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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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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109
Mar ’25
Is background processing even possible?
Hello, aspiring programmer here. I am developing a StepCounter APP, which keeps track of how many steps I have taken and sends to an MQTT server. I am trying to make this happen even while the app is not in focus, but so far I have not been able to get this working. First tried with silent background music, which seemed pretty inconsistent and inpractical, since I usually play youtube videoes while walking, making the app stop with its silent audio. Then tried GPS, which didnt really do anything (could be implementation problem). Has anyone made background processing work for their apps?
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96
Mar ’25
Need to start the Mac application automatically
I am developing the application in Mac. My requirement is to start the application automatically when user login. I have tried adding the plist file in launch agents, But it doesn't achieve my requirement. Please find the code added in the launch agents <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>Label</key> <string>com.sftk.secure</string> <key>ProgramArguments</key> <array> <string>/Applications/Testing.app/Contents/MacOS/Testing</string> </array> <key>RunAtLoad</key> <true/> <key>KeepAlive</key> <false/> </dict> </plist> I have tried by adding manually in the setting, but it was opened sometimes and closed suddenly. On open manually it works. Please provide a solution to start the application automatically on system starts
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117
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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145
Oct ’25
Running external binaries from Swift Package (TTS engine): Operation not permitted from Xcode app
Hi everyone, We’re developing a macOS SwiftUI app that uses a local Swift Package (CasSherpaCore) to invoke an external compiled binary (sherpa-onnx-offline-tts) for text-to-speech synthesis using system calls. The package works flawlessly when tested from terminal or via a lightweight test C program. However, when we invoke it from a SwiftUI app (even with Full Disk Access granted to Xcode and Terminal), we consistently get the error: sh: /Users/xxxxxxxxxxx/SherpaONNX/sherpa-onnx/build/bin/sherpa-onnx-offline-tts: Operation not permitted We’ve tried: Granting Full Disk Access to Xcode and Terminal. Removing the quarantine flag with xattr -d com.apple.quarantine. Setting executable permission via chmod +x. Using both system() and Process in C and Swift contexts. Testing within a Swift Package that’s integrated into the app as a local dependency. Running the command manually from terminal (works perfectly). It appears that macOS (or Xcode’s runtime sandbox) is restricting execution of binaries from certain locations or contexts when launched via system() inside the app. Questions: Is there a specific entitlement or configuration that allows execution of local binaries from a SwiftUI macOS app? Is this related to System Integrity Protection (SIP) or a hardened runtime limitation? Are there best practices or alternative approaches to safely execute local TTS binaries from within a Swift app? Any help would be deeply appreciated. This is a core feature in our project and we’re stuck at this point. Thank you so much in advance!
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74
Jul ’25
Communicate with running app
I've written an app that uses On Idle (RunHandler) to prompt me to get up and stretch every 30 minutes. Is there anyway to query the running app to determine how long it's been since it last woke up and prompted me? Something like thru the apps properties by right clicking on the icon in the dock?
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319
Dec ’24
SMAppService Error 108 'Unable to read plist' on macOS 15 - Comprehensive Analysis & Test Case
SMAppService Error 108 "Unable to read plist" on macOS 15 Sequoia - Comprehensive Test Case Summary We have a fully notarized SMAppService implementation that consistently fails with Error 108 "Unable to read plist" on macOS 15 Sequoia, despite meeting all documented requirements. After systematic testing including AI-assisted analysis, we've eliminated all common causes and created a comprehensive test case. Error: SMAppServiceErrorDomain Code=108 "Unable to read plist: com.keypath.helperpoc.helper" 📋 Complete Repository: https://github.com/malpern/privileged_helper_help What We've Systematically Verified ✅ Perfect bundle structure: Helper at Contents/MacOS/, plist at Contents/Library/LaunchDaemons/ Correct SMAuthorizedClients: Embedded in helper binary via CREATE_INFOPLIST_SECTION_IN_BINARY=YES Aligned identifiers: Main app, helper, and plist all use consistent naming Production signing: Developer ID certificates with full Apple notarization and stapling BundleProgram paths: Tested both Contents/MacOS/helperpoc-helper and simplified helperpoc-helper Entitlements: Tested with and without com.apple.developer.service-management.managed-by-main-app What Makes This Different Systematic methodology: Not a "help me debug" post - we've done comprehensive testing Expert validation: AI analysis helped eliminate logical hypotheses Reproduction case: Minimal project that demonstrates the issue consistently Complete documentation: All testing steps, configurations, and results documented Use Case Context We're building a keyboard remapper that integrates with https://github.com/jtroo/kanata and needs privileged daemon registration for system-wide keyboard event interception. Key Questions Does anyone have a working SMAppService implementation on macOS 15 Sequoia? Are there undocumented macOS 15 requirements we're missing? Is Error 108 a known issue with specific workarounds? Our hypothesis: This appears to be a macOS 15 system-level issue rather than configuration error, since our implementation meets all documented Apple requirements but fails consistently. Has anyone encountered similar SMAppService issues on macOS 15, or can confirm a working implementation?
