Use MultiThreadedDictionary for ImageCache request groups

Prevents a crash due a race condition if multiple requets complete
simultaneously and attempt to modify the dictionary

Tusker.xcodeproj/project.pbxproj

@@ -140,7 +140,7 @@
 		D64BC19223C271D9000D0238 /* MastodonActivity.swift in Sources */ = {isa = PBXBuildFile; fileRef = D64BC19123C271D9000D0238 /* MastodonActivity.swift */; };
 		D64D0AAD2128D88B005A6F37 /* LocalData.swift in Sources */ = {isa = PBXBuildFile; fileRef = D64D0AAC2128D88B005A6F37 /* LocalData.swift */; };
 		D64D0AB12128D9AE005A6F37 /* OnboardingViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D64D0AB02128D9AE005A6F37 /* OnboardingViewController.swift */; };
-		D64D8CA92463B494006B0BAA /* CachedDictionary.swift in Sources */ = {isa = PBXBuildFile; fileRef = D64D8CA82463B494006B0BAA /* CachedDictionary.swift */; };
+		D64D8CA92463B494006B0BAA /* MultiThreadDictionary.swift in Sources */ = {isa = PBXBuildFile; fileRef = D64D8CA82463B494006B0BAA /* MultiThreadDictionary.swift */; };
 		D64F80E2215875CC00BEF393 /* XCBActionType.swift in Sources */ = {isa = PBXBuildFile; fileRef = D64F80E1215875CC00BEF393 /* XCBActionType.swift */; };
 		D6531DEE246B81C9000F9538 /* GifvAttachmentView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6531DED246B81C9000F9538 /* GifvAttachmentView.swift */; };
 		D6531DF0246B867E000F9538 /* GifvAttachmentViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6531DEF246B867E000F9538 /* GifvAttachmentViewController.swift */; };
@@ -471,7 +471,7 @@
 		D64BC19123C271D9000D0238 /* MastodonActivity.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MastodonActivity.swift; sourceTree = "<group>"; };
 		D64D0AAC2128D88B005A6F37 /* LocalData.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LocalData.swift; sourceTree = "<group>"; };
 		D64D0AB02128D9AE005A6F37 /* OnboardingViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = OnboardingViewController.swift; sourceTree = "<group>"; };
-		D64D8CA82463B494006B0BAA /* CachedDictionary.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CachedDictionary.swift; sourceTree = "<group>"; };
+		D64D8CA82463B494006B0BAA /* MultiThreadDictionary.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MultiThreadDictionary.swift; sourceTree = "<group>"; };
 		D64F80E1215875CC00BEF393 /* XCBActionType.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = XCBActionType.swift; sourceTree = "<group>"; };
 		D6531DED246B81C9000F9538 /* GifvAttachmentView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GifvAttachmentView.swift; sourceTree = "<group>"; };
 		D6531DEF246B867E000F9538 /* GifvAttachmentViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GifvAttachmentViewController.swift; sourceTree = "<group>"; };
@@ -1360,7 +1360,7 @@
 				D6945C2E23AC47C3005C403C /* SavedDataManager.swift */,
 				D6C693EE216192C2007D6A6D /* TuskerNavigationDelegate.swift */,
 				D6DFC69F242C4CCC00ACC392 /* WeakArray.swift */,
-				D64D8CA82463B494006B0BAA /* CachedDictionary.swift */,
+				D64D8CA82463B494006B0BAA /* MultiThreadDictionary.swift */,
 				D60E2F2B24423EAD005F8713 /* LazilyDecoding.swift */,
 				D6CA6A91249FAD8900AD45C1 /* AudioSessionHelper.swift */,
 				D6E4269C2532A3E100C02E1C /* FuzzyMatcher.swift */,
@@ -1928,7 +1928,7 @@
 				D641C773213CAA25004B4513 /* NotificationsTableViewController.swift in Sources */,
 				D6412B0524B0227D00F5412E /* ProfileViewController.swift in Sources */,
 				D64BC18A23C16487000D0238 /* UnpinStatusActivity.swift in Sources */,
-				D64D8CA92463B494006B0BAA /* CachedDictionary.swift in Sources */,
+				D64D8CA92463B494006B0BAA /* MultiThreadDictionary.swift in Sources */,
 				D6757A7C2157E01900721E32 /* XCBManager.swift in Sources */,
 				D6F1F84D2193B56E00F5FE67 /* Cache.swift in Sources */,
 				D6F0B12B24A3071C001E48C3 /* MainSplitViewController.swift in Sources */,

