Processes & Concurrency

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Discover how the operating system manages multiple applications and processes simultaneously, ensuring smooth multitasking performance.

Concurrency Documentation

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Background Refresh Stalls After Charging on watchOS 26
Hello everyone, I’m a new developer still learning as I go. I’m building a simple watchOS app that tracks Apple Watch battery consumption, records hourly usage data, and uses that information to predict battery life in hours. I’ve run into an issue where background refresh completely stalls after charging and never recovers, regardless of what I do. The only way to restore normal behavior is to restart the watch. Background refresh can work fine for days, but if the watch is charging and a scheduled background refresh tries to run during that period, it appears to be deferred—and then remains in that deferred state indefinitely. Even reopening the app or scheduling new refreshes doesn’t recover it. Has anyone else encountered this behavior? Is there a reliable workaround? I’ve seen a few reports suggesting that there may be a regression in scheduleBackgroundRefresh() on watchOS 26, where tasks are never delivered after certain states. Any insights or confirmations would be greatly appreciated. Thank you!
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190
Oct ’25
iOS26 background lock screen Blood glucose monitoring Bluetooth low energy disconnect sleep
First, our app communicates with our blood glucose monitor (CGM) using Bluetooth Low Energy (BLE). On an iPhone 14 Pro with iOS 26.0.1, Bluetooth communication works properly even when the app is in the background and locked. Even if the phone and CGM are disconnected, the app continues to scan in the background and reconnects when the phone and CGM are back in close proximity. It won't be dormant in the background or when the screen is locked. This effectively ensures that diabetic users can monitor their blood glucose levels in real time. However, after using iOS 26.0.1 on the iPhone 17, we've received user feedback about frequent disconnections in the background. Our logs indicate that Bluetooth communication is easily disconnected when switching to the background, and then easily dormant by the system, especially when the user's screen is locked. This situation significantly impacts users' blood glucose monitoring, and users are unacceptable. What can be done?
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176
Oct ’25
Can we create a bundled non-interactive macOS application which uses CFRunLoop only(instead of using NSApplicationMain to run NSRunLoop)?
I am developing a macOS non-interactive macOS application which does not show any ui. i want to block main thread and do all the work on worker thread . Once done with work in worker thread, want to unblock main thread by exiting event loop to terminate application. Because i dont want to show any UI or use any Foundation/Cocoa functionality, i am thinking of using CFRunLoop to block main thread from exiting until i finish my work in worker thread. When i tried this in a project, I am able to finish work in worker thread after block main thread using CFRunLoop. I also want this application to be a bundled application, which can be launched by double clicking on application bundle . But when i tried it in my xcode project by launching it using double clicking on application bundle, application keeps on toggling/bouncing in the dock menu with a status "Not responding". Although i am able to complete my work in worker thread. import Foundation let runLoop = CFRunLoopGetCurrent() func workerTask() { DispatchQueue.global().async { print("do its work") sleep(5) // do some work print("calling exit event loop") CFRunLoopStop(runLoop) print ("unblocking main thread") } } workerTask () // blocking main thread print ("blocked main thread") CFRunLoopRun() print ("exit") Why i am getting this application bouncing in doc menu behavior ? I tried by using NSApplicationMain instead of CFRunLoop in my project, in that case i didnt get this behavior . Does NSApplicationMain does some extra work before starting NSRunLoop which i am not doing while using CFRunLoop, which is showing this toggling/Bouncing application icon in Dock menu ? or Is this bouncing app icon issue is related to run loop i am using which is CFRunLoop ? Note : If i dont use a bundled application and use a commandline application then i am able to do all steps in worker thread and exit main thread as i wanted after finishing my work . But i need to do all this in application which can be launched using double clicking (bundled applcation). If not by using CFRunLoop, then how can i achive this ? - Create a application which shows no UI and do all work in worker thread while main thread is blocked. Once work is done unblock main thread and exit. And user should be able to launch application using double click the application icon.
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Mar ’25
Prevent my app from background activity
When I search, it's always people trying to do stuff in the background. I want my app to only do stuff when it is active. And this post https://developer.apple.com/forums/thread/685525 seems to have prevented replies from the start. Which means it's just a documentation page and does not belong in the discussion forums at all, because it prevents all discussion.
