Processes & Concurrency

RSS for tag

Discover how the operating system manages multiple applications and processes simultaneously, ensuring smooth multitasking performance.

Concurrency Documentation

Posts under Processes & Concurrency subtopic

Post

Replies

Boosts

Views

Activity

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.
2
0
507
Jan ’25
dispatch_main and main thread local variables
Hello, We're seeing some strange crashes and noticed the following. It's unclear if related or not. The contract for xpc_main, which internally calls dispatch_main, is This function never returns. and they are appropriately peppered with __attribute__((__noreturn__)). Documentation states: This function “parks” the main thread and waits for blocks to be submitted to the main queue. However, internally, dispatch_main calls pthread_exit. pthread_exit's documentation states that: After a thread has terminated, the result of access to local (auto) variables of the thread is undefined. Thus, references to local variables of the exiting thread should not be used for the pthread_exit() value_ptr parameter value. I'd say the two contracts of This function never returns. and thread exiting with its storage released are diametrically opposed and can create nuanced issues. Consider the following code: struct asd { int a; }; struct asd* ptr; void fff(void* ctx) { while(true) { printf("%d\n", ptr->a); ptr->a = (ptr->a + 1); usleep(100000); } } int main(int argc, const char * argv[]) { struct asd zxc; zxc.a = 1; ptr = &zxc; dispatch_async_f(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), NULL, fff); dispatch_main(); return 0; } This is a gross over-simplification of the code we have, but in the same "spirit". We have a C++ object that is created on the stack and exposes one of its members as a global pointer, with the assumption that it would never release. What I understand from This function never returns is that the calling thread remains dormant and its stack remains alive. What I understand from pthread_exit is that the thread is killed (this is verified with a debugger attached) and its stack storage is released. Another thing that is throwing me off is that no sanitizer that is provided by clang/Xcode catches this issue. I don't see any special handling of the internal pthread_t in libdispatch to keep the stack storage alive. Our code is more complex, but can be solved by allocating the initial object on the heap, rather than on the stack. But still I would like to understand if this is the expected behavior. Perhaps my preconception of __attribute__((__noreturn__)) is wrong, and accessing stack variables post call to a __attribute__((__noreturn__)) function is UB? Thanks
1
0
121
Jul ’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?
3
0
143
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?
1
0
108
Mar ’25
BGTaskScheduler fails to match unique identifiers to a registered wildcard handler for BGContinuedProcessingTask
Testing Environment: iOS Version: 26.0 Beta 7 Xcode Version: 17.0 Beta 6 Device: iPhone 16 Pro Description: We are implementing the new BGContinuedProcessingTask API and are using the wildcard identifier notation as described in the official documentation. Our Info.plist is correctly configured with a permitted identifier pattern, such as com.our-bundle.export.*. We then register a single launch handler for this exact wildcard pattern. We are performing this registration within a UIViewController, which is a supported pattern as BGContinuedProcessingTask is explicitly exempt from the "register before applicationDidFinishLaunching" requirement, according to the BGTaskScheduler.h header file. The register method correctly returns true, indicating the registration was successful. However, when we then try to submit a task with a unique identifier that matches this pattern (e.g., com.our-bundle.export.UUID), the BGTaskScheduler.shared.submit() call throws an NSInternalInconsistencyException and terminates the app. The error reason is: 'No launch handler registered for task with identifier com.our-bundle.export.UUID'. This indicates that the system is not correctly matching the specific, unique identifier from the submit call to the registered wildcard pattern handler. This behavior contradicts the official documentation. Steps to Reproduce: Create a new Xcode project. In Signing & Capabilities, add "Background Modes" (with "Background processing" checked) and "Background GPU Access". Add a permitted identifier (e.g., "com.company.test.*") to BGTaskSchedulerPermittedIdentifiers in Info.plist. In a UIViewController's viewDidLoad, register a handler for the wildcard pattern. Check that the register method returns true. Immediately after, try to submit a BGContinuedProcessingTaskRequest with a unique identifier that matches the pattern. Expected Results: The submit call should succeed without crashing, and the task should be scheduled. Actual Results: The app crashes immediately upon calling submit(). The console shows an uncaught NSInternalInconsistencyException with the reason: 'No launch handler registered for task with identifier com.company.test.UUID'. Workaround: The issue can be bypassed if we register a new handler for each unique identifier immediately before submitting a request with that same unique identifier. This strongly suggests the bug is in the system's wildcard pattern-matching logic.
