Processes & Concurrency

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best practices for communication between system extension and daemon
Hello, My team has developed a DNS proxy for macOS. We have this set up with a system extension that interacts with the OS, and an always-running daemon that does all the heavy lifting. Communication between the two is DNS request and response packet traffic. With this architecture what are best practices for how the system extension communicates with a daemon? We tried making the daemon a socket server, but the system extension could not connect to it. We tried using XPC but it did not work and we could not understand the errors that were returned. So what is the best way to do this sort of thing?
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751
Jan ’25
Effect of app nap of Timer
I'm developing a macOS application that tracks the duration of a user's session using a timer, which is displayed both in the main window and in an menu bar extra view. I have a couple of questions regarding the timer's behavior: What happens to the timer if the user closes the application's window (causing the app to become inactive) but does not fully quit it? Does the timer continue to run, pause, or behave in some other way? Will the app nap feature stop the timer when app is in-active state? When the application is inactive and the system is either in sleep mode or locked, does the timer’s tolerance get affected? In other words, will the timer fire with any additional delay compared to its scheduled time under these conditions?
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79
Mar ’25
Alternatives to com.apple.security.temporary-exception.apple-events: com.apple.Terminal ?
Hello 👋 Our team added com.apple.security.temporary-exception.apple-events: com.apple.Terminal recently to our Mac app to be able to tell the terminal to execute a specific command line automatically for the user when clicking a button but we've been rejected during review because of this entitlement so for now we've deleted it and deleted the associated feature. It concerns the following feature (see attachment). Context: Among other things the application enable to review pull request changes (remote) and we would like a button to automatically clone the pull request on disk when user click a button. We would like to use terminal for security reason as when cloning using git command we need ssh keys or other credential and there's no reason (rather than technical ones) that the user provide us such private information that is stored in the ~/.ssh. We prefer think the other way around and tell the user what to execute instead (no credentials involved or shared). We referred to: https://developer.apple.com/library/archive/documentation/Miscellaneous/Reference/EntitlementKeyReference/Chapters/AppSandboxTemporaryExceptionEntitlements.html I admit it's unclear for me if this will imply a 100% rejection or if these entitlements are deprecated. Is "com.apple.security.temporary-exception.apple-events: com.apple.Terminal" an entitlement that is reserved for special Apple partners ? Is it an entitlement that we should demonstrate usage first ? Or should we completely remove the feature if we distribute through the App Store ? Is Apple advice for other APIs to develop such features (execute command line for the user) when distributing through the App Store ? As said we've disabled the feature for now. Thank you in advance for those who will take time to answer this,
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148
Jul ’25
System Network Extension XPC with LaunchAgent
I've discovered that a system network extension can communicate with a LaunchDaemon (loaded using SMAppService) over XPC, provided that the XPC service name begins with the team ID. If I move the launchd daemon plist to Contents/Library/LaunchAgents and swap the SMAppService.daemon calls to SMAppService.agent calls, and remove the .privileged option to NSXPCConnection, the system extension receives "Couldn't communicate with a helper application" as an error when trying to reach the LaunchAgent advertised service. Is this limitation by design? I imagine it is, but wanted to check before I spent any more time on it.
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221
Jul ’25
Using raise in GCD can cause timing issues with the signal mechanism.