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279
Jul ’25
How to safely maximize concurrent UI rendering
I'm using Swift 6 and tasks to concurrently process multiple PDF files for rendering, and it's working well. But currently I'm manually limiting the number of simultaneous tasks to 2 out of fear that the system might run many tasks concurrently without having enough RAM to do the PDF processing. Testing on a variety of devices, I've tried increasing the task limit and haven't seen any crashes, but I'm quite concerned about the possibility. Any given device might be using a lot of RAM at any moment, and any given PDF might strain resources more than the average PDF. Is there a recommended technique for handling this kind of scenario? Should I not worry about it and just go ahead and start a high number of tasks, trusting that the system won't run too many concurrently and therefore won't run out of RAM?
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256
Mar ’25
i can not run "pgrep" or "ps" in sandbox?
Hi. I'm trying to learn macOS app development. i'm trying to run unix commands: func execute(_ command: String) throws -> String { let process = Process() let pipe = Pipe() process.executableURL = URL(fileURLWithPath: "/bin/bash") process.arguments = ["-c", command] process.standardOutput = pipe // process.standardError try process.run() process.waitUntilExit() guard let data = try pipe.fileHandleForReading.readToEnd() else { throw CommandError.readError } guard let output = String(data: data, encoding: .utf8) else { throw CommandError.invalidData } process.waitUntilExit() guard process.terminationStatus == 0 else { throw CommandError.commandFailed(output) } return output } when try to run "pgrep" in sandbox mode ON, i get: sysmon request failed with error: sysmond service not found error. if i turn it off it works. i don't know what to do. anyone can help me out?
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219
Mar ’25
Background Task Scheduling (BGAppRefreshTask)
All the nuances of when and whether a background task runs aside, does launching the app cancel the currently scheduled refresh task? As an example, consider the following case: 8AM - user launches app. This launch schedules a background refresh for 12 hours later, at 8PM 12PM (noon) - user launches the app, views some content, then exits the app. Does the scheduled refresh for 8PM still exist, or does the launch at noon invalidate that task, since the refresh could conceivably be handled during that noon launch? Hopefully this is articulated clearly enough, but I'm trying to understand the specifics of background refresh behavior, since I don't want to run that refresh every time the app is opened. However, if opening the app invalidates scheduled refreshes, I will need to include logic that will reschedule the refresh accordingly.
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486
Dec ’24
BGContinuedProcessingTask compatibility with background URLSession
My app does really large uploads. Like several GB. We use the AWS SDK to upload to S3. It seemed like using BGContinuedProcessingTask to complete a set of uploads for a particular item may improve UX as well as performance and reliability. When I tried to get BGContinuedProcessingTask working with the AWS SDK I found that the task would fail after maybe 30 seconds. It looked like this was because the app stopped receiving updates from the AWS upload and the task wants consistent updates. The AWS SDK always uses a background URLSession and this is not configurable. I understand the background URLSession runs in a separate process from the app and maybe that is why progress updates did not continue when the app was in the background. Is it expected that BGContinuedProcessingTask and background URLSession are not really compatible? It would not be shocking since they are 2 separate background APIs. Would the Apple recommendation be to use a normal URLSession for this, in which case AWS would need to change their SDK? Or does Apple think that BGContinuedProcessingTask should just not be used with uploads? In other words use an upload specific API. Thanks!
