What is ZTUM?

Hi! I recently encountered a crash:

OS Version: tvOS 14.5
Report Version: 104

Exception Type: Unknown (SIGSEGV)
Exception Codes: SEGV_ACCERR at 0x0000000000000040
Crashed Thread: 9

Application Specific Information:

Thread 9 Crashed:
0   libswift_Concurrency.dylib      0x10127d5a4         swift::TaskGroup::offer
1   libswift_Concurrency.dylib      0x10127adb0         swift::AsyncTask::completeFuture
2   libswift_Concurrency.dylib      0x10127bec4         swift_continuation_await
3   libswift_Concurrency.dylib      0x101278bfc         swift::runJobInEstablishedExecutorContext

Had no luck finding explanations for what "ZTUM" means in general (searched the internet, scanned related binaries, searched the Swift repo), much less what it means when coinciding with TaskGroup. Thus,

  • What does ZTUM mean?
  • How can I approach debugging crashes in Concurrency.TaskGroup like the one in the stack trace?


Can't say what ZTUM means but this crash looks like a known issue on the back deployed concurrency runtime. You may be able to workaround it by changing the structure of your interaction with TaskGroup but I haven't seen any particular solution.


@hakonk This is the following bug: TaskGroup-Related Crash. You can remove your use of TaskGroup, or live with it for now — it’s fixed as of iOS 15.4.

Thanks for replying @Jon_Shier and @danhalliday. Since the crash happened on a back deployed version of swift_Concurrency.dylib, I guess the issue stems from Xcode 13.4.1 not bundling a version of the dylib containing the fix that was deployed to iOS/tvOS >= 15.4. Is this assumption correct, and if so, will the next Xcode toolchain make sure the fix gets included when back deploying?