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May ’25
BGContinuedProcessingTask UI
When I use BGContinuedProcessingTask to submit a task, my iPhone 12 immediately shows a notification banner displaying the task’s progress. However, on my iPhone 15 Pro Max, there’s no response — the progress UI only appears in the Dynamic Island after I background the app. Why is there a difference in behavior between these two devices? Is it possible to control the UI so that the progress indicator only appears when the app moves to the background?
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238
Oct ’25
SMAppService
Hello, https://developer.apple.com/forums/thread/802443 https://developer.apple.com/documentation/servicemanagement/updating-helper-executables-from-earlier-versions-of-macos https://developer.apple.com/documentation/ServiceManagement/updating-your-app-package-installer-to-use-the-new-service-management-api#Run-the-sample-launch-agent Read these. Earlier we had a setup with SMJobBless, now we have migrated to SMAppService. Everything is working fine, the new API seems easier to manage, but we are having issues with updating the daemon. I was wondering, what is the right process for updating a daemon from app side? What we are doing so far: App asks daemon for version If version is lower than expected: daemon.unregister(), wait a second and daemon.register() again. The why? We have noticed that unregistering/registering multiple times, of same daemon, can cause the daemon to stop working as expected. The daemon toggle in Mac Settings -> Login Items & Extensions can be on or off, but the app can still pickup daemon running, but no daemon running in Activity monitor. Registration/unregistration can start failing and nothing helps to resolve this, only reseting with sfltool resetbtm and a restart seems to does the job. This is usually noticeable for test users, testing same daemon version with different app builds. In production app, we also increase the bundle version of daemon in plist, in test apps we - don't. I haven't found any sources of how the update of pre-bundled app daemon should work. Initial idea is register/unregister, but from what I have observed, this seems to mess up after multiple registrations. I have a theory, that sending the daemon a command to kill itself after app update, would load the latest daemon. Also, I haven't observed for daemon, with different build versions to update automatically. What is the right way to update a daemon with SMAppService setup? Thank you in advance.
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Nov ’25
BGContinuedProcessingTask what's the point?
Hi, This post is coming from frustration of working on using BGContinuedProcessingTask for almost 2 weeks, trying to get it to actually complete in the background after the app is backgrounded. My process will randomlly finish and not finish and have no idea why. I'm properly using and setting task?.progress.totalUnitCount = [some number] task?.progress.completedUnitCount = [increment as processed] I know this, because it all looks propler as long as the app insn't backgrounded. So it's not a progress issue. The task will ALWAYS complete. The device has full power, as it is plugged in as I run from within Xcode. So, it's not a power issue. Yes, the process will take a few minutes, but I thought that is BGContinuedProcessingTask purpose in iOS 26. For long running process that a user could place in the background and leave the app, assuming the process would actually finish. Why bother introducing a feature that only works with short tasks that don't actually need long running time in the first place.
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Oct ’25
TCC Permission Inheritance Failure: Swift Parent -> Python Child
TCC Permission Inheritance for Python Process Launched by Swift App in Enterprise Deployment We are developing an enterprise monitoring application that requires a hybrid Swift + Python architecture due to strict JAMF deployment restrictions. We must deploy a macOS application via ABM/App Store Connect, but our core monitoring logic is in a Python daemon. We need to understand the feasibility and best practices for TCC permission inheritance in this specific setup. Architecture Component Bundle ID Role Deployment Swift Launcher com.athena.AthenaSentry Requests TCC permissions, launches Python child process. Deployed via ABM/ASC. Python Daemon com.athena.AthenaSentry.Helper Core monitoring logic using sensitive APIs. Nested in Contents/Helpers/. Both bundles are signed with the same Developer ID and share the same Team ID. Required Permissions The Python daemon needs to access the following sensitive TCC-controlled services: Screen Recording (kTCCServiceScreenCapture) - for capturing screenshots. Input Monitoring (kTCCServiceListenEvent) - for keystroke/mouse monitoring. Accessibility (kTCCServiceAccessibility) - a prerequisite for Input Monitoring. Attempts & Workarounds We have attempted to resolve this using: Entitlement Inheritance: Added com.apple.security.inherit to the Helper's entitlements. Permission Proxy: Swift app maintains active event taps to try and "hold" the permissions for the child. Foreground Flow: Keeping the Swift app in the foreground during permission requests. Questions Is this architecture supported? Can a Swift parent app successfully request TCC permissions that a child process can then use? TCC Inheritance: What are the specific rules for TCC permission inheritance between parent/child processes in enterprise environment? What's the correct approach for this enterprise use case? Should we: Switch to a Single Swift App? (i.e., abandon the Python daemon and rewrite the core logic natively in Swift). Use XPC Services? (instead of launching the child process directly).