when we use raise in GCD, the signal handler is executed asynchronously, whereas in pthread, it is executed synchronously as expected. example: #include <Foundation/Foundation.h> #include <pthread/pthread.h> static void HandleSignal(int sigNum, siginfo_t* signalInfo, void* userContext) { printf("handle signal %d\n", sigNum); printf("begin sleep\n"); sleep(3); printf("end sleep\n"); } void InstallSignal(void) { static const int g_fatalSignals[] = { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGPIPE, SIGSEGV, SIGSYS, SIGTRAP, }; int fatalSignalsCount = sizeof(g_fatalSignals) / sizeof(int); struct sigaction action = {{0}}; action.sa_flags = SA_SIGINFO | SA_ONSTACK; #if defined(__LP64__) action.sa_flags |= SA_64REGSET; #endif sigemptyset(&action.sa_mask); action.sa_sigaction = &HandleSignal; struct sigaction pre_sa; for(int i = 0; i < fatalSignalsCount; i++) { int sigResult = sigaction(g_fatalSignals[i], &action, &pre_sa); } } void* RaiseAbort(void *userdata) { raise(SIGABRT); printf("signal handler has finished\n"); return NULL; } int main(int argc, const char * argv[]) { InstallSignal(); dispatch_async(dispatch_get_global_queue(0, 0), ^{ raise(SIGABRT); // abort(); // abort() is ok RaiseAbort(nullptr); }); // pthread is ok // pthread_t tid; // int ret = pthread_create(&tid, NULL, RaiseAbort, NULL); // if (ret != 0) { // fprintf(stderr, "create thread failed\n"); // return EXIT_FAILURE; // } [[NSRunLoop mainRunLoop] run]; return 0; } console log: signal handler has finished handle signal 6 begin sleep end sleep
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222
Sep ’25
Launch constraints using LightweightCodeRequirements framework
MacOS Version: 14.7.2 macOS SDKs: macOS 14.5 -sdk macosx14.5 I am working on a sample program for validation Against: Team Identifier Developer ID I started with validating Team Identifier, but my validation is not working and it is allowing to launch programs which are not matching the team identifier in the signature. Below is my code: func verifyExecutableWithLCR(executablePath: String, arguments: [String]) -> Bool { let task = Process() task.launchPath = executablePath task.arguments = arguments if #available(macOS 14.4, *) { print("launchRequirementData is available on this system.") do { let req = try OnDiskCodeRequirement.allOf { TeamIdentifier("ABCDEFGHI") //SigningIdentifier("com.***.client.***-Client.****") } let encoder = PropertyListEncoder() encoder.outputFormat = .xml let requirementData = try encoder.encode(req) task.launchRequirementData = requirementData print("launchRequirementData is set.") try task.run() print("[SUCCESS] Executable passed the code signature verification.") return true } catch { print("[ERROR] Code signature verification failed: \(error.localizedDescription)") return false } } else { print("[WARNING] launchRequirement is not available on this macOS version.") return false } } Could you please help me in identifying whay am I doing wrong here?
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569
Feb ’25
SMAppService - How does this work?
I'm a developer using Lazarus Pascal, so converting ObjC and Swift comes with its challenges. I'm trying to figure how to properly use SMAppService to add my application as a login item for the App Store. I have learned that the old method (< macOS 13) uses a helper tool, included in the app bundle, which calls the now deprecated SMLoginItemSetEnabled. Now this is already quite a pain to deal with if you're not using XCode, not to mention converting the headers being rather complicated when you're not experienced with doing this. The "new" method (as of macOS 13) is using SMAppService. Can anyone explain how to use this? The documentation (for me anyway) is a not very clear about that and neither are examples that can be found all over the Internet. My main question is: Can I now use the SMAppService functions to add/remove a login item straight in my application, or is a helper tool still required?
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161
Mar ’25
Reliable 30-minute background data fetching for safety-critical monitoring app?
I'm developing a safety-critical monitoring app that needs to fetch data from government APIs every 30 minutes and trigger emergency audio alerts for threshold violations. The app must work reliably in background since users depend on it for safety alerts even while sleeping. Main Challenge: iOS background limitations seem to prevent consistent 30-minute intervals. Standard BGTaskScheduler and timers get suspended after a few minutes in background. Question: What's the most reliable approach to ensure consistent 30-minute background monitoring for a safety-critical app where missed alerts could have serious consequences? Are there special entitlements or frameworks for emergency/safety applications? The app needs to function like an alarm clock - working reliably even when backgrounded with emergency audio override capabilities.
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548
Jul ’25
App being launched while device is locked
DESCRIPTION OF PROBLEM Logs and data from our application indicate various errors that strongly suggest that our application is being launched in a state in which the device is likely locked. We are looking for guidance on how to identify, debug, reproduce, and fix these cases. Our application does not use any of the common mechanisms for background activity, such as Background App Refresh, Navigation, Audio, etc. Errors we get in our logs such as "authorization denied (code: 23)" when trying to access a file in our app's container on disk (a simple disk cache for data our application uses) strongly suggest that the device is operating in a state, such as being locked, where our application lacks the requisite permissions it would normally have during operation. Furthermore, attempts to access authentication information stored in the keychain also fails. We use kSecAttrAccessibleWhenUnlocked when accessing items we store in the keychain. We have investigated "Prewarming", as well as our notification extension that helps process incoming push notifications, but cannot find any way to recreate this behavior. Are there any steps Apple engineers can recommend to triage and debug this? Some additional questions that would help us: What are all of the symptoms that we can look for if prewarming escapes the intended execution context? What are all of the circumstances in which we would be unauthorized to access the app’s documents/file directories even if it works correctly in normal operation? STEPS TO REPRODUCE Unfortunately, we are unable to forcibly reproduce this behavior in our application, so we're looking for guidance on how we might simulate this behavior in Xcode / Instruments. Are there tools that Apple provides that would allow us to simulate certain behaviors like prewarming to verify our application's functionality? Are there other reasons our application might be launched while the device is locked? Are there other reasons we would receive security errors when accessing the keychain or disk that are unrelated to the device being locked?
