Swift Concurrency Resources: DevForums tags: Concurrency The Swift Programming Language Concurrency > Concurrency documentation WWDC 2022 Session 110351 Eliminate data races using Swift Concurrency — This ‘sailing on the sea of concurrency’ talk is a great introduction to the fundamentals. WWDC 2021 Session 10134 Explore structured concurrency in Swift — The table that starts rolling out at around 25:45 is really helpful. Dispatch Resources: DevForums tags: Dispatch Dispatch documentation — Note that the Swift API and C API, while generally aligned, are different in many details. Make sure you select the right language at the top of the page. Dispatch man pages — While the standard Dispatch documentation is good, you can still find some great tidbits in the man pages. See Reading UNIX Manual Pages. Start by reading dispatch in section 3. WWDC 2015 Session 718 Building Responsive and Efficient Apps with GCD [1] WWDC 2017 Session 706 Modernizing Grand Central Dispatch Usage [1] Avoid Dispatch Global Concurrent Queues DevForums post Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" [1] These videos may or may not be available from Apple. If not, the URL should help you locate other sources of this info.

I have folder monitoring code using makeFileSystemObjectSource. The events are triggered for everything else, but not for when I edit a file with nano terminal command. Am I doing something wrong? Is it a bug? Is this intended and unfixable? Code sample: monitoredFolderFileDescriptor = open(currentlyMonitoredPath, O_EVTONLY) folderMonitorSource = DispatchSource.makeFileSystemObjectSource(fileDescriptor: monitoredFolderFileDescriptor, eventMask: .all, queue: .main) folderMonitorSource?.setEventHandler { // ... } folderMonitorSource?.setCancelHandler { // ... } folderMonitorSource?.resume()

class CalculatorViewModel : NSObject, ObservableObject, Identifiable { var id = UUID() @Published var output = "Disconnected" @Published var connected = false @Published var databasePath = String() enum itemType : Int{ case angle = 1 case degree = 2 case grip1 = 3 case grip2 = 4 } struct test_Array: Identifiable { var id = UUID() var time: String var swingNum : Int var dataSeqInSwing: Int var timeStampInSeq: Double var itemType: Int var value: Double } @Published var testDBdata = [test_Array] () ..... private var centralManager: CBCentralManager? func connectCalculator() { output = "Connecting..." centralQueue = DispatchQueue(label: "test.discovery") centralManager = CBCentralManager(delegate: self, queue: centralQueue) } .... func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) { ..... if characteristic.uuid == outputCharUUID, var data = characteristic.value { ..... DispatchQueue.main.async() { for index in tupleSets { strItemSets = index.components(separatedBy: ",") ....... var itemN = 1 for indexStr in strItemSets { self.golfDBdata[numDB].dataSeqInSwing = countItem. <= Error self.golfDBdata[numDB].itemType = itemN self.golfDBdata[numDB].value = Double(strItemSets[itemN]) ?? 0.0

A handful of my customers have reported a consistent freeze in my app (smells like either a thread deadlock or an infinite recursion to me). It's working properly for most people, but if 3 people are reporting it to me that says to me that probably 300 are experiencing it but staying quiet. It happens every time they take a certain kind of action. But it never happens to me so I can't figure out what is breaking. No crash is happening, so I'm not getting any reports via Firebase. It doesn't appear to be related to their data, because they can have someone else use a different device, login to their account, download all of their data, and then successfully do the thing that freezes 100% of the time on their original device. I've got one of these customers set up on TestFlight so I can send them test versions of the app with some debug collection code. I created my own version of a tracelog and write a line to a file whenever I start/end a function. I've added those tracelog calls to a bunch of methods and classes (but not all). The action that causes the freeze is when they tap Edit on a record. What's supposed to happen is that I modally present a nav controller containing an EditBlahViewController. The trace logs show that the EditBlahViewController gets through viewDidLoad, viewWillAppear, two rounds of viewWillLayoutSubviews/viewDidLayoutSubviews... but then never gets to viewDidAppear. I've tried updating more and more functions/classes with the tracelog calls, but I can't find any infinite recursions. I've added tracelogs to all calls involving dispatching to other threads (especially synchronous dispatches to the main thread) but I don't see any deadlocks. Every dispatch to main starts and ends properly and then goes on to the next thing. User is on iOS 16.6.1 with an iPhone 12. I don't know what else to try. How can I debug this at a distance and figure out where the problem is?