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Nov ’25
BGContinuedProcessingTask expiring unpredictably
I've adopted the new BGContinuedProcessingTask in iOS 26, and it has mostly been working well in internal testing. However, in production I'm getting reports of the tasks failing when the app is put into the background. A bit of info on what I'm doing: I need to download a large amount of data (around 250 files) and process these files as they come down. The size of the files can vary: for some tasks each file might be around 10MB. For other tasks, the files might be 40MB. The processing is relatively lightweight, but the volume of data means the task can potentially take over an hour on slower internet connections (up to 10GB of data). I set the totalUnitCount based on the number of files to be downloaded, and I increment completedUnitCount each time a file is completed. After some experimentation, I've found that smaller tasks (e.g. 3GB, 10MB per file) seem to be okay, but larger tasks (e.g. 10GB, 40MB per file) seem to fail, usually just a few seconds after the task is backgrounded (and without even opening any other apps). I think I've even observed a case where the task expired while the app was foregrounded! I'm trying to understand what the rules are with BGContinuedProcessingTask and I can see at least four possibilities that might be relevant: Is it necessary to provide progress updates at some minimum rate? For my larger tasks, where each file is ~40MB, there might be 20 or 30 seconds between progress updates. Does this make it more likely that the task will be expired? For larger tasks, the total time to complete can be 60–90 mins on slower internet connections. Is there some maximum amount of time the task can run for? Does the system attempt some kind of estimate of the overall time to complete and expire the task on that basis? The processing on each file is relatively lightweight, so most of the time the async stream is awaiting the next file to come down. Does the OS monitor the intensity of workload and suspend the task if it appears to be idle? I've noticed that the task UI sometimes displays a message, something along the lines of "Do you want to continue this task?" with a "Continue" and "Stop" option. What happens if the user simply ignores or doesn't see this message? Even if I tap "Continue" the task still seems to fail sometimes. I've read the docs and watched the WWDC video, but there's not a whole lot of information on the specific issues I mention above. It would be great to get some clarity on this, and I'd also appreciate any advice on alternative ways I could approach my specific use case.
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Dec ’25
How to Handle Asynchronous Operations in BGContinuedProcessingTask
I would like to know whether BGContinuedProcessingTaskRequest supports executing asynchronous tasks internally, or if it can only execute synchronous tasks within BGContinuedProcessingTaskRequest? Our project is very complex, and we now need to use BGContinuedProcessingTaskRequest to perform some long-running operations when the app enters the background (such as video encoding/decoding & export). However, our export interface is an asynchronous function, for example video.export(callback: FinishCallback). This export call returns immediately, and when the export completes internally, it calls back through the passed-in callback. So when I call BGTaskScheduler.shared.register to register a BGContinuedProcessingTask, what should be the correct approach? Should I directly call video.export(nil) without any waiting, or should I wait for the export function to complete in the callback? For example: BGTaskScheduler.shared.register(forTaskWithIdentifier: "com.xxx.xxx.xxx.xxx", using: nil) { task in guard let continuedTask = task as? BGContinuedProcessingTask else { task.setTaskCompleted(success: false) return } let scanner = SmartAssetsManager.shared let semaphore = DispatchSemaphore(value: 0) continuedTask.expirationHandler = { logError(items: "xwxdebug finished.") semaphore.signal() } logInfo(items: "xwxdebug start!") video.export { _ in semaphore.signal() } semaphore.wait() logError(items: "xwxdebug finished!") }
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Nov ’25
Background Task Execution for FDA Class B Medical App Using BLE
Hello Apple Developer Community, I am developing a medical app that is classified as Class B according to FDA regulations. The app connects to a medical device using Bluetooth Low Energy (BLE) to collect critical medical data such as ECG readings. To ensure accurate data collection and maintain the quality of the medical readings, the app needs to wake up every five minutes in the background and perform tasks for approximately 30 seconds. I understand that iOS has strict limitations on background execution to preserve battery and system performance. However, due to the medical nature of the app and the need for periodic data collection, I am seeking guidance on the following: If I can provide documentation that the app is associated with an FDA-approved Class B medical device, would Apple allow more lenient background task execution policies? Are there specific APIs, such as BackgroundTasks, CoreBluetooth, or other recommended strategies, that could help me achieve this behavior reliably? Is there a process to apply for an exception or special consideration for medical apps that require periodic background activity? Any insights or recommendations would be greatly appreciated. Thank you!
