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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Cleanup LaunchAgents after development
I have been playing with application bundled LaunchAgents: I downloaded Apple sample code, Run the sample code as is, Tweaked the sample code a lot and changed the LaunchAgents IDs and Mach ports IDs, Created new projects with the learnings, etc. After deleting all the Xcode projects and related project products and rebooting my machine several times, I noticed the LaunchAgent are still hanging around in launchctl. If I write launchctl print-disabled gui/$UID (or user/$UID) I can see all my testing service-ids: disabled services = { "com.xpc.example.agent" => disabled "io.dehesa.apple.app.agent" => disabled "io.dehesa.sample.app.agent" => disabled "io.dehesa.example.agent" => disabled "io.dehesa.swift.xpc.updater" => disabled "io.dehesa.swift.agent" => disabled } (there are more service-ids in that list, but I removed them for brevity purposes). I can enable or disable them with launchctl enable/disable service-target, but I cannot really do anything else because their app bundle and therefore PLIST definition are not there anymore. How can I completely remove them from my system? More worryingly, I noticed that if I try to create new projects with bundled LaunchAgents and try to reuse one of those service-ids, then the LaunchAgent will refuse to run (when it was running ok previously). The calls to SMAppService APIs such .agent(plistName:) and register() would work, though.
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May ’25
How is BGContinuedProcessingTask intended to be used?
Hello, I'm trying to adopt the new BGContinuedProcessingTask API, but I'm having a little trouble imagining how the API authors intended it be used. I saw the WWDC talk, but it lacked higher-level details about how to integrate this API, and I can't find a sample project. I notice that we can list wildcard background task identifiers in our Info.plist files now, and it appears this is to be used with continued tasks - a user might start one video encoding, then while it is ongoing, enqueue another one from the same app, and these tasks would have identifiers such as "MyApp.VideoEncoding.ABCD" and "MyApp.VideoEncoding.EFGH" to distinguish them. When it comes to implementing this, is the expectation that we: a) Register a single handler for the wildcard pattern, which then figures out how to fulfil each request from the identifier of the passed-in task instance? Or b) Register a unique handler for each instance of the wildcard pattern? Since you can't unregister handlers, any resources captured by the handler would be leaked, so you'd need to make sure you only register immediately before submission - in other words register + submit should always be called as a pair. Of course, I'd like to design my application to use this API as the authors intended it be used, but I'm just not entirely sure what that is. When I try to register a single handler for a wildcard pattern, the system rejects it at runtime (while allowing registrations for each instance of the pattern, indicating that at least my Info.plist is configured correctly). That points towards option B. If it is option B, it's potentially worth calling that out in documentation - or even better, perhaps introduce a new call just for BGContinuedProcessingTask instead of the separate register + submit calls? Thanks for your insight. K Aside: Also, it would be really nice if the handler closure would be async. Currently if you need to await on something, you need to launch an unstructured Task, but that causes issues since BGContinuedProcessingTask is not Sendable, so you can't pass it in to that Task to do things like update the title or mark the BGTask as complete.
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Schedule BGAppRefreshTask more often for debugging purposes
I am considering to use the BGAppRefreshTask mechanism, and while I think I have read and understood all documentation and hints in this forum about it (especially the limitations), the one thing I do not understand is: how can I debug it? I cannot find a way to trigger the BGAppRefreshTask execution reliably and immediately. I would have expected the Xcode Debug->Simulate Background Fetch menu to do this for me, but it only sends the app into the background. I am working with the unmodified (except for a few added print()) ColorFeed sample code project from Apple, which schedules a task 15min into the future when it goes to the background. Using a real device, I have not managed to trigger execution of the BGAppRefreshTask more often than once a day so far. Surely, there must be a way to trigger it much more often solely for debugging and development purposes (I am totally happy with all restrictions for the final app). So what detail am I missing here?
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527
Jan ’25
Re-enrolling a LaunchDaemon, does it require user auth?
