Prefetch on a background queue to avoid blocking main queue with

CoreData lookups

Tusker.xcodeproj/project.pbxproj

@@ -227,6 +227,7 @@
 		D6A5BB2D23BBA9C4003BF21D /* MyProfileTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6A5BB2C23BBA9C4003BF21D /* MyProfileTests.swift */; };
 		D6A5BB2F23BBAC97003BF21D /* DelegatingResponse.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6A5BB2E23BBAC97003BF21D /* DelegatingResponse.swift */; };
 		D6A5BB3123BBAD87003BF21D /* JSONResponse.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6A5BB3023BBAD87003BF21D /* JSONResponse.swift */; };
+		D6A6C10525B6138A00298D0F /* StatusTablePrefetching.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6A6C10425B6138A00298D0F /* StatusTablePrefetching.swift */; };
 		D6AC956723C4347E008C9946 /* MainSceneDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6AC956623C4347E008C9946 /* MainSceneDelegate.swift */; };
 		D6ACE1AC240C3BAD004EA8E2 /* Ambassador.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = D65F613023AE99E000F3CFD3 /* Ambassador.framework */; };
 		D6ACE1AD240C3BAD004EA8E2 /* Embassy.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = D65F612D23AE990C00F3CFD3 /* Embassy.framework */; };
@@ -587,6 +588,7 @@
 		D6A5BB2C23BBA9C4003BF21D /* MyProfileTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MyProfileTests.swift; sourceTree = "<group>"; };
 		D6A5BB2E23BBAC97003BF21D /* DelegatingResponse.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = DelegatingResponse.swift; sourceTree = "<group>"; };
 		D6A5BB3023BBAD87003BF21D /* JSONResponse.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = JSONResponse.swift; sourceTree = "<group>"; };
+		D6A6C10425B6138A00298D0F /* StatusTablePrefetching.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StatusTablePrefetching.swift; sourceTree = "<group>"; };
 		D6AC956623C4347E008C9946 /* MainSceneDelegate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MainSceneDelegate.swift; sourceTree = "<group>"; };
 		D6AEBB3D2321638100E5038B /* UIActivity+Types.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "UIActivity+Types.swift"; sourceTree = "<group>"; };
 		D6AEBB402321642700E5038B /* SendMesasgeActivity.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SendMesasgeActivity.swift; sourceTree = "<group>"; };
@@ -1389,6 +1391,7 @@
 				D6B81F3B2560365300F6E31D /* RefreshableViewController.swift */,
 				D65234C8256189D0001AF9CF /* TimelineLikeTableViewController.swift */,
 				D625E4812588262A0074BB2B /* DraggableTableViewCell.swift */,
+				D6A6C10425B6138A00298D0F /* StatusTablePrefetching.swift */,
 			);
 			path = Utilities;
 			sourceTree = "<group>";
@@ -2060,6 +2063,7 @@
 				D6E426B325337C7000C02E1C /* CustomEmojiImageView.swift in Sources */,
 				D6D4DDD0212518A000E1C4BB /* AppDelegate.swift in Sources */,
 				D6412B0924B0291E00F5412E /* MyProfileViewController.swift in Sources */,
+				D6A6C10525B6138A00298D0F /* StatusTablePrefetching.swift in Sources */,
 				D6B053A423BD2C8100A066FA /* AssetCollectionsListViewController.swift in Sources */,
 				D690797324A4EF9700023A34 /* UIBezierPath+Helpers.swift in Sources */,
 				D693DE5723FE1A6A0061E07D /* EnhancedNavigationViewController.swift in Sources */,

Tusker/CoreData/MastodonCachePersistentStore.swift

@@ -24,6 +24,12 @@ class MastodonCachePersistentStore: NSPersistentContainer {
         return context
     }()
     
+    private(set) lazy var prefetchBackgroundContext: NSManagedObjectContext = {
+        let context = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
+        context.parent = self.viewContext
+        return context
+    }()
+    
     let statusSubject = PassthroughSubject<String, Never>()
     let accountSubject = PassthroughSubject<String, Never>()
     let relationshipSubject = PassthroughSubject<String, Never>()

Tusker/Screens/Bookmarks/BookmarksTableViewController.swift

@@ -162,24 +162,19 @@ extension BookmarksTableViewController: StatusTableViewCellDelegate {
     }
 }
 
