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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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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244
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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197
Mar ’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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67
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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63
Apr ’25
earliestBeginDate timezone
I'm trying to schedule a background task that will run on an iPhone and I'm looking into creating a task request using BGProcessingTaskRequest and scheduled it using BGTaskScheduler.shared.submit(). Per earliestBeginDate documentation, this property can be used to specify the earliest time a background task will be launched by OS. All clear here. However, the question is: how is the value interpreted with respect to timezone ? Is the specified date in device timezone ? Is GMT ? Is something else ?
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54
Apr ’25
Help me implement SMAppServices
I have followed these steps as mentioned in this link :(https://developer.apple.com/forums/thread/721737) My projects app bundle structure is like this : TWGUI.app TWGUI.app/Contents TWGUI.app/Contents/_CodeSignature TWGUI.app/Contents/_CodeSignature/CodeResources TWGUI.app/Contents/MacOS TWGUI.app/Contents/MacOS/TWAgent TWGUI.app/Contents/MacOS/TWGUI TWGUI.app/Contents/Resources TWGUI.app/Contents/Library TWGUI.app/Contents/Library/LaunchAgents TWGUI.app/Contents/Library/LaunchAgents/com.example.TWGUI.agent.plist TWGUI.app/Contents/Info.plist TWGUI.app/Contents/PkgInfo TWGUI is my main GUI App , i which i want to embed TWAgent (a command line tool target) and register it using SMAppServices so that launchd can launch it. In TWGUI, code for registering to launchd using SMAppServices is structure as follow : import SwiftUI import ServiceManagement struct ContentView: View { let agent = SMAppService.agent(plistName: "com.example.TWGUI.agent.plist") var body: some View { VStack { Button("Register Agent") { RegisterAgent () } .padding() Button("Unregister Agent") { UnregisterAgent () } .padding() } } func RegisterAgent() { DispatchQueue.global(qos: .background).async { do { print("Registering Agent. Status: \(agent.status.rawValue)") try agent.register() print("Agent registered") } catch { print("Failed to register agent: \(error)") } } } func UnregisterAgent() { DispatchQueue.global(qos: .background).async { do { print("Unregistering Agent. Status: \(agent.status.rawValue)") try agent.unregister() print("Agent unregistered") } catch { print("Failed to unregister agent: \(error)") } } } } com.example.TWGUI.agent.plist : <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs$ <plist version="1.0"> <dict> <key>Label</key> <string>com.example.TWGUI.agent</string> <key>ProgramArguments</key> <array> <string>Contents/MacOS/TWAgent</string> </array> <key>RunAtLoad</key> <true/> <key>KeepAlive</key> <true/> </dict> </plist> I have used ProgramArguements instead of using Program in above plist because i was getting this error when i was using Program earlier : Registering Agent. Status: 3 Failed to register agent: Error Domain=SMAppServiceErrorDomain Code=111 "Invalid or missing Program/ProgramArguments" UserInfo={NSLocalizedFailureReason=Invalid or missing Program/ProgramArguments} TWGUI apps Info.plist is : <?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>BuildMachineOSBuild</key> <string>23C71</string> <key>CFBundleDevelopmentRegion</key> <string>en</string> <key>CFBundleExecutable</key> <string>TWGUI</string> <key>CFBundleIdentifier</key> <string>com.example.TWAgent</string> <key>CFBundleInfoDictionaryVersion</key> <string>6.0</string> <key>CFBundleName</key> <string>TWGUI</string> <key>CFBundlePackageType</key> <string>APPL</string> <key>CFBundleShortVersionString</key> <string>1.0</string> <key>CFBundleSupportedPlatforms</key> <array> <string>MacOSX</string> </array> <key>CFBundleVersion</key> <string>1</string> <key>DTCompiler</key> <string>com.apple.compilers.llvm.clang.1_0</string> <key>DTPlatformBuild</key> <string></string> <key>DTPlatformName</key> <string>macosx</string> <key>DTPlatformVersion</key> <string>14.2</string> <key>DTSDKBuild</key> <string>23C53</string> <key>DTSDKName</key> <string>macosx14.2</string> <key>DTXcode</key> <string>1510</string> <key>DTXcodeBuild</key> <string>15C65</string> <key>LSMinimumSystemVersion</key> <string>14.2</string> </dict> </plist> TWAgent target has main.swift file which does this : import Foundation let startTime = CFAbsoluteTimeGetCurrent() func logTimeSinceStart() { let elapsedTime = CFAbsoluteTimeGetCurrent() - startTime NSLog("Time since program started: \(elapsedTime) seconds") } func startLoggingTime() { Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { _ in logTimeSinceStart() } } // Start logging time startLoggingTime() // Keep the run loop running CFRunLoopRun() I followed these exact same steps in another project earlier and my agent was getting registered, although i lost that project due to some reasons. But now i am getting this error when i