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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About GCD (Grand Central Dispatch) in an extension.
We are currently developing a VoIP application that supports Local Push extention. I would like to ask for your advice on how the extension works when the iPhone goes into sleep mode. Our App are using GCD (Grand Central Dispatch) to perform periodic processing within the extension, creating a cycle by it. [sample of an our source] class LocalPushProvider: NEAppPushProvider { let activeQueue: DispatchQueue = DispatchQueue(label: "com.myapp.LocalPushProvider.ActiveQueue", autoreleaseFrequency: .workItem) var activeSchecule: Cancellable? override func start(completionHandler: @escaping (Error?) -> Void) { : self.activeSchecule = self.activeQueue.schedule( after: .init(.now() + .seconds(10)), // start schedule after 10sec interval: .seconds(10) // interval 10sec ) { self.activeTimerProc() } completionHandler(nil) } } However In this App that we are confirming that when the iPhone goes into sleep mode, self.activeTimerProc() is not called at 10-second intervals, but is significantly delayed (approximately 30 to 180 seconds). What factors could be causing the timer processing using GCD not to be executed at the specified interval when the iPhone is in sleep mode? Also, please let us know if there are any implementation errors or points to note. I apologize for bothering you during your busy schedule, but I would appreciate your response.
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Jun ’25
Processes & Concurrency Resources
General: DevForums subtopic: App & System Services > Processes & Concurrency Processes & concurrency covers a number of different technologies: Background Tasks Resources Concurrency Resources — This includes Swift concurrency. Service Management Resources XPC Resources Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com"
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Jul ’25
Background service on MacOS
Hi, I'm working on an application on MacOS. It contains a port-forward feature on TCP protocol. This application has no UI, but a local HTTP server where user can access to configure this application. I found that my application always exit for unknown purpose after running in backgruond for minutes. I think this is about MacOS's background process controlling. Source codes and PKG installers are here: https://github.com/burningtnt/Terracotta/actions/runs/16494390417
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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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Aug ’25
How can I get a Subscriber to subscribe to get only 4 elements from an array?
Hello, I am trying to implement a subscriber which specifies its own demand for how many elements it wants to receive from a publisher. My code is below: import Combine var array = [1, 2, 3, 4, 5, 6, 7] struct ArraySubscriber<T>: Subscriber { typealias Input = T typealias Failure = Never let combineIdentifier = CombineIdentifier() func receive(subscription: any Subscription) { subscription.request(.max(4)) } func receive(_ input: T) -> Subscribers.Demand { print("input,", input) return .max(4) } func receive(completion: Subscribers.Completion<Never>) { switch completion { case .finished: print("publisher finished normally") case .failure(let failure): print("publisher failed due to, ", failure) } } } let subscriber = ArraySubscriber<Int>() array.publisher.subscribe(subscriber) According to Apple's documentation, I specify the demand inside the receive(subscription: any Subscription) method, see link. But when I run this code I get the following output: input, 1 input, 2 input, 3 input, 4 input, 5 input, 6 input, 7 publisher finished normally Instead, I expect the subscriber to only "receive" elements 1, 2, 3, 4 from the array. How can I accomplish this?
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Aug ’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.
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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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Mac: Best way to distinguish native app process and script process spawned from executable (e.g. python node) through process_id
I'm working on a Mac app that receives a process ID via NSXPCConnection, and I'm trying to figure out the best way to determine whether that process is a native macOS app like Safari—with bundles and all—or just a script launched by something like Node or Python. The executable is signed with a Team ID using codesign. I was thinking about getting the executable's path as one way to handle it, but I’m wondering if there’s a more reliable method than relying on the folder structure.
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BGContinuedProcessingTask Notification Error
Hello im creating an expo module using this new API, but the problem i found currently testing this functionality is that when the task fails, the notification error doesn't go away and is always showing the failed task notification even if i start a new task and complete that one. I want to implement this module into the production app but i feel like having always the notification error might confuse our users or find it a bit bothersome. Is there a way for the users to remove this notification? Best regards!
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Privileged helper without SMJobBless
To establish a privileged helper daemon from a command line app to handle actions requiring root privileges I still use the old way of SMJobBless. But this is deprecated since OSX 10.13 and I want to finally update it to the new way using SMAppService. As I'm concerned with securing it against malicious exploits, do you have a recommended up-to-date implementation in Objective-C establishing a privileged helper and verifying it is only used by my signed app? I've seen the suggestion in the documentation to use SMAppService, but couldn't find a good implementation covering security aspects. My old implementation in brief is as follows: bool runJobBless () { // check if already installed NSFileManager* filemgr = [NSFileManager defaultManager]; if ([filemgr fileExistsAtPath:@"/Library/PrivilegedHelperTools/com.company.Helper"] && [filemgr fileExistsAtPath:@"/Library/LaunchDaemons/com.company.Helper.plist"]) { // check helper version to match the client // ... return true; } // create authorization reference AuthorizationRef authRef; OSStatus status = AuthorizationCreate (NULL, kAuthorizationEmptyEnvironment, kAuthorizationFlagDefaults, &authRef); if (status != errAuthorizationSuccess) return false; // obtain rights to install privileged helper AuthorizationItem authItem = { kSMRightBlessPrivilegedHelper, 0, NULL, 0 }; AuthorizationRights authRights = { 1, &authItem }; AuthorizationFlags flags = kAuthorizationFlagDefaults | kAuthorizationFlagInteractionAllowed | kAuthorizationFlagPreAuthorize | kAuthorizationFlagExtendRights; status = AuthorizationCopyRights (authRef, &authRights, kAuthorizationEmptyEnvironment, flags, NULL); if (status != errAuthorizationSuccess) return false; // SMJobBless does it all: verify helper against app and vice-versa, place and load embedded launchd.plist in /Library/LaunchDaemons, place executable in /Library/PrivilegedHelperTools CFErrorRef cfError; if (!SMJobBless (kSMDomainSystemLaunchd, (CFStringRef)@"com.company.Helper", authRef, &cfError)) { // check helper version to match the client // ... return true; } else { CFBridgingRelease (cfError); return false; } } void connectToHelper () { // connect to helper via XPC NSXPCConnection* c = [[NSXPCConnection alloc] initWithMachServiceName:@"com.company.Helper.mach" options:NSXPCConnectionPrivileged]; c.remoteObjectInterface = [NSXPCInterface interfaceWithProtocol:@protocol (SilentInstallHelperProtocol)]; [c resume]; // call function on helper and wait for completion dispatch_semaphore_t semaphore = dispatch_semaphore_create (0); [[c remoteObjectProxy] callFunction:^() { dispatch_semaphore_signal (semaphore); }]; dispatch_semaphore_wait (semaphore, dispatch_time (DISPATCH_TIME_NOW, 10 * NSEC_PER_SEC)); dispatch_release (semaphore); [c invalidate]; [c release]; }
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Did GCD change in macOS 26
Some users of my Mac app are complaining of redrawing delays. Based on what I see in logs, my GCD timer event handlers are not being run in a timely manner although the runloop is still pumping events: sometimes 500ms pass before a 15ms timer runs. During this time, many keypresses are routed through -[NSApplication sendEvent:], which is how I know it's not locked up in synchronous code. This issue has not been reported in older versions of macOS. I start the timer like this: _gcdUpdateTimer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue()); dispatch_source_set_timer(_gcdUpdateTimer, dispatch_time(DISPATCH_TIME_NOW, period * NSEC_PER_SEC), period * NSEC_PER_SEC, 0.0005 * NSEC_PER_SEC); dispatch_source_set_event_handler(_gcdUpdateTimer, ^{ …redraw… });
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