-extension BookmarksTableViewController: UITableViewDataSourcePrefetching {
+extension BookmarksTableViewController: UITableViewDataSourcePrefetching, StatusTablePrefetching {
     func tableView(_ tableView: UITableView, prefetchRowsAt indexPaths: [IndexPath]) {
-        for indexPath in indexPaths {
+        let ids = indexPaths.map { statuses[$0.row].id }
-            guard let status = mastodonController.persistentContainer.status(for: statuses[indexPath.row].id) else { continue }
+        prefetchStatuses(with: ids)
-            _ = ImageCache.avatars.get(status.account.avatar, completion: nil)
-            for attachment in status.attachments where attachment.kind == .image {
-                _ = ImageCache.attachments.get(attachment.url, completion: nil)
-            }
-        }
     }
     
     func tableView(_ tableView: UITableView, cancelPrefetchingForRowsAt indexPaths: [IndexPath]) {
-        for indexPath in indexPaths {
+        let ids: [String] = indexPaths.compactMap {
-            guard let status = mastodonController.persistentContainer.status(for: statuses[indexPath.row].id) else { continue }
+            guard $0.row < statuses.count else {
-            ImageCache.avatars.cancelWithoutCallback(status.account.avatar)
+                return nil
-            for attachment in status.attachments where attachment.kind == .image {
+            }
-                ImageCache.attachments.cancelWithoutCallback(attachment.url)
+            return statuses[$0.row].id
-            }
+        }
-        }
+        cancelPrefetchingStatuses(with: ids)
     }
 }

Tusker/Screens/Conversation/ConversationTableViewController.swift

@@ -7,7 +7,6 @@
 //
 
 import UIKit
-import SafariServices
 import Pachyderm
 
 class ConversationTableViewController: EnhancedTableViewController {
@@ -188,24 +187,14 @@ extension ConversationTableViewController: StatusTableViewCellDelegate {
     }
 }
 
-extension ConversationTableViewController: UITableViewDataSourcePrefetching {
+extension ConversationTableViewController: UITableViewDataSourcePrefetching, StatusTablePrefetching {
     func tableView(_ tableView: UITableView, prefetchRowsAt indexPaths: [IndexPath]) {
-        for indexPath in indexPaths {
+        let ids = indexPaths.map { statuses[$0.row].id }
-            guard let status = mastodonController.persistentContainer.status(for: statuses[indexPath.row].id) else { continue }
+        prefetchStatuses(with: ids)
-            _ = ImageCache.avatars.get(status.account.avatar, completion: nil)
-            for attachment in status.attachments where attachment.kind == .image {
-                _ = ImageCache.attachments.get(attachment.url, completion: nil)
-            }
-        }
     }
     
     func tableView(_ tableView: UITableView, cancelPrefetchingForRowsAt indexPaths: [IndexPath]) {
-        for indexPath in indexPaths {
+        let ids: [String] = indexPaths.compactMap { statuses[$0.row].id }
-            guard let status = mastodonController.persistentContainer.status(for: statuses[indexPath.row].id) else { continue }
+        cancelPrefetchingStatuses(with: ids)
-            ImageCache.avatars.cancelWithoutCallback(status.account.avatar)
-            for attachment in status.attachments where attachment.kind == .image {
-                ImageCache.attachments.cancelWithoutCallback(attachment.url)
-            }
-        }
     }
 }

Tusker/Screens/Profile/ProfileStatusesViewController.swift

@@ -241,33 +241,20 @@ extension ProfileStatusesViewController: StatusTableViewCellDelegate {
     }
 }
 
-extension ProfileStatusesViewController: UITableViewDataSourcePrefetching {
+extension ProfileStatusesViewController: UITableViewDataSourcePrefetching, StatusTablePrefetching {
     func tableView(_ tableView: UITableView, prefetchRowsAt indexPaths: [IndexPath]) {
-        for indexPath in indexPaths {
+        let ids = indexPaths.map { item(for: $0).id }
-            let statusID = item(for: indexPath).id
+        prefetchStatuses(with: ids)
-            
-            guard let status = mastodonController.persistentContainer.status(for: statusID) else {
-                continue
-            }
-            
-            _ = ImageCache.avatars.get(status.account.avatar, completion: nil)
-            for attachment in status.attachments where attachment.kind == .image {
-                _ = ImageCache.attachments.get(attachment.url, completion: nil)
-            }
-        }
     }
     
     func tableView(_ tableView: UITableView, cancelPrefetchingForRowsAt indexPaths: [IndexPath]) {
-        for indexPath in indexPaths {
+        let ids: [String] = indexPaths.compactMap {
-            let statusID = item(for: indexPath).id
+            guard $0.section < sections.count,
-            
+                  $0.row < sections[$0.section].count else {
-            guard let status = mastodonController.persistentContainer.status(for: statusID) else {
+                return nil
-                continue
-            }
-            ImageCache.avatars.cancelWithoutCallback(status.account.avatar)
-            for attachment in status.attachments where attachment.kind == .image {
-                ImageCache.avatars.cancelWithoutCallback(attachment.url)
-            }
             }
+            return item(for: $0).id
+        }
+        cancelPrefetchingStatuses(with: ids)
     }
 }