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Mar ’25
NSXPCListener only working while Debugging `listener failed to activate: xpc_error=[1: Operation not permitted]`
I am building a Mac app that launch a GUI helper app and use XPC to communicate between them. Main app start a XPC Listener using NSXPCListener(machServiceName: "group.com.mycompany.myapp.xpc") Launch the helper app Helper app connect to the XPC service and listen command from main app. What I observe is the app seems can start XPC listener while I run it via Xcode. If I run the app using TestFlight build, or via the compiled debug binary (same one that I use on Xcode), it cannot start the XPC service. Here is what I see in the Console: [0x600000ef7570] activating connection: mach=true listener=true peer=false name=group.com.mycompany.myapp.xpc [0x600000ef7570] listener failed to activate: xpc_error=[1: Operation not permitted] Both main app and helper app are sandboxed and in the same App Group - if they were not, I cannot connect the helper app to main app. I can confirm the entitlement profiles did contain the app group. If I start the main app via xcode, and then launch the helper app manually via Finder, the helper app can connect to the XPC and everything work. It is not related to Release configuration, as the same binary work while I am debugging, but not when I open the binary manually. For context, the main app is a Catalyst app, and helper app is an AppKit app. To start a XPC listener on Catalyst, I had do it in a AppKit bridge via bundle. Given the app worked on Xcode, I believe this approach can work. I just cannot figure out why it only work while I am debugging. Any pointer to debug this issue is greatly appreciated. Thanks!
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125
May ’25
What happens after BGContinuedProcessingTask "expires"?
If I create a BGContinuedProcessingTaskRequest, register it, and then "do work" within it appropriately reporting progress, and before my task has finished doing all the work it had to do, its expirationHandler triggers... does the task later try again? Or does it lose the execution opportunity until the app is next re-launched to the foreground? In my testing, I never saw my task execute again once expired (which suggests the latter?). I was able to easily force this expiry by starting my task, backgrounding my app, then launching the iOS Camera App. My example is just using test code inspired from https://developer.apple.com/documentation/backgroundtasks/performing-long-running-tasks-on-ios-and-ipados let request = BGContinuedProcessingTaskRequest(identifier: taskIdentifier, title: "Video Upload", subtitle: "Starting Upload") request.strategy = .queue BGTaskScheduler.shared.register(forTaskWithIdentifier: taskIdentifier, using: nil) { task in guard let task = task as? BGContinuedProcessingTask else { return } print("i am a good task") var wasExpired = false task.expirationHandler = { wasExpired = true } let progress = task.progress progress.totalUnitCount = 100 while !progress.isFinished && !wasExpired { progress.completedUnitCount += 1 let formattedProgress = String(format: "%.2f", progress.fractionCompleted * 100) task.updateTitle(task.title, subtitle: "Completed \(formattedProgress)%") sleep(1) } if progress.isFinished { print ("i was a good task") task.setTaskCompleted(success: true) } else { print("i was not a good task") task.setTaskCompleted(success: false) } } try? BGTaskScheduler.shared.submit(request) Apologies if this is clearly stated somewhere and I'm missing it.
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85
Nov ’25
Push-to-Start Live Activity Background Task Issue After App Termination
Desired Behavior I want the app to be able to handle multiple Push-to-Start notifications even when it is completely terminated. Each Live Activity should: Be successfully displayed upon receiving a Push-to-Start notification. Trigger background tasks to send its update token to the server, regardless of the time interval between notifications. Problem I am facing an issue with iOS Live Activities when using Push-to-Start notifications to trigger Live Activities in an app that has been completely terminated. Here’s the detailed scenario: When the app is completely terminated and I send the first Push-to-Start notification: The Live Activity is successfully displayed. didFinishLaunchingWithOptions` is triggered, and background tasks execute correctly, including sending the update token to the server. When I send consecutive Push-to-Start notifications in quick succession (e.g., within a few seconds or minutes): Both notifications successfully display their respective Live Activities. Background tasks are executed correctly for both notifications. However, when there is a longer interval (e.g., 10 minutes) between two Push-to-Start notifications: The first notification works perfectly—it displays the Live Activity, triggers didFinishLaunchingWithOptions, and executes background tasks. The second notification successfully displays the Live Activity but fails to execute any background tasks, such as sending the update token to the server. My HypothesisI suspect that iOS might impose a restriction where background runtime for Push-to-Start notifications can only be granted once within a certain time frame after the app has been terminated. Any insights into why this issue might be occurring or how to ensure consistent background task execution for multiple Push-to-Start notifications would be greatly appreciated!
