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KERN_NOT_SUPPORTED
Not a generic feature-unsupported status
KERN_NOT_SUPPORTED has a specific historical meaning in XNU kern_return.h: the operation targeted an empty thread activation with no linked thread. It should not be read as a broad statement that macOS, a device, or an API feature does not support the requested capability.
The right diagnosis is an object-state check. Identify whether the caller retained a thread-activation reference after it lost its thread, or passed an activation object to an API that requires a linked, live thread.
What to inspect
- Determine what created the activation and when a thread was associated with it.
- Check whether thread termination or task teardown detached the underlying thread first.
- Determine whether legacy Mach code can use a modern supported abstraction instead.
- Look for a more precise lifetime result from the surrounding API after the activation becomes invalid.
References
- Apple XNU: kern_return.h
- Apple Kernel Programming Guide: tasks and threads
- Apple Kernel Programming Guide: kernel thread APIs
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