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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ExtensionKit & ExtensionFoundation process lifecycle
An XPC service’s process has a system-managed lifecycle: the process is launched on-demand when another process tries to connect to it, and the system can decide to kill it when system resources are low. XPC services can tell the system when they shouldn’t be killed using xpc_transaction_begin/end. Do extensions created with ExtensionFoundation and/or ExtensionKit have the same behavior?
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169
Jul ’25
Need to start the Mac application automatically
I am developing the application in Mac. My requirement is to start the application automatically when user login. I have tried adding the plist file in launch agents, But it doesn't achieve my requirement. Please find the code added in the launch agents <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>Label</key> <string>com.sftk.secure</string> <key>ProgramArguments</key> <array> <string>/Applications/Testing.app/Contents/MacOS/Testing</string> </array> <key>RunAtLoad</key> <true/> <key>KeepAlive</key> <false/> </dict> </plist> I have tried by adding manually in the setting, but it was opened sometimes and closed suddenly. On open manually it works. Please provide a solution to start the application automatically on system starts
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136
Jul ’25
iOS Team Provisioning Profile” Missing UIBackgroundModes Entitlement
I’m trying to enable Background Modes (specifically for audio, background fetch, remote notifications) in my iOS SwiftUI app, but I’m getting this error: Provisioning profile “iOS Team Provisioning Profile: [my app]” doesn’t include the UIBackgroundModes entitlement. On the developer website when I make the provision profile It doesnt give me the option to allow background modes. I added it to the sign in capabilities seccion in X code and matched the bundle ID to the provision profile and certificate etc but it still runs this error because the provision profile doesnt have the entitlements..
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297
Jul ’25
Crash iOS 26 Beta
We are experiencing a crash in our application that only occurs on devices running iOS beta 26. It looks like a Beta problem. The crash appears to be caused by an excessive number of open File Descriptors. We identified this after noticing a series of crashes in different parts of the code each time the app was launched. Sometimes it would crash right at the beginning, when trying to load the Firebase plist file. That’s when we noticed a log message saying “too many open files,” and upon further investigation, we found that an excessive number of File Descriptors were open in our app, right after the didFinishLaunching method of the AppDelegate. We used the native Darwin library to log information about the FDs and collected the following: func logFDs() { var rlim = rlimit() if getrlimit(RLIMIT_NOFILE, &rlim) == 0 { print("FD LIMIT: soft: \(rlim.rlim_cur), hard: \(rlim.rlim_max)") } // Count open FDs before Firebase let openFDsBefore = countOpenFileDescriptors() print("Open file descriptors BEFORE Firebase.configure(): \(openFDsBefore)") } private func countOpenFileDescriptors() -> Int { var count = 0 let maxFD = getdtablesize() for fd in 0..<maxFD { if fcntl(fd, F_GETFD) != -1 { count += 1 } } return count } With this code, we obtained the following data: On a device with iOS 26 Beta 1, 2, or 3: FD LIMIT: soft: 256, hard: 9223372036854775807 Open file descriptors BEFORE Firebase.configure(): 256 On a device with iOS 18: FD LIMIT: soft: 256, hard: 9223372036854775807 Open file descriptors BEFORE Firebase.configure(): 57 In the case of the device running iOS 26 beta, the app crashes when executing Firebase.configure() because it cannot open the plist file, even though it can be found at the correct path — meaning the OS locates it. To confirm this was indeed the issue, we used the following code to close FDs before proceeding with Firebase configuration. By placing a breakpoint just before Firebase.configure() and running the following LLDB command: expr -l c -- for (int fd = 180; fd < 256; fd++) { (int)close(fd); } This released the FDs, allowing Firebase to proceed with its configuration as expected. However, the app would later crash again after hitting the soft limit of file descriptors once more. Digging deeper, we used this code to try to identify which FDs were being opened and causing the soft limit to be exceeded: func checkFDPath() { var r = rlimit() if getrlimit(RLIMIT_NOFILE, &r) == 0 { print("FD LIMIT: soft: \(r.rlim_cur), hard: \(r.rlim_max)") for fd in 0..<Int32(r.rlim_cur) { var path = [CChar](repeating: 0, count: Int(PATH_MAX)) if fcntl(fd, F_GETPATH, &path) != -1 { print(String(cString: path)) } } } } We ran this command at the very beginning of the didFinishLaunching method in the AppDelegate. On iOS 26, the log repeatedly showed Cryptexes creating a massive number of FDs, such as: /dev/null /dev/ttys000 /dev/ttys000 /private/var/mobile/Containers/Data/Application/AEE414F2-7D6F-44DF-A6D9-92EDD1D2B014/Library/Application Support/DTX_8.191.1.1003.sqlite /private/var/mobile/Containers/Data/Application/AEE414F2-7D6F-44DF-A6D9-92EDD1D2B014/Library/Caches/KSCrash/MyAppScheme/Data/ConsoleLog.txt /private/var/mobile/Containers/Data/Application/AEE414F2-7D6F-44DF-A6D9-92EDD1D2B014/Library/HTTPStorages/mybundleId/httpstorages.sqlite /private/var/mobile/Containers/Data/Application/AEE414F2-7D6F-44DF-A6D9-92EDD1D2B014/Library/HTTPStorages/mybundleId/httpstorages.sqlite-wal /private/var/mobile/Containers/Data/Application/AEE414F2-7D6F-44DF-A6D9-92EDD1D2B014/Library/HTTPStorages/mybundleId/httpstorages.sqlite-shm /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.01 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.11 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.12 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.13 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.14 