask = Task(priority: .userInitiated) {
+            let state = signposter.beginInterval("fetch count", id: signposter.makeSignpostID(), "\(String(item.hashValue, radix: 16), privacy: .public)")
             if let count = await fetchCount(item: item, in: persistentContainer),
-               self.currentItemListType == item {
+               !Task.isCancelled {
                 self.itemCount = count
                 config.secondaryText = count.formatted(.number)
                 self.contentConfiguration = config
@@ -62,9 +61,12 @@ class HomeCollectionViewCell: UICollectionViewListCell {
             return nil
         }
         return await withCheckedContinuation({ continuation in
-            let context = persistentContainer.backgroundContext
-            context.perform {
+            let state = signposter.beginInterval("waiting to perform", id: signposter.makeSignpostID(), "\(String(item.hashValue, radix: 16), privacy: .public)")
+            persistentContainer.performBackgroundTask { context in
+                signposter.endInterval("waiting to perform", state)
+                let state = signposter.beginInterval("count", id: signposter.makeSignpostID(), "\(String(item.hashValue, radix: 16), privacy: .public)")
                 let count = try? context.count(for: request)
+                signposter.endInterval("count", state)
                 continuation.resume(returning: count)
             }
         })