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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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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Oct ’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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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
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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Nov ’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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Dec ’25
LaunchAgent (Mac) as peripheral doesn't show a pairing request.
The same code built in a regular Mac app (with UI) does get paired. The characteristic properties are [.read, .write, .notify, .notifyEncryptionRequired] The characteristic permissions are [.readEncryptionRequired, .writeEncryptionRequired] My service is primary. In the iOS app (central) I try to read the characteristic, but an error is reported: Error code: 5, Description: Authentication is insufficient.
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Dec ’25
MacOS 26 TestFlight SIGKILLs app when updating
We're developing an Electron app for MacOS App Store. When updating our app through TestFlight, TestFlight prompts "Close This App to Update", and when I click "Continue" our app would be "Terminated" for update. Now this is where things go wrong. On MacOS 15 our app seems to be gracefully terminating (We attached it with lldb and it shows that our app returns with 0 when we click "Continue") which is fine. However for MacOS 26 though, it seems that TestFlight just directly SIGKILLs our app (indicated by lldb), which means that all of our app's child processes are left orphaned. Even worse, our app is singleton, which means that when the app relaunches it fails, because the leftover child processes from the previously SIGKILLed session is still alive, and even if we want to kill those orphaned child processes we can't because our app is sandboxed thus cannot kill processes outside of the current sandbox. We captured output from log stream (app name redacted): 12-02 22:08:16.477036-0800 0x5452     Default     0x5a4a7              677    7    installcoordinationd: [com.apple.installcoordination:daemon] -[IXSCoordinatorProgress setTotalUnitsCompleted:]: Progress for coordinator: [com.our.app/Invalid/[user-defined//Applications/OurApp.app]], Phase: IXCoordinatorProgressPhaseLoading, Percentage: 99.454 123: Attempt to set units completed on finished progress: 214095161 2025-12-02 22:08:16.483056-0800 0x53ba     Default     0x5a5c9              167    0    runningboardd: (RunningBoard) [com.apple.runningboard:connection] Received termination request from [osservice<com.apple.installcoordinationd(274)>:677] on <RBSProcessPredicate <RBSProcessBundleIdentifierPredicate "com.our.app">> with context <RBSTerminateContext| explanation:installcoordinationd app:[com.our.app/Invalid/[user-defined//Applications/OurApp.app]] uuid:A3BC0629-124E-4165-ABB7-1324380FC354 isPlaceholder:N re portType:None maxTerminationResistance:Absolute attrs:[ 2025-12-02 22:08:16.488651-0800 0x53ba     Default     0x5a5c9              167    7    runningboardd: (RunningBoard) [com.apple.runningboard:ttl] Acquiring assertion targeting system from originator [osservice<com.apple.installcoordinationd(274)>:677] with description <RBSAssertionDescriptor| "installcoordinationd app:[com.our.app/Invalid/[user-defined//Applications/OurApp.app]] uuid:A3BC0629-124E-4165-ABB7-1324380FC354 isPlaceholder:N" ID:167-677-1463 target:system attributes:[ 2025-12-02 22:08:16.489353-0800 0x53ba     Default     0x5a5c9              167    0    runningboardd: (RunningBoard) [com.apple.runningboard:process] [app<application.com.our.app.485547.485561(501)>:2470] Terminating with context: <RBSTerminateContext| explanation:installcoordinationd app:[com.our.app/Invalid/[user-defined//Applications/OurApp.app]] uuid:A3BC0629-124E-4165-ABB7-1324380FC354 isPlaceholder:N reportType:None maxTerminationResistance:Absolute attrs:[ 2025-12-02 22:10:23.920869-0800 0x5a5a     Default     0x5a4c6              674    14   appstoreagent: [com.apple.appstored:Library] [A95D57D7] Completed with 1 result: <ASDApp: 0xc932a8780>: {bundleID = com.our.app; completedUnitCount = 600; path = /Applications/OurApp.app; installed = 0} 2025-12-02 22:10:32.027304-0800 0x5ae5     Default     0x5a4c7              674    14   appstoreagent: [com.apple.appstored:Library] [BEB5F2FD] Completed with 1 result: <ASDApp: 0xc932a8780>: {bundleID = com.our.app; completedUnitCount = 600; path = /Applications/OurApp.app; installed = 0} 2025-12-02 22:10:36.542321-0800 0x5b81     Default     0x5a4c8              674    14   appstoreagent: [com.apple.appstored:Library] [185B9DD6] Completed with 1 result: <ASDApp: 0xc932a8780>: {bundleID = com.our.app; completedUnitCount = 600; path = /Applications/OurApp.app; installed = 0} The line "Terminating with context" seems suspicious. This line is not seen on MacOS 15, only MacOS 26. Is this documented behavior? If so, how can we handle this?
