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 or processing app
I am writing an app which mainly is used to update data used by other apps on the device. After the user initializes some values in the app, they almost never have to return to it (occasionally to add a "friend"). The app needs to run a background task at least daily, however, without the user's intervention (or even awareness, once they've given permission). My understanding of background refresh tasks is that if the user doesn't activate the app in the foreground periodically, the scheduled background tasks may never run. If this is true, do I want to use a background processing task instead, or is there a better solution (or have I misunderstood entirely)?
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412
Jan ’25
Why is xpc_connection_set_peer_code_signing_requirement() closing the connection instead of returning XPC_ERROR_PEER_CODE_SIGNING_REQUIREMENT?
I'm using libxpc in a C server and Swift client. I set up a code-signing requirement in the server using xpc_connection_set_peer_code_signing_requirement(). However, when the client doesn't meet the requirement, the server just closes the connection, and I get XPC_ERROR_CONNECTION_INTERRUPTED on the client side instead of XPC_ERROR_PEER_CODE_SIGNING_REQUIREMENT, making debugging harder. What I want: To receive XPC_ERROR_PEER_CODE_SIGNING_REQUIREMENT on the client when code-signing fails, for better debugging. What I’ve tried: Using xpc_connection_set_peer_code_signing_requirement(), but it causes the connection to be dropped immediately. Questions: Why does the server close the connection without sending the expected error? How can I receive the correct error on the client side? Are there any other methods for debugging code-signing failures with libxpc? Thanks for any insights!
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482
Feb ’25
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
SMAppService daemon not running
My app uses SMAppService to register a privileged helper, the helper registers without errors, and can be seen in System Settings. I can get a connection to the service and a remote object proxy, but the helper process cannot be found in Activity Monitor and the calls to the proxy functions seem to always fail without showing any specific errors. What could be causing this situation?
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250
Jul ’25
Does BGAppRefreshTask require an internet connection?
Basically the title. I am trying to implement a local notification to trigger, regardless of internet connection, around 3-5pm if a certain array in the app is not empty to get the user to sync unsaved work with the cloud. I wanted to used the BGAppRefreshTask as I saw it was lightweight and quick for just posting a banner notification but after inspecting it in the console, it looks like it needs internet connection to trigger. Is this the case or am I doing something wrong? Should I be using the BGProcessingTask instead?
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95
Jul ’25
Issue with launchd Job Not Running – "Bootstrap failed: 5: Input/output error"
Purpose I want to use launchd to run a shell script asynchronously every minute, but I'm encountering an issue where the job does not run, and I receive the error "Bootstrap failed: 5: Input/output error". I need help identifying the cause of this issue and how to configure launchd correctly. What I've done Created the shell script (test_ls_save.sh) The script is designed to list the contents of the desktop and save the output to a specified directory. #!/bin/bash DATE=$(date +%Y-%m-%d_%H-%M-%S) SAVE_DIR=/Users/test/Desktop/personal/log_gather FILE_NAME="ls_output_$DATE.log" ls ~/Desktop > "$SAVE_DIR/$FILE_NAME" echo "ls output saved to $SAVE_DIR/$FILE_NAME" File permissions (ls -l output): -rwxr-xr-x 1 test staff 1234 Feb 17 10:00 /Users/test/Desktop/personal/log_gather/exec/test_ls_save.sh Created the launchd plist file (com.test.logTest.plist) The plist file is configured to execute the shell script every minute. <key>Label</key> <string>com.test.logTest</string> <key>ProgramArguments</key> <array> <string>/bin/bash</string> <string>-c</string> /Users/test/Desktop/personal/log_gather/exec/test_ls_save.sh </array> <key>StartInterval</key> <integer>60</integer> <!-- Run every minute --> File permissions (ls -l output): -rwxr-xr-x 1 test staff 512 Feb 17 10:00 /Users/test/Library/LaunchAgents/com.test.logTest.plist Ran the job with launchctl I used the following command to load the plist file into launchd: sudo launchctl bootstrap gui/$(id -u) /Users/test/Library/LaunchAgents/com.test.logTest.plist pc spec MacBook Pro Apple M1 16 GB RAM macOS 15.3 (Build 24D60) what I know The configuration has been set, but the launchd job is not running every minute as expected. I don't believe there is a mistake with the path. When I check the job using launchctl list, the job does not appear in the list. I don't know where the error log files are supposed to be. I checked /var/log/system.log, but there are no error logs. The .sh file runs fine by itself, but it cannot be executed via launchctl. Want to ask What could be the cause of the launchd job not running as expected? Also, is there a way to check where the logs are being output? If there is an error in the plist file configuration, which part should be modified? Specifically, what improvements should be made regarding environment variables and path settings? If my information is not enough, please tell me what is not enough!