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130
Aug ’25
Electron app with Express + Python child processes not running in macOS production build
Hi all, I’ve built an Electron application that uses two child processes: An Express.js server A Python executable (packaged .exe/binary) During the development phase, everything works fine — the Electron app launches, both child processes start, and the app functions as expected. But when I create a production build for macOS, the child processes don’t run. Here’s a simplified snippet from my electron.mjs: import { app, BrowserWindow } from "electron"; import { spawn } from "child_process"; import path from "path"; let mainWindow; const createWindow = () => { mainWindow = new BrowserWindow({ width: 1200, height: 800, webPreferences: { nodeIntegration: true, }, }); mainWindow.loadFile("index.html"); // Start Express server const serverPath = path.join(process.resourcesPath, "app.asar.unpacked", "server", "index.js"); const serverProcess = spawn(process.execPath, [serverPath], { stdio: "inherit", }); // Start Python process const pythonPath = path.join(process.resourcesPath, "app.asar.unpacked", "python", "myapp"); const pythonProcess = spawn(pythonPath, [], { stdio: "inherit", }); serverProcess.on("error", (err) => console.error("Server process error:", err)); pythonProcess.on("error", (err) => console.error("Python process error:", err)); }; app.whenReady().then(createWindow); I’ve already done the following: Configured package.json with the right build settings Set up extraResources / asarUnpack to include the server and Python files Verified both child processes work standalone Questions: What’s the correct way to package and spawn these child processes for macOS production builds? Do I need to move them into a specific location (like Contents/Resources/app.asar.unpacked) and reference them differently? Is there a more reliable pattern for handling Express + Python child processes inside an Electron app bundle? Any insights or working examples would be really appreciated!
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63
Sep ’25
DispatchSourceTimer Not Firing in Local Push Connectivity Extension When App Is in Foreground and Device Is Locked
Hi, I’m using a Local Push Connectivity Extension and encountering an issue with DispatchSourceTimer. In my extension, I create a DispatchSourceTimer that is supposed to fire every 1 second. It works as expected at first. However, when the app is in the foreground and the device is locked, the timer eventually stops firing after 1–3 hours. The extension process is still alive, and no errors are thrown Has anyone experienced this behavior? Is this a known limitation for timers inside NEAppPushProvider, or is the extension being deprioritized silently by the system? Any insights or suggestions would be greatly appreciated. Thanks!
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82
Apr ’25
Background processing question
Hi, I have a hard time getting my head wrapped around the possibilities of running a app or a task in a app in the background. I have a app where I utilize MusicKit to create a playlist in Apple Music, and add songs to the playlist. Now the songs added are picked from choices made by the user, and the total number of songs to add is 75, and that takes some time. And if the user switches to a different app or the phone is locked, the add songs logic stops, and then starts again as soon as the app is active again. What I am trying to achieve is of course for this to keep processing also when the app is not active, so basically to keep it running in the background. But this is where I struggle to understand how I can do that - The available choice seems to be BGTaskScheduler, but that just does not seem correct. From what I understand it just schedules a task, and it will be processed whenever the app or phone "feels like it" (again, my understanding, might be wrong), and that won't work in my scenario. I want the task to start when the user taps a button, and just keep running until it is finished, regardless of if the app is active or not. Any pointers, tips, advices out there on how I can achieve this?