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576
Jan ’25
[iOS 26 Beta] BGTaskScheduler.supportedResources incorrectly reports no GPU support for BGContinuedProcessingTask on capable hardware
Testing Environment: iOS: 26.0 Beta 7 Xcode: Beta 6 Description: We are implementing the new BGContinuedProcessingTask API introduced in iOS 26. We have followed the official documentation and WWDC session guidance to configure our project. The Background Modes (processing) and Background GPU Access capabilities have been added in Xcode. The com.apple.developer.background-tasks.continued-processing.gpu entitlement is present and set to in the .entitlements file. The provisioning profile details viewed within Xcode explicitly show that the "Background GPU Access" capability and the corresponding entitlement are included. Despite this correct configuration, when running the app on supported hardware (iPhone 16 Pro), a call to BGTaskScheduler.supportedResources.contains(.gpu) consistently returns false. This prevents us from setting request.requiredResources = .gpu. As a result, when the BGContinuedProcessingTask starts without the GPU resource flag, our internal Metal-based exporter attempts to access the GPU and is terminated by the system, throwing an IOGPUMetalError: Insufficient Permission (to submit GPU work from background). We have performed extensive debugging, including a full reset of the provisioning profile (removing/re-adding capabilities, toggling automatic signing, cleaning build folders, and reinstalling the app), but the issue persists. This strongly suggests a bug in the iOS 26 beta where the runtime is failing to correctly validate a valid entitlement. Additionally, we've observed inconsistent behavior across devices. On an A16-based iPad, the task submits successfully (BGTaskScheduler.submit does not throw an error), but the launch handler is never invoked by the system. On the iPhone 16 Pro, the handler is invoked, but we encounter the supportedResources issue described above. This leads us to ask for clarification on the exact hardware requirements for this feature. We hypothesize that it may be limited to devices that support Apple Intelligence (A17 Pro and newer). Could you please confirm this and provide official documentation on the device support criteria? Steps to Reproduce: Create a new Xcode project. In Signing & Capabilities, add "Background Modes" (with "Background processing" checked) and "Background GPU Access". Add a permitted identifier (e.g., "com.company.test.*") to BGTaskSchedulerPermittedIdentifiers in Info.plist. In application(_:didFinishLaunchingWithOptions:) or a ViewController's viewDidLoad, log the result of BGTaskScheduler.shared.supportedResources.contains(.gpu). Build and run on a physical, supported device (e.g., iPhone 16 Pro). Expected Results: The log should indicate that BGTaskScheduler.shared.supportedResources.contains(.gpu) returns true. Actual Results: The log shows that BGTaskScheduler.shared.supportedResources.contains(.gpu) returns false.
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2w
XPC - performance/load testing
I have an XPC server running on macOS and want to perform comprehensive performance and load testing to evaluate its efficiency, responsiveness, and scalability. Specifically, I need to measure factors such as request latency, throughput, and how well it handles concurrent connections under different load conditions. What are the best tools, frameworks, or methodologies for testing an XPC service? Additionally, are there any best practices for simulating real-world usage scenarios and identifying potential bottlenecks?
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137
Apr ’25
Stay connected to Medical BLE device in background
I work for a large medical device company. We have a 1st party BLE enabled medical device that must be very battery efficient. To this end, if a connection is lost, the BLE radio is powered down after 60 seconds and will only turn back on when a physical button on the device is pressed. I've been tasked with connecting to the device, staying connected to the device, and being able to retrieve data from the device upon a timed action. For instance, this could include a data read and transmission while they sleep. The key part of this is staying reliably connected for extended periods of time. This is a BYOD setup, and we cannot control power profiles. I would very much appreciate any information, recommendations, and/or insights into solving this problem. Thanks!