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424
Mar ’25
BGContinuedProcessingTask register block not called, submit does not throw an error
I implemented BGContinuedProcessingTask in my app and it seems to be working well for everyone except one user (so far) who has reached out to report nothing happens when they tap the Start Processing button. They have an iPhone 12 Pro Max running iOS 26.1. Restarting iPhone does not fix it. When they turn off the background processing feature in the app, it works. In that case my code directly calls the function to start processing instead of waiting for it to be invoked in the register block (or submit catch block). Is this a bug that's possible to occur, maybe device specific? Or have I done something wrong in the implementation? func startProcessingTapped(_ sender: UIButton) { if isBackgroundProcessingEnabled { startBackgroundContinuedProcessing() } else { startProcessing(backgroundTask: nil) } } func startBackgroundContinuedProcessing() { BGTaskScheduler.shared.register(forTaskWithIdentifier: taskIdentifier, using: .main) { @Sendable [weak self] task in guard self != nil else { return } startProcessing(backgroundTask: task as? BGContinuedProcessingTask) } let request = BGContinuedProcessingTaskRequest(identifier: taskIdentifier, title: title, subtitle: subtitle) request.strategy = .fail if BGTaskScheduler.supportedResources.contains(.gpu) { request.requiredResources = .gpu } do { try BGTaskScheduler.shared.submit(request) } catch { startProcessing(backgroundTask: nil) } } func startProcessing(backgroundTask: BGContinuedProcessingTask?) { // FIXME: Never called for this user when isBackgroundProcessingEnabled is true }
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3w
How to check for cancellation of background task
When using the old withTaskCancellationHandler(operation:onCancel:isolation:) to run background tasks, you were notified that the background task gets cancelled via the handler being called. SwiftUI provides the backgroundTask(_:action:) modifier which looks quite handy. However how can I check if the background task will be cancelled to avoid being terminated by the system? I have tried to check that via Task.isCancelled but this always returns false no matter what. Is this not possible when using the modifier in which case I should file a bug report? Thanks for your help
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Mar ’25
Background Tasks Resources
General: Forums subtopic: App & System Services > Processes & Concurrency Forums tag: Background Tasks Background Tasks framework documentation UIApplication background tasks documentation ProcessInfo expiring activity documentation Using background tasks documentation for watchOS Performing long-running tasks on iOS and iPadOS documentation WWDC 2020 Session 10063 Background execution demystified — This is critical resource. Watch it! [1] WWDC 2022 Session 10142 Efficiency awaits: Background tasks in SwiftUI WWDC 2025 Session 227 Finish tasks in the background — This contains an excellent summary of the expected use cases for each of the background task types. iOS Background Execution Limits forums post UIApplication Background Task Notes forums post Testing and Debugging Code Running in the Background forums post Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" [1] Sadly the video is currently not available from Apple. I’ve left the link in place just in case it comes back.
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4.0k
Nov ’25
XPC Resources
XPC is the preferred inter-process communication (IPC) mechanism on Apple platforms. XPC has three APIs: The high-level NSXPCConnection API, for Objective-C and Swift The low-level Swift API, introduced with macOS 14 The low-level C API, which, while callable from all languages, works best with C-based languages General: Forums subtopic: App & System Services > Processes & Concurrency Forums tag: XPC Creating XPC services documentation NSXPCConnection class documentation Low-level API documentation XPC has extensive man pages — For the low-level API, start with the xpc man page; this is the original source for the XPC C API documentation and still contains titbits that you can’t find elsewhere. Also read the xpcservice.plist man page, which documents the property list format used by XPC services. Daemons and Services Programming Guide archived documentation WWDC 2012 Session 241 Cocoa Interprocess Communication with XPC — This is no longer available from the Apple Developer website )-: Technote 2083 Daemons and Agents — It hasn’t been updated in… well… decades, but it’s still remarkably relevant. TN3113 Testing and Debugging XPC Code With an Anonymous Listener XPC and App-to-App Communication forums post Validating Signature Of XPC Process forums post This forums post summarises the options for bidirectional communication This forums post explains the meaning of privileged flag Related tags include: Inter-process communication, for other IPC mechanisms Service Management, for installing and uninstalling Service Management login items, launchd agents, and launchd daemons Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com"
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3.2k
Nov ’25