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.15 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.16 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.17 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.18 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.19 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.20 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.21 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.22 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.23 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.24 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.25 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.26 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.29 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.30 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.31 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.32 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.36 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.37 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.38 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.39 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.40 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e … This repeats itself a lot of times. … /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.36 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.37 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.38 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.39 /private/preboot/Cryptexes/OS/System/Library/Caches/com.apple.dyld/dyld_shared_cache_arm64e.40
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Jul ’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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196
Jul ’25
Running external binaries from Swift Package (TTS engine): Operation not permitted from Xcode app
Hi everyone, We’re developing a macOS SwiftUI app that uses a local Swift Package (CasSherpaCore) to invoke an external compiled binary (sherpa-onnx-offline-tts) for text-to-speech synthesis using system calls. The package works flawlessly when tested from terminal or via a lightweight test C program. However, when we invoke it from a SwiftUI app (even with Full Disk Access granted to Xcode and Terminal), we consistently get the error: sh: /Users/xxxxxxxxxxx/SherpaONNX/sherpa-onnx/build/bin/sherpa-onnx-offline-tts: Operation not permitted We’ve tried: Granting Full Disk Access to Xcode and Terminal. Removing the quarantine flag with xattr -d com.apple.quarantine. Setting executable permission via chmod +x. Using both system() and Process in C and Swift contexts. Testing within a Swift Package that’s integrated into the app as a local dependency. Running the command manually from terminal (works perfectly). It appears that macOS (or Xcode’s runtime sandbox) is restricting execution of binaries from certain locations or contexts when launched via system() inside the app. Questions: Is there a specific entitlement or configuration that allows execution of local binaries from a SwiftUI macOS app? Is this related to System Integrity Protection (SIP) or a hardened runtime limitation? Are there best practices or alternative approaches to safely execute local TTS binaries from within a Swift app? Any help would be deeply appreciated. This is a core feature in our project and we’re stuck at this point. Thank you so much in advance!
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90
Jul ’25
When using SMAppService to register a daemon, is it possible to let the authorization dialog show on behalf of my application? e.g.: showing the app name, custom icon and prompt, etc..
My app is for personal use currently, so distribution won't be a problem. It registers a privileged helper using SMAppService, and I was wondering whether there is a way to customize the authorization dialog that the system presents to the user.
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138
Jul ’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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Jul ’25
SMAppService daemon not running
My app uses SMAppService to register a privileged helper, the helper registers without errors, and can be seen in System Settings. I can get a connection to the service and a remote object proxy, but the helper process cannot be found in Activity Monitor and the calls to the proxy functions seem to always fail without showing any specific errors. What could be causing this situation?
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250
Jul ’25
Does BGAppRefreshTask require an internet connection?
Basically the title. I am trying to implement a local notification to trigger, regardless of internet connection, around 3-5pm if a certain array in the app is not empty to get the user to sync unsaved work with the cloud. I wanted to used the BGAppRefreshTask as I saw it was lightweight and quick for just posting a banner notification but after inspecting it in the console, it looks like it needs internet connection to trigger. Is this the case or am I doing something wrong? Should I be using the BGProcessingTask instead?
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95
Jul ’25
can an xpc service access the keychain.
I am trying to create an app bundle with an xpc service. The main app creates a keychain item, and attempts to share (keychain access groups) with the xpc service it includes in its bundle. However, the xpc service always encounters a 'user interaction not allowed' error regardless of how I create the keychain item. kSecAttrAccessiblei is set to kSecAttrAccessibleWhenUnlockedThisDeviceOnly, the keychain access group is set for both the main app and the xpc service and in the provisioning profile. I've tried signing and notarizing. Is it ever possible for an xpc service to access the keychain? This all on macos 15.5.
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Jul ’25
Alternatives to com.apple.security.temporary-exception.apple-events: com.apple.Terminal ?