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Running processing task for data upload together with state restoration
Hi All, In continuation of this thread https://developer.apple.com/forums/thread/804439 I want to perform data upload after getting it from the BLE device. As state restoration wake should not deal with data upload i though of using a processing task to perform the data upload. So the flow will be something like: Connect to device -> listen to notification -> go to background -> wake from notification -> handle data download from ble device -> register processing task for data upload -> hopefully get the data uploaded From reading about processing task i understand that the task execution is completely handled by the OS and depends on user behaviour and app usage. I even saw that if the user is not using the app for a while, the OS might not even perfoirm the task. So my quesiton is: does state restoration wakeup and perfroming data dowloads in the backgound considered app usage that will increase the likeluhood the task will get execution time? Can we rely on this for a scenario that the user opens the app for the first time, register, onboard for ble, connect to devie and then put it in the background for days or weeks and only relying on state restoration and processing tasks to do their thing? Sorry for the long read and appreciate your support! Shimon
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Dec ’25
How do I internally handle conditionally conforming to ConnectablePublisher
I'm making an operator Publisher, which has to wrap the upstream publisher. But I want the operator to conditionally conform to ConnectablePublisher, but only when the upstream publisher does the same. I can make my connect() call the upstream's connect(), but is that all I have to do? That Apple's plumbing will automatically hold back the initial call to the Subscription object if the publisher is connectable. Otherwise, I need to make a flag in the subscription for when to connect, which would involve an infinitely copyable struct somehow send a message to a unique class/actor. That last part makes sense to me, but it also seems like too much work for something plug-and-play. Having Apple's implementation taking care of that issue also makes sense, and would be a better solution.
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BGProcessingTask Not Triggering at Scheduled Time After Updating to Xcode 26.1.1
I’m reaching out regarding an issue we’ve been experiencing with BGProcessingTask since upgrading to Xcode 26.1.1. Issue Summary Our daily background processing task—scheduled shortly after end‑of‑day—has stopped triggering reliably at night. This behavior started occurring only after updating to Xcode 26.1.1. Prior to this update, the task consistently ran around midnight, executed for ~10–15 seconds, and successfully rescheduled itself for the next day. Expected Behavior BGProcessingTask should run at/near the scheduled earliestBeginDate, which we set to roughly 2 hours after end-of-day. The task should execute, complete, and then reschedule itself. Actual Behavior On devices running builds compiled with Xcode 26.1.1, the task does not trigger at all during the night. The same code worked reliably before the Xcode update. No system logs indicate rejection, expiration, or background task denial. Technical Details This is the identifier we use: private enum DayEndProcessorConst {    static let taskIdentifier = "com.company.sdkmanagement.daysummary.manager" } The task is registered as follows: When app launched BGTaskScheduler.shared.register(    forTaskWithIdentifier: DayEndProcessorConst.taskIdentifier,    using: nil ) { [weak self] task in    self?.handleDayEndTask(task) } And scheduled like this: let date = Calendar.current.endOfDay(for: Date()).addingTimeInterval(60 * 60 * 2) let request = BGProcessingTaskRequest(identifier: DayEndProcessorConst.taskIdentifier) request.requiresNetworkConnectivity = true request.requiresExternalPower = false request.earliestBeginDate = date try BGTaskScheduler.shared.submit(request) As per our logs, tasks scheduled successfully The handler wraps the work in an operation queue, begins a UI background task, and marks completion appropriately: task.setTaskCompleted(success: true) Could you please advise whether: There are known issues with BGProcessingTask scheduling or midnight execution in Xcode 26.1.1 or iOS versions associated with it? Any new entitlement, configuration, or scheduler behavior has changed in recent releases? Additional logging or diagnostics can help pinpoint why the scheduler never fires the task?
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