am registering or unregistering agent using SMAppServices from the code above : Registering Agent. Status: 3 Failed to register agent: Error Domain=SMAppServiceErrorDomain Code=1 "Operation not permitted" UserInfo={NSLocalizedFailureReason=Operation not permitted} I tried diffrent fixes for like this : Moved app bundle to /applications folder Gave permission for full disc access to this app . Code sign again (both agent and TWGUI ... But nothing seems to work , getting same error. I tried to launch agent using : Launchctl load com.example.TWGUI.agent.plist and it worked , so there is no issue with my plist implementation. Can someone help me understand how can i solve this issue ? or if i am following right steps ? Can give steps need to follow to implement this and steps so that i can register and start my agent using SMAppServices? And i also tried the project give in apples official documentation : [https://developer.apple.com/documentation/servicemanagement/updating-your-app-package-installer-to-use-the-new-service-management-api) but got same error in this project as well .
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Apr ’25
Launch Host App from Share Extension
Hi! Could you please point me to the official documentation or recommended approach for launching the host app from a Share Extension? The scenario is: The user is sharing some text to my app. I need launch App and show this text. At the moment, I'm using the following hack: let selector = NSSelectorFromString("sharedApplication") if let app = UIApplication.perform(selector)?.takeUnretainedValue() as? UIApplication, app.responds(to: #selector(UIApplication.open(_:options:completionHandler:))) { app.open(url, options: [:], completionHandler: nil) } This does work, but it's terrible. So, the question: What is the official way to open the host app from within a Share Extension? Thanks!
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113
Apr ’25
Working with Input/Output stream with Swift 6 and concurrency framework
Hello, I am developing an application which is communicating with external device using BLE and L2CAP. I wonder what are the best practices of using Input & Output streams that are established with L2CAP connection when working with Swift 6 concurrency model. I've been trying to find some examples and hints for some time now but unfortunately there isn't much available. One useful thread I've found is: https://developer.apple.com/forums/thread/756281 but it does not offer much insight into using eg. actor model with streams. I wonder if something has changed in this regards? Also, are there any plans to migrate eg. CoreBluetooth stack to new swift 6 concurrency ?
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96
Apr ’25
Question about BGAppRefreshTask approach for medication scheduling app
I'm developing a medication scheduling app similar to Apple Health's Medications feature, and I'd like some input on my current approach to background tasks. In my app, when a user creates a medication, I generate ScheduledDose objects (with corresponding local notifications) for the next 2 weeks and save them to SwiftData. To ensure this 2-week window stays current, I've implemented a BGAppRefreshTask that runs daily to generate new doses as needed. My concern is whether BGAppRefreshTask is the appropriate mechanism for this purpose. Since I'm not making any network requests but rather generating and storing local data, I'm questioning if this is the right approach. I'm also wondering how Apple Health's Medications feature handles this kind of scheduling. Their app seems to maintain future doses regardless of app usage patterns. Has anyone implemented something similar or can suggest the best background execution API for this type of scenario? Thanks for any guidance you can provide.
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111
Apr ’25
Background Assets Extension and DeviceCheck
Hi, I have some questions regarding the Background Assets Extension and DeviceCheck framework. Goal: Ensure that only users who have purchased the app can access the server's API without any user authentication using for example DeviceCheck framework and within a Background Assets Extension. My app relies on external assets, which I'm loading using the Background Assets Extension. I'm trying to determine if it's possible to obtain a challenge from the server and send a DeviceCheck assertion during this process within the Background Assets Extension. So far, I only receive session-wide authentication challenges—specifically NSURLAuthenticationMethodServerTrust in the Background Assets Extensio. I’ve tested with Basic Auth (NSURLAuthenticationMethodHTTPBasic) just for experimentation, but the delegate func backgroundDownload( _ download: BADownload, didReceive challenge: URLAuthenticationChallenge ) async -> (URLSession.AuthChallengeDisposition, URLCredential?) is never called with that authentication method. It seems task-specific challenges aren't coming through at all. Also, while the DCAppAttestService API appears to be available on macOS, DCAppAttestService.isSupported always returns false (in my testing), which suggests it's not actually supported on macOS. Can anyone confirm if that’s expected behavior?