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352
Sep ’25
EXC_BREAKPOINT in BGAppRefreshTask
When I run my app with XCode on my iPhone, and then moved into the background, I'm getting a EXC_BREAKPOINT exception after a few minutes, seemingly when iOS attempts to call my app with a BGAppRefreshTask: Thread 23 Queue: com.apple.BGTaskScheduler (com.mycompany.MyApp.RefreshTask) (serial) 0 _dispatch_assert_queue_fail 12 _pthread_wqthread Enqueued from com.apple.duet.activityscheduler.client.xpcqueue (Thread 23) 0 dispatch_async 20 start_wqthread I can't quite understand the reason from this crash. In the background task, I'm attempting to update live activities. In the process, it might encounter code that calls MainActor and manipulate @Observable objects. Might that be the reason?
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471
Feb ’25
How to detect or opt out of iOS app prewarming?
Hi, We are running into issues with iOS app prewarming, where the system launches our app before the user has entered their passcode. In our case, the app stores flags, counters, and session data in UserDefaults and the Keychain. During prewarm launches: UserDefaults only returns default values (nil, 0, false). We have no way of knowing whether this information is valid or just a placeholder caused by prewarming. Keychain items with kSecAttrAccessibleAfterFirstUnlockThisDeviceOnly are inaccessible, which can lead to broken business logic (the app can assume no session exists). No special launch options or environment variables appear to be set. We can reproduce this 100% of the time by starting a Live Activity in the app before reboot. Here’s an example of the workaround we tried, following older recommendations: __attribute__((constructor)) static void ModuleInitializer(void) { char* isPrewarm = getenv("ActivePrewarm"); if (isPrewarm != NULL && isPrewarm[0] == '1') { exit(0); // prevent prewarm launch from proceeding } } On iOS 16+, the ActivePrewarm environment variable doesn’t seem to exist anymore (though older docs and SDKs such as Sentry reference it). We also tried listening for UIApplication.protectedDataDidBecomeAvailableNotification, but this is not specific to prewarming (it also fires when the device gets unlocked) and can cause watchdog termination if we delay work too long. Questions: Is there a supported way to opt out of app prewarming? What is the correct way to detect when an app is being prewarmed? Is the ActivePrewarm environment variable still supported in iOS 16+? Ideally, the UserDefaults API itself should indicate whether it is returning valid stored values or defaults due to the app being launched in a prewarm session. We understand opting out may impact performance, but data security and integrity are our priority. Any guidance would be greatly appreciated.
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178
Oct ’25
SSO Extension Fails XPC Connection to System Daemon (mach-lookup exception used)
Hello, I'm running into an issue with a complex macOS application (non-AppStore) structure involving an unsandboxed system daemon and a sandboxed SSO Extension attempting to communicate via XPC Mach service. The macOS app is composed of three main components: Main App: unsandboxed, standard macOS application. System Daemon: unsandboxed executable installed with a .plist to /Library/LaunchDaemons/ and loaded by launchd. It exposes an XPC Mach Service. SSO Extension: a sandboxed Authentication Services Extension (ASAuthorizationProviderExtension). Main App to System Daemon communication works perfectly. The unsandboxed main app can successfully create and use an XPC connection to the System Daemon's Mach service. But SSO Extension cannot establish an XPC connection to the System Daemon's Mach service, despite using the recommended temporary exception entitlement. I have added the following entitlement to the SSO Extension's entitlements file: <key>com.apple.security.temporary-exception.mach-lookup.global-name</key> <array> <string>my.xpc.service.system.daemon</string> </array> (The name my.xpc.service.system.daemon is the exact name registered by the System Daemon in its Launch Daemon plist's MachServices dictionary.) When the SSO Extension attempts to create the connection, the following log output is generated: default 08:11:58.531567-0700 SSOExtension [0x13f19b090] activating connection: mach=true listener=false peer=false name=my.xpc.service.system.daemon default 08:11:58.532150-0700 smd [0xb100d8140] activating connection: mach=false listener=false peer=true name=com.apple.xpc.smd.peer[1575].0xb100d8140 error 08:11:58.532613-0700 smd Item real path failed. Maybe the item has been deleted? error 08:11:58.532711-0700 SSOExtension Unable to find service status () error: 22 The error Unable to find service status () error: 22. Error code 22 typically translates to EINVAL (Invalid argument), but in this context, it seems related to the system's ability to find and activate the service for the sandboxed process. Questions: Is the com.apple.security.temporary-exception.mach-lookup.global-name entitlement sufficient for a sandboxed SSO Extension to look up a system-wide Launch Daemon Mach service, or are there additional restrictions or required entitlements for extensions? The smd log output Item real path failed. Maybe the item has been deleted? seems concerning. Since the unsandboxed main app can connect, this suggests the service is running and registered. Could this error indicate a sandbox permission issue preventing smd from verifying the path for the sandboxed process? Are there specific sandboxing requirements for Mach service names when communicating from an Extension versus a main application? Any guidance on how a sandboxed SSO Extension can reliably connect to an unsandboxed, non-app-group-related system daemon via XPC Mach service would be greatly appreciated!