1
0
127
Sep ’25
Helper app is sandboxed (entitlement + runtime check), but `URLsForDirectory:` returns user home (`/Users//`) instead of container path — why?
Problem summary I have a macOS helper app that is launched from a sandboxed main app. The helper: has com.apple.security.app-sandbox = true and com.apple.security.inherit = true in its entitlements, is signed and embedded inside the main app bundle (placed next to the main executable in Contents/MacOS), reports entitlement_check = 1 (code signature contains sandbox entitlement, implemented via SecStaticCode… check), sandbox_check(getpid(), NULL, 0) returns 1 (runtime sandbox enforcement present), APP_SANDBOX_CONTAINER_ID environment variable is not present (0). Despite that, Cocoa APIs return non-container home paths: NSHomeDirectory() returns /Users/<me>/ (the real home). [[NSFileManager defaultManager] URLsForDirectory:inDomains:] and URLForDirectory:inDomain:appropriateForURL:create:error: return paths rooted at /Users/<me>/ (not under ~/Library/Containers/<app_id>/Data/...) — i.e. they look like non-sandboxed locations. However, one important exception: URLForDirectory:... for NSItemReplacementDirectory (temporary/replacement items) does return a path under the helper's container (example: ~/Library/Containers/<app_id>/Data/tmp/TemporaryItems/NSIRD_<helper_name>_hfc1bZ). This proves the sandbox is active for some FileManager APIs, yet standard directory lookups (Application Support, Documents, Caches, and NSHomeDirectory()) are not being redirected to the container. What I expect The helper (which inherits the sandbox and is clearly sandboxed) should get container-scoped paths from Cocoa’s FileManager APIs (Application Support, Documents, Caches), i.e. paths under the helper’s container: /Users/<me>/Library/Containers/<app_id>/Data/.... What I tried / diagnostics already gathered Entitlements & code signature codesign -d --entitlements :- /path/to/Helper.app/Contents/MacOS/Helper # shows com.apple.security.app-sandbox = true and com.apple.security.inherit = true Runtime checks (Objective-C++ inside helper): extern "C" int sandbox_check(pid_t pid, const char *op, int flags); NSLog(@"entitlement_check = %d", entitlement_check()); // SecStaticCode check NSLog(@"env_variable_check = %d", (getenv("APP_SANDBOX_CONTAINER_ID") != NULL)); NSLog(@"runtime_sandbox_check = %d", sandbox_check(getpid(), nullptr, 0)); NSLog(@"NSHomeDirectory = %s", NSHomeDirectory()); NSArray *urls = [[NSFileManager defaultManager] URLsForDirectory:NSApplicationSupportDirectory inDomains:NSUserDomainMask]; NSLog(@"URLsForDirectory: %@", urls); Observed output: entitlement_check = 1 env_variable_check = 0 runtime_sandbox_check = 1 NSHomeDirectory = /Users/<me> URLsForDirectory: ( "file:///Users/<me>/Library/Application%20Support/..." ) Temporary/replacement directory (evidence sandbox active for some APIs): NSURL *tmpReplacement = [[NSFileManager defaultManager] URLForDirectory:NSItemReplacementDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:YES error:&err]; NSLog(@"NSItemReplacementDirectory: %@", tmpReplacement.path); Observed output (example): /Users/<me>/Library/Containers/<app_id>/Data/tmp/TemporaryItems/NSIRD_<helper_name>_hfc1bZ Other facts Calls to NSHomeDirectory() and URLsForDirectory: are made after main() to avoid "too early" initialization problems. Helper is placed in Contents/MacOS (not Contents/Library/LoginItems). Helper is a non-GUI helper binary launched by the main app (not an XPC service). macOS version: Sequoia 15.6 Questions Why do NSHomeDirectory() and URLsForDirectory: return the real /Users/<me>/... paths in a helper process that is clearly sandboxed (entitlement + runtime enforcement), while NSItemReplacementDirectory returns a container-scoped temporary path? Is this behavior related to how the helper is packaged or launched (e.g., placement in Contents/MacOS vs Contents/Library/LoginItems, or whether it is launched with posix_spawn/fork+exec vs other APIs)? Are there additional entitlements or packaging rules required for a helper that inherits sandbox to have Cocoa directory APIs redirected to the container (for Application Support, Documents, Caches)? *Thanks in advance — I can add any requested logs
6
0
158
Sep ’25
Launch daemon running but XPC is down