Tusker/Screens/Timeline/TimelineTableViewController.swift

@@ -150,32 +150,20 @@ extension TimelineTableViewController: StatusTableViewCellDelegate {
     }
 }
 
-extension TimelineTableViewController: UITableViewDataSourcePrefetching {
+extension TimelineTableViewController: UITableViewDataSourcePrefetching, StatusTablePrefetching {
     func tableView(_ tableView: UITableView, prefetchRowsAt indexPaths: [IndexPath]) {
-        for indexPath in indexPaths {
+        let ids = indexPaths.map { item(for: $0).id }
-            guard let status = mastodonController.persistentContainer.status(for: item(for: indexPath).id) else {
+        prefetchStatuses(with: ids)
-                continue
-            }
-            _ = ImageCache.avatars.get(status.account.avatar, completion: nil)
-            for attachment in status.attachments where attachment.kind == .image {
-                _ = ImageCache.attachments.get(attachment.url, completion: nil)
-            }
-        }
     }
     
     func tableView(_ tableView: UITableView, cancelPrefetchingForRowsAt indexPaths: [IndexPath]) {
-        for indexPath in indexPaths {
+        let ids: [String] = indexPaths.compactMap {
-            // todo: this means when removing cells, we can't cancel prefetching
+            guard $0.section < sections.count,
-            // is this an issue?
+                  $0.row < sections[$0.section].count else {
-            guard indexPath.section < sections.count,
+                return nil
-                  indexPath.row < sections[indexPath.section].count,
-                  let status = mastodonController.persistentContainer.status(for: item(for: indexPath).id) else {
-                continue
-            }
-            ImageCache.avatars.cancelWithoutCallback(status.account.avatar)
-            for attachment in status.attachments where attachment.kind == .image {
-                ImageCache.attachments.cancelWithoutCallback(attachment.url)
-            }
             }
+            return item(for: $0).id
+        }
+        cancelPrefetchingStatuses(with: ids)
     }
 }

Tusker/Screens/Utilities/StatusTablePrefetching.swift

@@ -0,0 +1,53 @@
+//
+//  StatusTablePrefetching.swift
+//  Tusker
+//
+//  Created by Shadowfacts on 1/18/21.
+//  Copyright © 2021 Shadowfacts. All rights reserved.
+//
+
+import Foundation
+import CoreData
+
+protocol StatusTablePrefetching: TuskerNavigationDelegate {
+}
+
+extension StatusTablePrefetching {
+    
+    func prefetchStatuses(with ids: [String]) {
+        let context = apiController.persistentContainer.prefetchBackgroundContext
+        context.perform {
+            guard let statuses = getStatusesWith(ids: ids, in: context) else {
+                return
+            }
+            for status in statuses {
+                _ = ImageCache.avatars.get(status.account.avatar, completion: nil)
+                for attachment in status.attachments where attachment.kind == .image {
+                    _ = ImageCache.attachments.get(attachment.url, completion: nil)
+                }
+            }
+        }
+    }
+    
+    func cancelPrefetchingStatuses(with ids: [String]) {
+        let context = apiController.persistentContainer.prefetchBackgroundContext
+        context.perform {
+            guard let statuses = getStatusesWith(ids: ids, in: context) else {
+                return
+            }
+            for status in statuses {
+                ImageCache.avatars.cancelWithoutCallback(status.account.avatar)
+                for attachment in status.attachments where attachment.kind == .image {
+                    ImageCache.attachments.cancelWithoutCallback(attachment.url)
+                }
+            }
+        }
+    }
+    
+}
+
+fileprivate func getStatusesWith(ids: [String], in context: NSManagedObjectContext) -> [StatusMO]? {
+    let request: NSFetchRequest<StatusMO> = StatusMO.fetchRequest()
+    request.predicate = NSPredicate(format: "id IN %@", ids)
+    return try? context.fetch(request)
+}