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77
Apr ’25
XPC codesign requirement crashes application
We have an application that sets a code signing requirement on a XPC connection between a File Provider extension and the main application. Only with a specific Developer ID certificate <DEVELOPER_ID_TEAM_IDENTIFIER> that designated requirement is not accepted and the application crashes with EXC_CRASH (SIGABRT) and the stacktrace Thread 1 Crashed:: Dispatch queue: com.apple.root.default-qos 0 libsystem_kernel.dylib 0x19b556388 __pthread_kill + 8 1 libsystem_pthread.dylib 0x19b58f88c pthread_kill + 296 2 libsystem_c.dylib 0x19b498a3c abort + 124 3 libc++abi.dylib 0x19b545384 abort_message + 132 4 libc++abi.dylib 0x19b533cf4 demangling_terminate_handler() + 344 5 libobjc.A.dylib 0x19b1b8dd4 _objc_terminate() + 156 6 libc++abi.dylib 0x19b544698 std::__terminate(void (*)()) + 16 7 libc++abi.dylib 0x19b547c30 __cxxabiv1::failed_throw(__cxxabiv1::__cxa_exception*) + 88 8 libc++abi.dylib 0x19b547bd8 __cxa_throw + 92 9 libobjc.A.dylib 0x19b1aecf8 objc_exception_throw + 448 10 Foundation 0x19d5c3840 -[NSXPCConnection setCodeSigningRequirement:] + 140 11 libxpcfileprovider.dylib 0x301023048 NSXPCConnection.setCodeSigningRequirementFromTeamIdentifier(_:) + 1796 12 libxpcfileprovider.dylib 0x30101dc94 closure #1 in CallbackFileProviderManager.getFileProviderConnection(_:service:completionHandler:interruptionHandler:exportedObject:) + 1936 13 libxpcfileprovider.dylib 0x30101e110 thunk for @escaping @callee_guaranteed @Sendable (@guaranteed NSXPCConnection?, @guaranteed Error?) -> () + 80 14 Foundation 0x19d46c3a4 __72-[NSFileProviderService getFileProviderConnectionWithCompletionHandler:]_block_invoke_2.687 + 284 15 libdispatch.dylib 0x19b3d7b2c _dispatch_call_block_and_release + 32 16 libdispatch.dylib 0x19b3f185c _dispatch_client_callout + 16 17 libdispatch.dylib 0x19b40e490 + 32 18 libdispatch.dylib 0x19b3e9fa4 _dispatch_root_queue_drain + 736 19 libdispatch.dylib 0x19b3ea5d4 _dispatch_worker_thread2 + 156 20 libsystem_pthread.dylib 0x19b58be28 _pthread_wqthread + 232 21 libsystem_pthread.dylib 0x19b58ab74 start_wqthread + 8 The designated codesign requirement on the XPC connection is set to anchor apple generic and certificate leaf[subject.OU] = <DEVELOPER_ID_TEAM_IDENTIFIER>" We have verified the designated code sign requirement to be valid on both the main bundle and the embedded extension using: codesign --verify -v -R '=anchor apple generic and certificate leaf[subject.OU] = "<DEVELOPER_ID_TEAM_IDENTIFIER>"' *.app codesign --verify -v -R '=anchor apple generic and certificate leaf[subject.OU] = "<DEVELOPER_ID_TEAM_IDENTIFIER>"' *.app/Contents/PlugIns/*
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102
Sep ’25
Using protocols with XPC C API instead of dictionaries for sending and receiving messages
I have followed this post for creating a Launch Agent that provides an XPC service on macOS using Swift- post link - https://rderik.com/blog/creating-a-launch-agent-that-provides-an-xpc-service-on-macos/ In the swift code the interface of the XPC service is defined by protocols which makes the code nice and neat. I want to implement the XPC service using C APIs for XPC, and C APIs send and receive messages using dictionaries, which need manual handling with conditional statements. I want to know if its possible to go with the protocol based approach with C APIs.
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469
Jan ’25
Keeping a socket connection active in app extension in a Safari Web Extension
I’m currently porting a Chrome Extension to Safari and integrating it with native messaging in a Safari Web Extension. As part of this, I’m building a proxy to forward messages between the web extension and a socket in another application, both ways. Additionally, the socket occasionally broadcasts messages that also need to be sent to the web extension. The issue I’m facing is that the app extension terminates whenever I call context.completeRequest(returningItems: nil), which prevents me from listening for incoming messages from the socket (I'm using the Network Framework). To work around this, I’ve tried not calling context.completeRequest(returningItems: nil), which keeps the app extension running. However, I’m unsure if this is the right approach—currently, I’m simply ignoring the response and relying entirely on SFSafariApplication.dispatchMessage. According to the documentation, the app extension lifecycle ends when the system terminates it, but I need to keep the socket listener active. Has anyone encountered a similar issue, or does anyone have suggestions for maintaining the socket connection while adhering to the app extension lifecycle? Any insights would be greatly appreciated!
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494
Jan ’25