Hello, I have a question about a edge case scenario. Before that some info on my project- I have a launchdaemon that carries out some business logic, it also has XPC listener (built using C APIs). Question- Can there be a situation when the daemon is up and running but the XPC listener is down(due to some error or crash)? If yes then do I need to handle it in my code or launchd will handle it? when the daemon is stopped or shut down, how do I stop the XPC listener? After getting listener object from xpc_connection_create_mach_service should I just call xpc_connection_cancel followed by a call to xpc_release? Thanks! K
3
0
139
Apr ’25
mac 开发 com.apple.security.application-groups 问题
我在开发 Mac应用完成 后 通过Xcode 上传二进制文件的过程中, 出现了错误, 错误提示: App里面用到的 com.apple.security.application-groups 权限里面 有 group.*** 和 开发者组ID.*** 导致校验失败, 当我单独使用 group.xxx的时候, 我的程序会崩溃 , 因为里面用到了 MachPortRende 进程间通信问题, 这里默认了 开发者组ID.*** 这个路径, 错误详情: 在尝试启动 QuickFox 应用时,程序因权限问题而崩溃。具体的错误信息 bootstrap_check_in 组ID.xxxx.MachPortRendezvousServer.82392: Permission denied (1100) 显示,应用在尝试使用 Mach 端口进行进程间通信时,没有获得足够的权限, 因此 我需要您们的帮助, 如果单独用开发者组ID.*** 我们又没有权限 将数据写入 组ID.xxx里面的文件
1
0
101
Apr ’25
XPC Service Installed Outside App Doesn't Set Responsible
On macOS 15.7.1 I'm trying to install an XPC service outside the app (Developer ID). It mostly seems to go ok, but when I set Launch Constraints on Responsible, AMFI complains of a violation, saying the service is responsible for itself, and fails to launch. Removing that constraint (or adding the service itself to the constraint) works fine. The service is an optional download, and installed to /Users/Shared with a LaunchAgent specifying the MachService. The service is correctly launched and seems to pass all codesigning, notarization, and other checks, but the Responsible isn't set to the "calling" app. Is this broken, or working as intended?
3
0
196
Nov ’25
How to force cancel a task that doesn't need cleanup and doesn't check for cancellation?
How can you force cancel a task that doesn't need cleanup and doesn't check for cancellation? If this cannot be done, would this be a useful addition to Swift? Here is the situation: The async method doesn't check for cancellation since it is not doing anything repetively (for example in a loop). For example, the method may be doing "try JSONDecoder().decode(Dictionary<String, ...>.self, from: data)" where data is a large amount. The method doesn't need cleanup. I would like the force cancellation to throw an error. I am already handling errors for the async method. My intended situation if that the user request the async method to get some JSON encoded data, but since it is taking longer that they are willing to wait, they would tap a cancellation button that the app provides.
1
0
93
May ’25
Crash on DispatchQueue.main.sync from isolated thread
I'm troubleshooting a crash I do not understand. I have a queue called DataQueue which never has anything dispatched to it - it's the sample buffer delegate of an AVCaptureVideoDataOutput. It can call DispatchQueue.main.sync to do some work on the main thread. It works fine no matter what we test, but has some crashes in the field that I need to fix. Here's it crashing: AppleCameraDataDelegate.dataQueue 0 libsystem_kernel.dylib 0x7bdc __ulock_wait + 8 1 libdispatch.dylib 0x4a80 _dlock_wait + 52 2 libdispatch.dylib 0x486c _dispatch_thread_event_wait_slow$VARIANT$mp + 52 3 libdispatch.dylib 0x113d8 __DISPATCH_WAIT_FOR_QUEUE__ + 332 4 libdispatch.dylib 0x10ff0 _dispatch_sync_f_slow + 140 The main thread isn't doing something I asked it to, but appears to be busy: Thread 0 libsystem_kernel.dylib 0x71a4 __psynch_cvwait + 8 1 libsystem_pthread.dylib 0x7fd8 _pthread_cond_wait$VARIANT$mp + 1232 2 grpc 0x2cb670 gpr_cv_wait + 131 (sync.cc:131) 3 grpc 0x119688 grpc_core::Executor::ThreadMain(void*) + 225 (executor.cc:225) 4 grpc 0x2e023c grpc_core::(anonymous namespace)::ThreadInternalsPosix::ThreadInternalsPosix(char const*, void (*)(void*), void*, bool*, grpc_core::Thread::Options const&)::'lambda'(void*)::__invoke(void*) + 146 (thd.cc:146) 5 libsystem_pthread.dylib 0x482c _pthread_start + 104 6 libsystem_pthread.dylib 0xcd8 thread_start + 8 Can anyone help me understand why this is a crash?
4
0
135
Sep ’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!
2
0
140
Apr ’25
BGContinuedProcessingTask launchHandler invocation