I am building an app that uses the SMAppService to register a LaunchDaemon that is bundled with my .app. I've got a priming flow created which walks the user through approving the service so that it will start on login. However, I need to also be able to upgrade this background service if the user updates the app. To do this, I think I need to call unregisterAndReturnError and then registerAndReturnError. From my testing, this seems to work correctly, but I have a concern. Will the user ever be prompted to re-authorize the LaunchDaemon that I am registering? If so, under what circumstances will that happen, and what does it look like (so that I can guide the user through it)?
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May ’25
LaunchAgent can't connect to CloudKit daemon
For this code: let status = try await container.accountStatus() Seeing this error: 2025-05-08 15:32:00.945731-0500 localhost myAgent[2661]: (myDaemon.debug.dylib) [com.myDaemon.cli:networking] Error Domain=CKErrorDomain Code=6 "Error connecting to CloudKit daemon. This could happen for many reasons, for example a daemon exit, a device reboot, a race with the connection inactivity monitor, invalid entitlements, and more. Check the logs around this time to investigate the cause of this error." UserInfo={NSLocalizedDescription=Error connecting to CloudKit daemon. This could happen for many reasons, for example a daemon exit, a device reboot, a race with the connection inactivity monitor, invalid entitlements, and more. Check the logs around this time to investigate the cause of this error., CKRetryAfter=5, CKErrorDescription=Error connecting to CloudKit daemon. This could happen for many reasons, for example a daemon exit, a device reboot, a race with the connection inactivity monitor, invalid entitlements, and more. Check the logs around this time to investigate the cause of this error., NSUnderlyingError=0x600001bfc270 {Error Domain=NSCocoaErrorDomain Code=4099 UserInfo={NSDebugDescription= I initially started the this process as System Daemon to see what would happen (which obviously does not have CloudKit features). Then moved it back to /Library/LaunchAgents/ and can't get rid of that error. I see also following message from CloudKit daemon: Ignoring failed attempt to get container proxy for <private>: Error Domain=NSCocoaErrorDomain Code=4099 UserInfo={NSDebugDescription=<private>} Automatically retrying getting container proxy due to error for <private>: Error Domain=NSCocoaErrorDomain Code=4099 UserInfo={NSDebugDescription=<private>} XPC connection interrupted for <private> And this error for xpc service: [0x130e074b0] failed to do a bootstrap look-up: xpc_error=[3: No such process] If I start the same cli process directly from XCode, then it works just fine.
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130
May ’25
SMAppService - How does this work?
I'm a developer using Lazarus Pascal, so converting ObjC and Swift comes with its challenges. I'm trying to figure how to properly use SMAppService to add my application as a login item for the App Store. I have learned that the old method (< macOS 13) uses a helper tool, included in the app bundle, which calls the now deprecated SMLoginItemSetEnabled. Now this is already quite a pain to deal with if you're not using XCode, not to mention converting the headers being rather complicated when you're not experienced with doing this. The "new" method (as of macOS 13) is using SMAppService. Can anyone explain how to use this? The documentation (for me anyway) is a not very clear about that and neither are examples that can be found all over the Internet. My main question is: Can I now use the SMAppService functions to add/remove a login item straight in my application, or is a helper tool still required?
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134
Mar ’25
SMAppService Sample Code seems broken
I abandoned Mac development back around 10.4 when I departed Apple and am playing catch-up, trying to figure out how to register a privileged helper tool that can execute commands as root in the new world order. I am developing on 13.1 and since some of these APIs debuted in 13, I'm wondering if that's ultimately the root of my problem. Starting off with the example code provided here: https://developer.apple.com/documentation/servicemanagement/updating-your-app-package-installer-to-use-the-new-service-management-api Following all build/run instructions in the README to the letter, I've not been successful in getting any part of it to work as documented. When I invoke the register command the test app briefly appears in System Settings for me to enable, but once I slide the switch over, it disappears. Subsequent attempts to invoke the register command are met only with the error message: `Unable to register Error Domain=SMAppServiceErrorDomain Code=1 "Operation not permitted" UserInfo={NSLocalizedFailureReason=Operation not permitted} The app does not re-appear in System Settings on these subsequent invocations. When I invoke the status command the result mysteriously equates to SMAppService.Status.notFound. The plist is in the right place with the right name and it is using the BundleProgram key exactly as supplied in the sample code project. The executable is also in the right place at Contents/Resources/SampleLaunchAgent relative to the app root. The error messaging here is extremely disappointing and I'm not seeing any way for me to dig any further without access to the underlying Objective-C (which the Swift header docs reference almost exclusively, making it fairly clear that this was a... Swift... Port... [Pun intended]).