Tusker/CachedDictionary.swift

@@ -1,35 +0,0 @@
-//
-//  CachedDictionary.swift
-//  Tusker
-//
-//  Created by Shadowfacts on 5/6/20.
-//  Copyright © 2020 Shadowfacts. All rights reserved.
-//
-
-import Foundation
-
-class CachedDictionary<Value> {
-    private let name: String
-    private var dict = [String: Value]()
-    private let queue: DispatchQueue
-    
-    init(name: String) {
-        self.name = name
-        self.queue = DispatchQueue(label: "CachedDictionary (\(name)) Coordinator", attributes: .concurrent)
-    }
-    
-    subscript(key: String) -> Value? {
-        get {
-            var result: Value? = nil
-            queue.sync {
-                result = dict[key]
-            }
-            return result
-        }
-        set(value) {
-            queue.async(flags: .barrier) {
-                self.dict[key] = value
-            }
-        }
-    }
-}

Tusker/Caching/ImageCache.swift

@@ -24,7 +24,7 @@ class ImageCache {
 
     private let cache: Cache<Data>
     
-    private var groups = [URL: RequestGroup]()
+    private var groups = MultiThreadDictionary<URL, RequestGroup>(name: "ImageCache request groups")
     
     init(name: String, memoryExpiry expiry: Expiry) {
         let storage = MemoryStorage<Data>(config: MemoryConfig(expiry: expiry))
@@ -56,7 +56,7 @@ class ImageCache {
                     if let data = data {
                         try? self.cache.setObject(data, forKey: key)
                     }
-                    self.groups.removeValue(forKey: url)
+                    self.groups.removeValueWithoutReturning(forKey: url)
                 }
                 groups[url] = group
                 let request = group.addCallback(completion)

Tusker/MultiThreadDictionary.swift

@@ -0,0 +1,50 @@
+//
+//  MultiThreadDictionary.swift
+//  Tusker
+//
+//  Created by Shadowfacts on 5/6/20.
+//  Copyright © 2020 Shadowfacts. All rights reserved.
+//
+
+import Foundation
+
+class MultiThreadDictionary<Key: Hashable, Value> {
+    private let name: String
+    private var dict = [Key: Value]()
+    private let queue: DispatchQueue
+    
+    init(name: String) {
+        self.name = name
+        self.queue = DispatchQueue(label: "MultiThreadDictionary (\(name)) Coordinator", attributes: .concurrent)
+    }
+    
+    subscript(key: Key) -> Value? {
+        get {
+            var result: Value? = nil
+            queue.sync {
+                result = dict[key]
+            }
+            return result
+        }
+        set(value) {
+            queue.async(flags: .barrier) {
+                self.dict[key] = value
+            }
+        }
+    }
+    
+    func removeValueWithoutReturning(forKey key: Key) {
+        queue.async(flags: .barrier) {
+            self.dict.removeValue(forKey: key)
+        }
+    }
+    
+    /// If the result of this function is unused, it is preferable to use `removeValueWithoutReturning` as it executes asynchronously and doesn't block the calling thread.
+    func removeValue(forKey key: Key) -> Value? {
+        var value: Value? = nil
+        queue.sync(flags: .barrier) {
+            value = dict.removeValue(forKey: key)
+        }
+        return value
+    }
+}

Tusker/Views/AccountDisplayNameLabel.swift

@@ -41,7 +41,7 @@ struct AccountDisplayNameLabel<Account: AccountProtocol>: View {
         let matches = emojiRegex.matches(in: account.displayName, options: [], range: fullRange)
         guard !matches.isEmpty else { return }
         
-        let emojiImages = CachedDictionary<Image>(name: "AcccountDisplayNameLabel Emoji Images")
+        let emojiImages = MultiThreadDictionary<String, Image>(name: "AcccountDisplayNameLabel Emoji Images")
         
         let group = DispatchGroup()
         

Tusker/Views/ContentTextView.swift

@@ -51,7 +51,7 @@ class ContentTextView: LinkTextView {
     func setEmojis(_ emojis: [Emoji]) {
         guard !emojis.isEmpty else { return }
         
-        let emojiImages = CachedDictionary<UIImage>(name: "ContentTextView Emoji Images")
+        let emojiImages = MultiThreadDictionary<String, UIImage>(name: "ContentTextView Emoji Images")
         
         let group = DispatchGroup()
         

Tusker/Views/EmojiLabel.swift

@@ -26,7 +26,7 @@ class EmojiLabel: UILabel {
         let matches = emojiRegex.matches(in: attributedText.string, options: [], range: attributedText.fullRange)
         guard !matches.isEmpty else { return }
         
-        let emojiImages = CachedDictionary<UIImage>(name: "EmojiLabel Emoji Images")
+        let emojiImages = MultiThreadDictionary<String, UIImage>(name: "EmojiLabel Emoji Images")
         
         let group = DispatchGroup()