[#435] thread sanitizer issues (#448)

* [#435] this commit attempts to fix thread being starved dues to inversion
of priorities where a .userInitiated thread ends up depending on a lower
priority one on GRPC.

* Add an Synchronizer State struct to report state at once

* Make CompactBlockProcessor's downloader available internally for SDKSynchronizer
remove duplicate handling of processor finished

* PR Suggestions

Sources/ZcashLightClientKit/Block/DatabaseStorage/CompactBlockStorage.swift

@@ -86,7 +86,7 @@ extension CompactBlockStorage: CompactBlockRepository {
     }
     
     func latestHeight(result: @escaping (Swift.Result<BlockHeight, Error>) -> Void) {
-        DispatchQueue.global(qos: .userInitiated).async {
+        DispatchQueue.global(qos: .default).async {
             do {
                 result(.success(try self.latestBlockHeight()))
             } catch {
@@ -100,7 +100,7 @@ extension CompactBlockStorage: CompactBlockRepository {
     }
     
     func write(blocks: [ZcashCompactBlock], completion: ((Error?) -> Void)?) {
-        DispatchQueue.global(qos: .userInitiated).async {
+        DispatchQueue.global(qos: .default).async {
             do {
                 try self.insert(blocks)
                 completion?(nil)
@@ -111,7 +111,7 @@ extension CompactBlockStorage: CompactBlockRepository {
     }
     
     func rewind(to height: BlockHeight, completion: ((Error?) -> Void)?) {
-        DispatchQueue.global(qos: .userInitiated).async {
+        DispatchQueue.global(qos: .default).async {
             do {
                 try self.rewind(to: height)
                 completion?(nil)

Sources/ZcashLightClientKit/Block/Processor/CompactBlockProcessor.swift

@@ -322,9 +322,11 @@ public class CompactBlockProcessor {
             self.stop()
         }
     }
+
     var maxAttemptsReached: Bool {
         self.retryAttempts >= self.config.retries
     }
+
     var shouldStart: Bool {
         switch self.state {
         case .stopped, .synced, .error:
@@ -335,7 +337,7 @@ public class CompactBlockProcessor {
     }
 
     private var service: LightWalletService
-    private var downloader: CompactBlockDownloading
+    private(set) var downloader: CompactBlockDownloading
     private var storage: CompactBlockStorage
     private var transactionRepository: TransactionRepository
     private var accountRepository: AccountRepository
@@ -1130,7 +1132,8 @@ public class CompactBlockProcessor {
         case .downloading:
             NotificationCenter.default.post(name: Notification.Name.blockProcessorStartedDownloading, object: self)
         case .synced:
-            NotificationCenter.default.post(name: Notification.Name.blockProcessorFinished, object: self)
+            // transition to this state is handled by `processingFinished(height: BlockHeight)`
+            break
         case .error(let err):
             notifyError(err)
         case .scanning:
@@ -1396,7 +1399,7 @@ extension CompactBlockProcessor {
             queue: DispatchQueue?,
             result: @escaping (Result<FigureNextBatchOperation.NextState, Error>) -> Void
         ) {
-            let dispatchQueue = queue ?? DispatchQueue.global(qos: .userInitiated)
+            let dispatchQueue = queue ?? DispatchQueue.global(qos: .default)
             
             dispatchQueue.async {
                 do {

Sources/ZcashLightClientKit/DAO/PagedTransactionDao.swift

@@ -50,7 +50,7 @@ class PagedTransactionDAO: PaginatedTransactionRepository {
     }
     
     func page(_ number: Int, result: @escaping (Result<[TransactionEntity]?, Error>) -> Void) {
-        DispatchQueue.global(qos: .userInitiated).async { [weak self] in
+        DispatchQueue.global(qos: .default).async { [weak self] in
             guard let self = self else { return }
             do {
                 result(.success(try self.page(number)))

Sources/ZcashLightClientKit/Synchronizer/SDKSynchronizer.swift

@@ -77,6 +77,12 @@ public extension Notification.Name {
 /// Synchronizer implementation for UIKit and iOS 12+
 // swiftlint:disable type_body_length
 public class SDKSynchronizer: Synchronizer {
+    public struct SynchronizerState {
+        public var shieldedBalance: WalletBalance
+        public var transparentBalance: WalletBalance
+        public var syncStatus: SyncStatus
+        public var latestScannedHeight: BlockHeight
+    }
 
     public enum NotificationKeys {
         public static let progress = "SDKSynchronizer.progress"
@@ -89,6 +95,7 @@ public class SDKSynchronizer: Synchronizer {
         public static let nextStatus = "SDKSynchronizer.nextStatus"
         public static let currentConnectionState = "SDKSynchronizer.currentConnectionState"
         public static let previousConnectionState = "SDKSynchronizer.previousConnectionState"
+        public static let synchronizerState = "SDKSynchronizer.synchronizerState"
     }
     
     public private(set) var status: SyncStatus {
@@ -435,16 +442,12 @@ public class SDKSynchronizer: Synchronizer {
     }
     
