Make fetching all unread counts an operation. Cancel it when the account is suspending. Turning things like this into operations goes to fixing the dreaded 0xdead10cc crashes.

Frameworks/Account/Account.swift

@@ -231,6 +231,11 @@ public final class Account: DisplayNameProvider, UnreadCountProvider, Container,
 		return delegate.refreshProgress
 	}
 
+	private var operationQueue = MainThreadOperationQueue()
+	private enum OperationName {
+		static let FetchAllUnreadCounts = "FetchAllUnreadCounts"
+	}
+	
 	init?(dataFolder: String, type: AccountType, accountID: String, transport: Transport? = nil) {
 		switch type {
 		case .onMyMac:
@@ -414,6 +419,8 @@ public final class Account: DisplayNameProvider, UnreadCountProvider, Container,
 	}
 	
 	public func suspendDatabase() {
+		operationQueue.suspend()
+		cancelDiscardableOperations()
 		database.suspend()
 		save()
 		metadataFile.suspend()
@@ -426,6 +433,7 @@ public final class Account: DisplayNameProvider, UnreadCountProvider, Container,
 	public func resumeDatabaseAndDelegate() {
 		database.resume()
 		delegate.resume()
+		operationQueue.resume()
 	}
 
 	/// Reload OPML, etc.
@@ -448,6 +456,10 @@ public final class Account: DisplayNameProvider, UnreadCountProvider, Container,
 		delegate.accountWillBeDeleted(self)
 	}
 
+	public func cancelDiscardableOperations() {
+		operationQueue.cancelOperations(named: OperationName.FetchAllUnreadCounts)
+	}
+	
 	func loadOPMLItems(_ items: [RSOPMLItem], parentFolder: Folder?) {
 		var feedsToAdd = Set<WebFeed>()
 
@@ -1226,24 +1238,31 @@ private extension Account {
 
 	func fetchAllUnreadCounts() {
 		fetchingAllUnreadCounts = true
+		operationQueue.cancelOperations(named: OperationName.FetchAllUnreadCounts)
 
-		database.fetchAllNonZeroUnreadCounts { (unreadCountDictionaryResult) in
-			if let unreadCountDictionary = try? unreadCountDictionaryResult.get() {
-				self.flattenedWebFeeds().forEach{ (feed) in
-					// When the unread count is zero, it won’t appear in unreadCountDictionary.
-					if let unreadCount = unreadCountDictionary[feed.webFeedID] {
-						feed.unreadCount = unreadCount
-					}
-					else {
-						feed.unreadCount = 0
-					}
+		let operation = database.createFetchAllUnreadCountsOperation()
+		operation.name = OperationName.FetchAllUnreadCounts
+		operation.completionBlock = { operation in
+			let fetchOperation = operation as! FetchAllUnreadCountsOperation
+			guard let unreadCountDictionary = fetchOperation.unreadCountDictionary else {
+				return
 			}
+			self.processUnreadCounts(unreadCountDictionary: unreadCountDictionary)
 
 			self.fetchingAllUnreadCounts = false
 			self.updateUnreadCount()
 			self.isUnreadCountsInitialized = true
 			self.postUnreadCountDidInitializeNotification()
 		}
+
+		operationQueue.addOperation(operation)
+	}
+
+	func processUnreadCounts(unreadCountDictionary: UnreadCountDictionary) {
+		for feed in flattenedWebFeeds() {
+			// When the unread count is zero, it won’t appear in unreadCountDictionary.
+			let unreadCount = unreadCountDictionary[feed.webFeedID] ?? 0
+			feed.unreadCount = unreadCount
 		}
 	}
 }

Frameworks/ArticlesDatabase/ArticlesDatabase.swift

@@ -141,10 +141,6 @@ public final class ArticlesDatabase {
 		articlesTable.fetchUnreadCounts(webFeedIDs, completion)
 	}
 
-	public func fetchAllNonZeroUnreadCounts(_ completion: @escaping UnreadCountDictionaryCompletionBlock) {
-		articlesTable.fetchAllUnreadCounts(completion)
-	}
-
 	public func fetchUnreadCountForToday(for webFeedIDs: Set<String>, completion: @escaping SingleUnreadCountCompletionBlock) {
 		fetchUnreadCount(for: webFeedIDs, since: todayCutoffDate(), completion: completion)
 	}
@@ -195,6 +191,13 @@ public final class ArticlesDatabase {
 		articlesTable.createStatusesIfNeeded(articleIDs, completion)
 	}
 
+	// MARK: - Operations
+
+	/// Create and return an operation that fetches all non-zero unread counts.
+	public func createFetchAllUnreadCountsOperation() -> FetchAllUnreadCountsOperation {
+		return articlesTable.createFetchAllUnreadCountsOperation()
+	}
+
 	// MARK: - Suspend and Resume (for iOS)
 
 	/// Close the database and stop running database calls.

Frameworks/ArticlesDatabase/ArticlesTable.swift

@@ -521,6 +521,10 @@ final class ArticlesTable: DatabaseTable {
 			}
 		}
 	}
+
+	func createFetchAllUnreadCountsOperation() -> FetchAllUnreadCountsOperation {
+		return FetchAllUnreadCountsOperation(databaseQueue: queue, cutoffDate: articleCutoffDate)
+	}
 }
 
 // MARK: - Private

Frameworks/ArticlesDatabase/Operations/FetchAllUnreadCountsOperation.swift

@@ -10,16 +10,16 @@ import Foundation
 import RSCore
 import RSDatabase
 
-final class FetchAllUnreadCountsOperation: MainThreadOperation {
+public final class FetchAllUnreadCountsOperation: MainThreadOperation {
 
 	public var unreadCountDictionary: UnreadCountDictionary?
 
 	// MainThreadOperation
-	var isCanceled = false
-	var id: Int?
-	weak var operationDelegate: MainThreadOperationDelegate?
-	var name: String? = "FetchAllUnreadCountsOperation"
-	var completionBlock: MainThreadOperation.MainThreadOperationCompletionBlock?
+	public var isCanceled = false
+	public var id: Int?
+	public weak var operationDelegate: MainThreadOperationDelegate?
+	public var name: String?
+	public var completionBlock: MainThreadOperation.MainThreadOperationCompletionBlock?
 
 	private let queue: DatabaseQueue
 	private let cutoffDate: Date
@@ -29,7 +29,7 @@ final class FetchAllUnreadCountsOperation: MainThreadOperation {
 		self.cutoffDate = cutoffDate
 	}
 	
-	func run() {
+	public func run() {
 		queue.runInDatabase { databaseResult in
 			if self.isCanceled {
 				self.informOperationDelegateOfCompletion()
@@ -48,14 +48,6 @@ final class FetchAllUnreadCountsOperation: MainThreadOperation {
 
 private extension FetchAllUnreadCountsOperation {
 
-	func informOperationDelegateOfCompletion() {
-		DispatchQueue.main.async {
-			if !self.isCanceled {
-				self.operationDelegate?.operationDidComplete(self)
-			}
-		}
-	}
-
 	func fetchUnreadCounts(_ database: FMDatabase) {
 		let sql = "select distinct feedID, count(*) from articles natural join statuses where read=0 and userDeleted=0 and (starred=1 or dateArrived>?) group by feedID;"