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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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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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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Jan ’26
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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Jan ’26
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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Jan ’26
Misusing a Mutex
This is a successor to: https://developer.apple.com/forums/thread/814231 I went into a slightly different direction. I generated more AI slop that use NSLock. Then I had the NSLock usage changed to Mutex usage. Now it crashes with: Task 13: EXC_BREAKPOINT (code=1, subcode=0x18d29326c) On one of the mutex closures. With an extended description: warning: TypeSystemSwiftTypeRef::operator(): had to engage SwiftASTContext fallback for type $s7Combine10PublishersO21LineBreakingPublisherE11SplitAtZeroV12Subscription33_D18F5AAE73662968F407B0A79FBD1F8DLLCy_x_qd__GD I put the class, a Subscription nested in its corresponding Publisher operator, in the given file Subscription.txt
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Unable to set subtitle when BGContinuedProcessingTask expires
Hi, I've now identified a few areas when BGContinuedProcessingTask gets expired by the system no progress for ~30 seconds high CPU usage high temperature Some of these I can preempt and expire preemptively and handle the notification, others I cannot and just need to let the failure bubble up. When the failure does bubble up, I'd like to update the title and subtitle. I'm able to update the title, but the subtitle is fixed at "Task Failed" Is there any workaround? Or shall I file a bug here?
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Unix Domain Socket path for IPC between LaunchDaemon and LaunchAgent
Hello, I am working on a cross-platform application where IPC between a LaunchDaemon and a LaunchAgent is implemented via Unix domain sockets. On macOS, the socket path length is restricted to 104 characters. What is the Apple-recommended directory for these sockets to ensure the path remains under the limit while allowing a non-sandboxed agent to communicate with a root daemon? Standard paths like $TMPDIR are often too long for this purpose. Thank you in advance!
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