     @objc func processorFinished(_ notification: Notification) {
-        // FIX: Pending transaction updates fail if done from another thread. Improvement needed: explicitly define queues for sql repositories
+        // FIX: Pending transaction updates fail if done from another thread. Improvement needed: explicitly define queues for sql repositories see: https://github.com/zcash/ZcashLightClientKit/issues/450
-            
+        if let blockHeight = notification.userInfo?[CompactBlockProcessorNotificationKey.latestScannedBlockHeight] as? BlockHeight {
-            DispatchQueue.main.async { [weak self] in
+            self.latestScannedHeight = blockHeight
-                guard let self = self else { return }
+        }
-                if let blockHeight = notification.userInfo?[CompactBlockProcessorNotificationKey.latestScannedBlockHeight] as? BlockHeight {
+        self.refreshPendingTransactions()
-                    self.latestScannedHeight = blockHeight
+        self.status = .synced
-                }
-                self.refreshPendingTransactions()
-                self.status = .synced
-            }
     }
     
     @objc func processorTransitionUnknown(_ notification: Notification) {
@@ -624,15 +627,15 @@ public class SDKSynchronizer: Synchronizer {
     }
     
     public func latestDownloadedHeight() throws -> BlockHeight {
-        try initializer.downloader.lastDownloadedBlockHeight()
+        try blockProcessor.downloader.lastDownloadedBlockHeight()
     }
     
     public func latestHeight(result: @escaping (Result<BlockHeight, Error>) -> Void) {
-        initializer.downloader.latestBlockHeight(result: result)
+        blockProcessor.downloader.latestBlockHeight(result: result)
     }
     
     public func latestHeight() throws -> BlockHeight {
-        try initializer.downloader.latestBlockHeight()
+        try blockProcessor.downloader.latestBlockHeight()
     }
     
     public func latestUTXOs(address: String, result: @escaping (Result<[UnspentTransactionOutputEntity], Error>) -> Void) {
@@ -770,7 +773,16 @@ public class SDKSynchronizer: Synchronizer {
                 name: Notification.Name.synchronizerSynced,
                 object: self,
                 userInfo: [
-                    SDKSynchronizer.NotificationKeys.blockHeight: self.latestScannedHeight
+                    SDKSynchronizer.NotificationKeys.blockHeight: self.latestScannedHeight,
+                    SDKSynchronizer.NotificationKeys.synchronizerState: SynchronizerState(
+                        shieldedBalance: WalletBalance(
+                            verified: initializer.getVerifiedBalance(),
+                            total: initializer.getBalance()
+                        ),
+                        transparentBalance: (try? self.getTransparentBalance(accountIndex: 0)) ?? WalletBalance.zero,
+                        syncStatus: status,
+                        latestScannedHeight: self.latestScannedHeight
+                    )
                 ]
             )
         case .unprepared:

Sources/ZcashLightClientKit/Transaction/PersistentTransactionManager.swift

@@ -35,7 +35,7 @@ class PersistentTransactionManager: OutboundTransactionManager {
         self.encoder = encoder
         self.service = service
         self.network = networkType
-        self.queue = DispatchQueue.init(label: "PersistentTransactionManager.serial.queue", qos: .userInitiated)
+        self.queue = DispatchQueue.init(label: "PersistentTransactionManager.serial.queue", qos: .default)
     }
     
     func initSpend(

Tests/TestUtils/FakeService.swift

@@ -111,7 +111,7 @@ class MockLightWalletService: LightWalletService {
     }
     
     func submit(spendTransaction: Data, result: @escaping (Result<LightWalletServiceResponse, LightWalletServiceError>) -> Void) {
-        DispatchQueue.global(qos: .userInitiated).asyncAfter(deadline: .now() + 1) {
+        DispatchQueue.global(qos: .default).asyncAfter(deadline: .now() + 1) {
             result(.success(LightWalletServiceMockResponse(errorCode: 0, errorMessage: "", unknownFields: UnknownStorage())))
         }
     }