Hi! I have a xcode workspace with first objectiveC framework (let’s call it framework#1). This framework has some singletons (+(instancetype)shared using the dispatch_once idiom. This code is pretty straight forward and used everywhere : + (instancetype)shared { static dispatch_once_t onceToken; static OGAKeyManager *instance = nil; dispatch_once(&onceToken, ^{ instance = [[self alloc] init]; }); return instance; } I have a second framework (framework#2) in Swift that uses theses singletons (the framework#1 is added as do not embeed in the framework settings). And I have an application that uses both frameworks. If I make a breakpoint inside the dispatch_once alloc/init, I see that I enter 2 times : once when the shared method is called from framework#1 and another one when it’s called from framework#2. How is that even possible ? Isn't dispatch_once supposed to handle this ? I asked chatGPT, it points out to some objC/Swift interoperability, but honestly, I don't see what I can do to make it work correctly. There is no circular dependency (framwork#2 uses framwork#1, but framwork#1 has no clue of framwork#2 existence) Maybe it has something to do with sandbox, but I don't see how can it be. Does anyone experienced some weird behavior like this ? Thanks

In a thread titled “Avoid Dispatch Global Concurrent Queues” [1], Quinn links to a video from WWDC 2015 Session 718, “Building Responsive and Efficient Apps with GCD”. However, this video is not available from the Apple Developer Videos site; only a half dozen or so videos from 2015 are available. This same issue of the missing video came up about five years ago, when Quinn stated that the video had been mistakenly removed but had been restored. Now it’s gone again. :sad_face: Could this video be restored again, or at least its transcript? While I understand that Apple is focused on Swift concurrency, I need to maintain some Objective-C code that uses GCD, and in tracking down some performance issues, I would like to better understand the tradeoffs in the existing code and make improvements where I can. I don’t have the resources to reimplement the code in Swift right now. (More generally, why can't Apple just leave all these videos online indefinitely, for historical purposes at least? Couldn't the ones deemed “old and misleading” just be tagged with a banner like the legacy documentation has?) [1] I like to think of these valuable threads as “Quinn Technical Notes”; I have a page in my Notes app that holds links to the ones I’ve found.

I had 2 crash report from our customer. Both crash point is same but there is no my code on crash stack trace. How to fix this kind of crash problem. Thread 1 Crashed:: Dispatch queue: com.apple.root.background-qos 0 libsystem_kernel.dylib 0x7ff81b84922a __pthread_kill + 10 1 libsystem_pthread.dylib 0x7ff81b880f7b pthread_kill + 263 2 libsystem_c.dylib 0x7ff81b7caca5 abort + 123 3 libc++abi.dylib 0x7ff81b83b082 abort_message + 241 4 libc++abi.dylib 0x7ff81b82c23d demangling_terminate_handler() + 266 5 libobjc.A.dylib 0x7ff81b529023 _objc_terminate() + 96 6 libc++abi.dylib 0x7ff81b83a4a5 std::__terminate(void (*)()) + 8 7 libc++abi.dylib 0x7ff81b83a456 std::terminate() + 54 8 libdispatch.dylib 0x7ff81b701a58 _dispatch_client_callout + 28 9 libdispatch.dylib 0x7ff81b704500 _dispatch_continuation_pop + 463 10 libdispatch.dylib 0x7ff81b715dff _dispatch_source_invoke + 2184 11 libdispatch.dylib 0x7ff81b7116a2 _dispatch_root_queue_drain + 343 12 libdispatch.dylib 0x7ff81b711e4d _dispatch_worker_thread2 + 160 13 libsystem_pthread.dylib 0x7ff81b87dc9d _pthread_wqthread + 256 14 libsystem_pthread.dylib 0x7ff81b87cc67 start_wqthread + 15 This crash point is exactly same with this post. I do not throw C++ exception. https://developer.apple.com/forums/thread/725197

I see this warning when my app runs: Thread running at QOS_CLASS_USER_INTERACTIVE waiting on a lower QoS thread running at QOS_CLASS_DEFAULT. Investigate ways to avoid priority inversions This is true; I know what is going on. I'd like this other thread to have a higher priority. But how do I set the "QOS class" for a thread? Searching developer.apple.com for QOS_CLASS_USER_INTERACTIVE doesn't find much. It seems that dispatch queues have priorities, but in this case I have a thread, not a dispatch queue. Any ideas?