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99
May ’25
Is there an API to programmatically obtain an XPC Service's execution context?
Hello! I'm writing a System Extension that is an Endpoint Security client. And I want to Deny/Allow executing some XPC Service processes (using the ES_EVENT_TYPE_AUTH_EXEC event) depending on characteristics of a process that starts the XPC Service. For this purpose, I need an API that could allow me to obtain an execution context of the XPC Service process. I can obtain this information using the "sudo launchctl procinfo <pid>" command (e.g. I can use the "domain = pid/3428" part of the output for this purpose). Also, I know that when the xpcproxy process is started, it gets as the arguments a service name and a pid of the process that requests the service so I can grasp the execution context from xpcproxy launching. But are these ways to obtain this info legitimate?
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143
Apr ’25
SMAppService getting notified when status changes externally (from System Settings)
Say I want to sync a toggle in my app with SMAppService's .status property. If the status changes from my app I can track it. But if user toggles it from System Settings, I don't see a notification so then the UI in my app is out of date. The status property is not key value observable and there doesn't appear to be a SMAppServiceStatusDidChangeNotification ? I can re-read it every time my app will become active but feels kind of wrong to do it this way.
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56
May ’25
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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238
Jul ’25
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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87
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 = () =&gt; { 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) =&gt; console.error("Server process error:", err)); pythonProcess.on("error", (err) =&gt; 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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2w
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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3d
Called endBackgroundTask but not working
When my app enter to background, I start a background task, and when Expiration happens, I end my background task. The code likes below: backgroundTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{ dispatch_async(dispatch_get_main_queue(), ^{ if (backgroundTask != UIBackgroundTaskInvalid) { [[UIApplication sharedApplication] endBackgroundTask:backgroundTask]; backgroundTask = UIBackgroundTaskInvalid; [self cancel]; } }); }]; When the breakpoint is triggered at the endBackgroundTask line, I also get the following log: [BackgroundTask] Background task still not ended after expiration handlers were called: <UIBackgroundTaskInfo: 0x282d7ab40>: taskID = 36, taskName = Called by MyApp, from MyMethod, creationTime = 892832 (elapsed = 26). This app will likely be terminated by the system. Call UIApplication.endBackgroundTask(:) to avoid this. The log don't appear every time, so why is that? Is there something wrong with my code?
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2.8k
Jun ’25
Are XPCSession and XPCListener incomplete(ly documented)?
I've been experimenting with the new low-level Swift API for XPC (XPCSession and XPCListener). The ability to send and receive Codable messages is an appealing alternative to making an @objc protocol in order to use NSXPCConnection from Swift — I can easily create an enum type whose cases map onto the protocol's methods. But our current XPC code validates the incoming connection using techniques similar to those described in Quinn's "Apple Recommended" response to the "Validating Signature Of XPC Process" thread. I haven't been able to determine how to do this with XPCListener; neither the documentation nor the Swift interface have yielded any insight. The Creating XPC Services article suggests using Xcode's XPC Service template, which contains this code: let listener = try XPCListener(service: serviceName) { request in request.accept { message in performCalculation(with: message) } } The apparent intent is to inspect the incoming request and decide whether to accept it or reject it, but there aren't any properties on IncomingSessionRequest that would allow the service to make that decision. Ideally, there would be a way to evaluate a code signing requirement, or at least obtain the audit token of the requesting process. (I did notice that a function xpc_listener_set_peer_code_signing_requirement was added in macOS 14.4, but it takes an xpc_listener_t argument and I can't tell whether XPCListener is bridged to that type.) Am I missing something obvious, or is there a gap in the functionality of XPCListener and IncomingSessionRequest?
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928
Feb ’25