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624
Feb ’25
Issue with Developer App Crashing on iPad Upon Launch
Recently, after updating the Developer app to the latest version, my iPad has been unable to open this app as it crashes immediately upon launch. Prior to the update, the app functioned normally. My device is an 11-inch iPad Pro from 2021, running iPadOS 17.3. I have tried troubleshooting steps such as reinstalling the app and restarting the device, but these actions have not resolved the issue. However, I need to use this specific version of the system, iPadOS 17.3, for software testing purposes and cannot upgrade the system. Other apps on my device work normally without any issues. Is there a solution to this problem? I have attempted to contact the developer support team in China, but they were also unable to provide a resolution. This issue is reproducible 100% of the time on my iPad.
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376
Jan ’25
HELP: Privileged Helper With SMAppService
Hi! I've been developing iOS and macOS apps for many years, but now I am looking to dive into smth i have never touched before, namely privileged helpers, and i am struggling hard trying to find my footing. Here’s my use case: I have a CLI tool that requires elevated privileges. I want to create a menu bar app that can interact with this tool, but I’m struggling to find solid documentation or examples of how to accomplish this using SMAppService. I might just be missing something obvious. If anyone could point me toward relevant documentation, examples, articles, tutorials, or even a WWDC session that covers running privileged helpers with SMAppService, I would greatly appreciate it. Thanks in advance!
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487
Feb ’25
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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184
Oct ’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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147
Jul ’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
Some questions about how to use the Background Assets capability on iOS
Regarding the Background Assets capability on iOS: In the install scenario, resources defined as the "install" type are incorporated into the App Store download progress. Do resources of the "update" type in the update scenario also get incorporated into the App Store download progress in the same way? If an exception occurs during the download of install-type resources and the download cannot proceed further, will the system no longer actively block users from launching the app and instead enable the launch button? Currently, if a user has enabled automatic updates on their device, after the app is updated and released on the App Store, will the Background Assets download start immediately once the automatic update completes? Or does Background Assets have its own built-in scheduling logic that prevents it from running concurrently with the automatic update?
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4w
APP Background Keep-Alive
Dear Apple: We are developing an app for file sharing between mobile devices. We want to create an iOS app that can continue sharing files with other devices even when it is running in the background. We are using WLAN channels for file sharing. Could you please advise on which background persistence measures we should use to ensure the iOS app can maintain file transfer when it goes to the background? Thank you.
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122
Apr ’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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75
Nov ’25
Effect of App Nap on 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?
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122
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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94
May ’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
Spawning electron app from deamon process
Hi all, Our company has an application that runs on several machines, this app is launched via a deamon that keeps it alive. One of the feature of this app, is to start a headless electron application to run some tests. When spawning this electron application with the new arm64 OS, we are getting this issue: Silent Test Agent Worker exited with code: 133 [ERROR] [75873:0205/135842.347044:ERROR:mach_port_rendezvous.cc(384)] bootstrap_look_up com.hivestreaming.silenttestagent.MachPortRendezvousServer.1: Permission denied (1100) [ERROR] [75873:0205/135842.347417:ERROR:shared_memory_switch.cc(237)] No rendezvous client, terminating process (parent died?) [ERROR] [75872:0205/135842.347634:ERROR:mach_port_rendezvous.cc(384)] bootstrap_look_up com.hivestreaming.silenttestagent.MachPortRendezvousServer.1: Permission denied (1100) [ERROR] [75872:0205/135842.347976:ERROR:shared_memory_switch.cc(237)] No rendezvous client, terminating process (parent died?) Both application (main app and electron one) are signed and notarized, but it seems that there is some other permission issue. If we run the electron application manually, all runs as expected. I added the crash report as attachment CrashReport.log
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528
Feb ’25