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134
Oct ’25
Recursively walk a directory using File Coordination
What’s the recommended way to recursively walk through a directory tree using File Coordination? From what I understand, coordinating a read of a directory only performs a “shallow” lock; this would mean that I’d need to implement the recursive walk myself rather than use FileManager.enumerator(at:includingPropertiesForKeys:options:errorHandler:) plus a single NSFileCoordinator.coordinate(with:queue:byAccessor:) call. I’m trying to extract information from all files of a particular type, so I think using NSFileCoordinator.ReadingOptions.immediatelyAvailableMetadataOnly on each file before acquiring a full read lock on it (if it’s the right file type) would make sense. Am I on the right track?
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136
Oct ’25
What is the new name of the OSDUIHelper process on macOS Tahoe?
I am currently developing a macOS app that can show system HUDs in the Notch Till Sequoia I used to kill the OSDUIHelper process (which displays the default macOS Volume and Brightness control HUDs) - and replaced it with my app's HUDs But, it is not working on macOS Tahoe anymore as the OSDUIHelper process is no longer there due to the UI changes Has the process been renamed - or is there any other way to kill the process?
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119
Oct ’25
Bluetooth work with BGTaskScheduler
Hi All, I'm working on an app that needs to connect to BLE device and on defined schedules download data from the device. the amount of data is segnificant and might take around a minute to download. we tought about utilizing both state restoration and preservation for app waking and scheduling (triggered by the ble peripheral) and BGTaskScheduler to schedule a task that will handle a long running task to manage the full data download. now, will this solution in general valid? isnt it a "hack" that goes around the 10s limit that state restoration enforces? i know there are limitations for BGTask (like when it runs, it might be terminated by the system etc) but considering that, can we proceed with this approach without breaching apple guidelines? thank you in advance!
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177
Oct ’25
Does Mac Catalyst support Background Processing?
I have an app for macOS that is built using Mac Catalyst. I need to perform some background processing. I'm using BGProcessingTaskRequest to schedule the request. I have also integrated CKSyncEngine so I need that to be able to perform its normal background processing. On iOS, when the user leaves the app, I can see a log message that the request was scheduled and a bit later I see log messages coming from the actual background task code. On macOS I ran the app from Xcode. I then quit the app (Cmd-q). I can see the log message that the request was scheduled. But the actual task is never run. In my test, I ran my app on a MacBook Pro running macOS 26.0. When I quit the app, I checked the log file in the app sandbox and saw the message that the task was scheduled. About 20 minutes later I closed the lid on the MacBook Pro for the night. I did not power down, it just went to sleep. Roughly 10 hours later I opened the lid on the MacBook Pro, logged in, and checked the log file. It had not been updated since quitting the app. I should also mention that the laptop was not plugged in at all during this period. My question is, does a Mac Catalyst app support background processing after the user quits the app? If so, how is it enabled? The documentation for BGProcessingTaskRequest and BGProcessingTask show they are supported under Mac Catalyst, but I couldn't find any documentation in the Background Tasks section that mentioned anything specific to setup for Mac Catalyst. Running the Settings app and going to General -> Login Items & Extension, I do not see my app under the App Background Activity section. Does it need to be listed there? If so, what steps are needed to get it there? If this is all documented somewhere, I'd appreciate a link since I was not able to find anything specific to making this work under Mac Catalyst.
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156
Nov ’25