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235
Sep ’25
Check whether XPC remote proxy responds to selector, without causing exception and connection invalidation?
I have several processes maintaining NSXPConnection to an XPC service. The connections are bi-directional. Each side service and clients) of the connection exports an object, and an XPCInterface. The @protocols are different - to the service, and from the service to clients. So long as all the "clients" fully implement their "call-back" @protocol, there's no problem. All works fine. However - If a client does NOT implement a method in the "call back protocol", or completely neglects to export an object, or interface - and the service attempts to call back using the nonexistent method -- the XPC connection invalidates immediately. So far - expected behaviour. However, if I want the service to behave to the client a little like a "delegate" style -- and check first whether the client "respondsToSelector" or even - supports an interface BEFORE calling it, then this doesn't work. When my XPC service tries the following on a client connection: if (xpcConnection.remoteObjectInterface == nil) os_log_error(myXPCLog, "client has no remote interface); the condition is never met - i.e. the "remoteObjectInterface is never nil even when the client does NOT configure its NSXPCConnection with any incoming NSXPCInterface, and does not set an "exportedObject" Furthermore, the next check: if ([proxy respondsToSelector:@selector(downloadFiltersForCustomer:withReply:)]) { } will not only fail - but will drop the connection. The client side gets the invalidation with the following error: <NSXPCConnection: 0x600000b20000> connection to service with pid 2477 named com.proofpoint.ecd: received an undecodable message for proxy 1 (no exported object to receive message). Dropping message. I guess the "undecidable message" is the respondsToSelector - because the code doesn't get to attempt anything else afterwards, the connection drops. Is there a way to do this check "quietly", or suffering only "interruption", but without losing the connection,
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Jan ’25
Do i need to free memory for C strings obtained from xpc_dictionary_get_string?
I am using C APIs for XPC communication. When my XPC server gets a xpc_dictionary as a message, I use xpc_dictionary_get_string to get the string which is of type const char*. Afterwards, when I try to free up the memory for the string, I get an error. I could not find any details on why this happens. Does XPC handle the lifecycle of these C strings ? I did some tests to see the behaviour. The following code snippet prints a string temp before and after releasing the dictionary memory. char* string = "dummy-string"; xpc_object_t dict = xpc_dictionary_create(NULL, NULL, 0); xpc_dictionary_set_string(dict, "str", string); const char* temp = xpc_dictionary_get_string(reply, "str"); printf("temp before release: %s\n", temp); xpc_release(reply); printf("temp after release: %s\n", temp); output: # temp before release: dummy-string # temp after release: I tried to free the variable temp before and after releasing dict . char* string = "dummy-string"; xpc_object_t dict = xpc_dictionary_create(NULL, NULL, 0); xpc_dictionary_set_string(dict, "str", string); const char* temp = xpc_dictionary_get_string(dict, "str"); printf("temp before release: %s\n", temp); free((void *)temp); // case 1 xpc_release(dict); // free((void *)temp); // case 2 printf("temp after release: %s\n", temp); in both the cases i got the output: # temp before release: dummy-string # app(18502,0x1f02fc840) malloc: Double free of object 0x145004a20 # app(18502,0x1f02fc840) malloc: *** set a breakpoint in malloc_error_break to debug # SIGABRT: abort # PC=0x186953720 m=0 sigcode=0 # signal arrived during cgo execution # ... # ...
