macOS kernel return 30 (KERN_ALREADY

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: A thread attempted to register another wait for an event while it was already waiting for that event.

Could be also:
Constant	Type	OS
ERROR_READ_FAULT	Win32 error	Windows
ippStsWrongIntersectQuad	Intel Ipp Status	Any
EROFS	errno	Any
KMODE_EXCEPTION_NOT_HANDLED	BugCheck Code	Windows

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KERN_INVALID_OBJECT	KERN_DEFAULT_SET

KERN_ALREADY_WAITING

A duplicated wait-state transition

KERN_ALREADY_WAITING identifies a wait-state invariant violation: a thread tried to wait for an event for which it already had a wait registered. This is not equivalent to lock contention or a slow semaphore; it says the state machine has attempted to enter the waiting state twice.

The valuable evidence is the first wait registration. A later call often exposes a missing wakeup, cleanup path, cancellation path, or an incorrectly reused thread/event association.

What to inspect

Trace the event identifier, thread identity, and call stacks for both wait attempts.
Follow every path that removes, wakes, cancels, or reuses the wait registration.
Check whether a callback can re-enter the same wait logic before the first wait completes.
Check whether an error path skipped the transition that makes the thread eligible to wait again.

References

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