I'm trying to understand how the API works to perform a function that can continue running if the user closes the app. For a very simple example, consider a function that increments a number on screen every second, counting from 1 to 100, reaching completion at 100. The user can stay in the app for 100s watching it work to completion, or the user can close the app say after 2s and do other things while watching it work to completion in the Live Activity. To do this when the user taps a Start Counting button, you'd 1 Call BGTaskScheduler.shared.register(forTaskWithIdentifier:using:launchHandler:). Question 1: Do I understand correctly, all of the logic to perform this counting operation would exist entirely in the launchHandler block (noting you could call another function you define passing it the task to be able to update its progress)? I am confused because the documentation states "The system runs the block of code for the launch handler when it launches the app in the background." but the app is already open in the foreground. This made me think this block is not going to be invoked until the user closes the app to inform you it's okay to continue processing in the background, but how would you know where to pick up. I want to confirm my thinking was wrong, that all the logic should be in this block from start to completion of the operation, and it's fine even if the app stays in the foreground the whole time. 2 Then you'd create a BGContinuedProcessingTaskRequest and set request.strategy = .fail for this example because you need it to start immediately per the user's explicit tap on the Start Counting button. 3 Call BGTaskScheduler.shared.submit(request). Question 2: If the submit function throws an error, should you handle it by just performing the counting operation logic (call your function without passing a task)? I understand this can happen if for some reason the system couldn't immediately run it, like if there's already too many pending task requests. Seems you should not show an error message to the user, should still perform the request and just not support background continued processing for it (and perhaps consider showing a light warning "this operation can't be continued in the background so keep the app open"). Or should you still queue it up even though the user wants to start counting now? That leads to my next question Question 3: In what scenario would you not want the operation to start immediately (the queue behavior which is the default), given the app is already in the foreground and the user requested some operation? I'm struggling to think of an example, like a button titled Compress Photos Whenever You Can, and it may start immediately or maybe it won't? While waiting for the launchHandler to be invoked, should the UI just show 0% progress or "Pending" until the system can get to this task in the queue? Struggling to understand the use cases here, why make the user wait to start processing when they might not even intend to close the app during the operation? Thanks for any insights! As an aside, a sample project with a couple use cases would have been incredibly helpful to understand how the API is expected to be used.
8
0
292
Oct ’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]).
10
0
270
Sep ’25
iOS BGTaskScheduler
Hi! I'm trying to submit a task request into BGTaskScheduler when I background my app. The backgrounding triggers an update of data to a shared app groups container. I'm currently getting the following error and unsure where it's coming from: *** Assertion failure in -[BGTaskScheduler _unsafe_submitTaskRequest:error:], BGTaskScheduler.m:274 Here is my code: BGAppRefreshTaskRequest *request = [[BGAppRefreshTaskRequest alloc] initWithIdentifier:kRBBackgroundTaskIdentifier]; NSError *error = nil; bool success = [[BGTaskScheduler sharedScheduler] submitTaskRequest:request error:&error];
7
0
150
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.
2
0
133
Apr ’25
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?
3
0
3.0k
Jun ’25
Launch constraints using LightweightCodeRequirements framework
MacOS Version: 14.7.2 macOS SDKs: macOS 14.5 -sdk macosx14.5 I am working on a sample program for validation Against: Team Identifier Developer ID I started with validating Team Identifier, but my validation is not working and it is allowing to launch programs which are not matching the team identifier in the signature. Below is my code: func verifyExecutableWithLCR(executablePath: String, arguments: [String]) -&gt; Bool { let task = Process() task.launchPath = executablePath task.arguments = arguments if #available(macOS 14.4, *) { print("launchRequirementData is available on this system.") do { let req = try OnDiskCodeRequirement.allOf { TeamIdentifier("ABCDEFGHI") //SigningIdentifier("com.***.client.***-Client.****") } let encoder = PropertyListEncoder() encoder.outputFormat = .xml let requirementData = try encoder.encode(req) task.launchRequirementData = requirementData print("launchRequirementData is set.") try task.run() print("[SUCCESS] Executable passed the code signature verification.") return true } catch { print("[ERROR] Code signature verification failed: \(error.localizedDescription)") return false } } else { print("[WARNING] launchRequirement is not available on this macOS version.") return false } } Could you please help me in identifying whay am I doing wrong here?
7
0
556
Feb ’25