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Feb ’25
best practices for communication between system extension and daemon
Hello, My team has developed a DNS proxy for macOS. We have this set up with a system extension that interacts with the OS, and an always-running daemon that does all the heavy lifting. Communication between the two is DNS request and response packet traffic. With this architecture what are best practices for how the system extension communicates with a daemon? We tried making the daemon a socket server, but the system extension could not connect to it. We tried using XPC but it did not work and we could not understand the errors that were returned. So what is the best way to do this sort of thing?
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724
Jan ’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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May ’25
Getting Progress from long running process
I have been working on updating an old app that makes extensive use of Objective-C's NSTask. Now using Process in Swift, I'm trying to gather updates as the process runs, using readabilityHandler and availableData. However, my process tends to exit before all data has been read. I found this post entitled "Running a Child Process with Standard Input and Output" but it doesn't seem to address gathering output from long-running tasks. Is there a straightforward way to gather ongoing output from a long running task without it prematurely exiting?
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155
May ’25
XPC activity doesn’t fire while main app is closed
Hi, I have a sandboxed app with a bundled sandboxed XPC service. When it’s launched, the XPC service registers a repeating XPC activity with the system. The activity’s handler block does get called regularly like I’d expect, but it stops being called once the main app terminates. What’s the recommended way to fix this issue? Could I have a bundled XPC service double as a launch agent, or would that cause other problems?
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136
May ’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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Apr ’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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Jan ’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
Are iPad apps that are closed with the red traffic light prevented from running background tasks?
In iOS Background Execution limits, I see this: When the user ‘force quits’ an app by swiping up in the multitasking UI, iOS interprets that to mean that the user doesn’t want the app running at all. iOS also sets a flag that prevents the app from being launched in the background. That flag gets cleared when the user next launches the app manually. However, I see that when I close an app on iPadOS 26 with the red X, the app doesn't appear in the multitasking UI. So are they treated as force closes and prevented from running background tasks?
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95
Sep ’25
Cross process URL bookmark
I am developing a background application that acts as a metadata server under MacOS written in Swift. Sandboxed clients prompt the user to select URLs which are passed to the server as security scoped bookmarks via an App Group and the metadata will be passed back. I don't want the I/O overhead of passing the complete image file data to the server. All the variations I have tried of creating security scoped bookmarks in the client and reading them from the server fail with error messages such as "The file couldn’t be opened because it isn’t in the correct format." Can anyone guide me in the right direction or is this just not possible?
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174
Jun ’25
How to prevent the main app from being terminated by the system during long - term system - level recording
After logging in to the main App, turn on screen recording, then switch to the interface of another App to perform operations. After about ten-odd minutes, when returning to the main App, it was found that the app was forcefully quit by the system, and subsequent operations could not be carried out.
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90
May ’25
Background App Refresh
Hi, I have a couple questions about background app refresh. First, is the function RefreshAppContentsOperation() where to implement code that needs to be run in the background? Second, despite importing BackgroundTasks, I am getting the error "cannot find operationQueue in scope". What can I do to resolve that? Thank you. func scheduleAppRefresh() { let request = BGAppRefreshTaskRequest(identifier: "peaceofmindmentalhealth.RoutineRefresh") // Fetch no earlier than 15 minutes from now. request.earliestBeginDate = Date(timeIntervalSinceNow: 15 * 60) do { try BGTaskScheduler.shared.submit(request) } catch { print("Could not schedule app refresh: \(error)") } } func handleAppRefresh(task: BGAppRefreshTask) { // Schedule a new refresh task. scheduleAppRefresh() // Create an operation that performs the main part of the background task. let operation = RefreshAppContentsOperation() // Provide the background task with an expiration handler that cancels the operation. task.expirationHandler = { operation.cancel() } // Inform the system that the background task is complete // when the operation completes. operation.completionBlock = { task.setTaskCompleted(success: !operation.isCancelled) } // Start the operation. operationQueue.addOperation(operation) } func RefreshAppContentsOperation() -> Operation { }
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473
Oct ’25