Hello 👋 Our team added com.apple.security.temporary-exception.apple-events: com.apple.Terminal recently to our Mac app to be able to tell the terminal to execute a specific command line automatically for the user when clicking a button but we've been rejected during review because of this entitlement so for now we've deleted it and deleted the associated feature. It concerns the following feature (see attachment). Context: Among other things the application enable to review pull request changes (remote) and we would like a button to automatically clone the pull request on disk when user click a button. We would like to use terminal for security reason as when cloning using git command we need ssh keys or other credential and there's no reason (rather than technical ones) that the user provide us such private information that is stored in the ~/.ssh. We prefer think the other way around and tell the user what to execute instead (no credentials involved or shared). We referred to: https://developer.apple.com/library/archive/documentation/Miscellaneous/Reference/EntitlementKeyReference/Chapters/AppSandboxTemporaryExceptionEntitlements.html I admit it's unclear for me if this will imply a 100% rejection or if these entitlements are deprecated. Is "com.apple.security.temporary-exception.apple-events: com.apple.Terminal" an entitlement that is reserved for special Apple partners ? Is it an entitlement that we should demonstrate usage first ? Or should we completely remove the feature if we distribute through the App Store ? Is Apple advice for other APIs to develop such features (execute command line for the user) when distributing through the App Store ? As said we've disabled the feature for now. Thank you in advance for those who will take time to answer this,
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147
Jul ’25
System Network Extension XPC with LaunchAgent
I've discovered that a system network extension can communicate with a LaunchDaemon (loaded using SMAppService) over XPC, provided that the XPC service name begins with the team ID. If I move the launchd daemon plist to Contents/Library/LaunchAgents and swap the SMAppService.daemon calls to SMAppService.agent calls, and remove the .privileged option to NSXPCConnection, the system extension receives "Couldn't communicate with a helper application" as an error when trying to reach the LaunchAgent advertised service. Is this limitation by design? I imagine it is, but wanted to check before I spent any more time on it.
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221
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
Reliable 30-minute background data fetching for safety-critical monitoring app?
I'm developing a safety-critical monitoring app that needs to fetch data from government APIs every 30 minutes and trigger emergency audio alerts for threshold violations. The app must work reliably in background since users depend on it for safety alerts even while sleeping. Main Challenge: iOS background limitations seem to prevent consistent 30-minute intervals. Standard BGTaskScheduler and timers get suspended after a few minutes in background. Question: What's the most reliable approach to ensure consistent 30-minute background monitoring for a safety-critical app where missed alerts could have serious consequences? Are there special entitlements or frameworks for emergency/safety applications? The app needs to function like an alarm clock - working reliably even when backgrounded with emergency audio override capabilities.
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548
Jul ’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
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127
Jul ’25
Expected behavior from apps when MacOS goes to sleep
Every time macOS goes to sleep the processes get suspended which is expected. But during the sleep period, all processes keep coming back and they all get a small execution window where they make some n/w requests. Regardless of what power settings i have. It also does not matter whether my app is a daemon or not Is there any way that i can disable this so that when system is in sleep, it stays in suspended, no intermittent execution window? I have tried disabling Wake for network access setting but processes still keep getting intermittent execution window. Is there any way that i can prevent my app from coming back while in sleep. I don't want my app to get execution window, perform some executions and then get suspended not knowing when it will get execution window again?
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117
Aug ’25
How to correctly deploy bundled launchdaemons/launchagents?
I'm working on an enterprise product that's mainly a daemon (with Endpoint Security) without any GUI component. I'm looking into the update process for daemons/agents that was introduced with Ventura (Link), but I have to say that the entire process is just deeply unfun. Really can't stress this enough how unfun. Anyway... The product bundle now contains a dedicated Swift executable that calls SMAppService.register for both the daemon and agent. It registers the app in the system preferences login items menu, but I also get an error. Error registering daemon: Error Domain=SMAppServiceErrorDomain Code=1 "Operation not permitted" UserInfo={NSLocalizedFailureReason=Operation not permitted} What could be the reason? I wouldn't need to activate the items, I just need them to be added to the list, so that I can control them via launchctl. Which leads me to my next question, how can I control bundled daemons/agents via launchctl? I tried to use launchctl enable and bootstrap, just like I do with daemons under /Library/LaunchDaemons, but all I get is sudo launchctl enable system/com.identifier.daemon sudo launchctl bootstrap /Path/to/daemon/launchdplist/inside/bundle/Library/LaunchDaemons/com.blub.plist Bootstrap failed: 5: Input/output error (not super helpful error message) I'm really frustrated by the complexity of this process and all of its pitfalls.
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863
Aug ’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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153
Aug ’25