macOS kernel return 40 (KERN_LOCK_OWNED): meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: The requested Mach lock is currently owned by another thread.

Could be also:
Constant	Type	OS
ippStsWrongIntersectVOI	Intel Ipp Status	Any
ELOOP	errno	Linux
EMSGSIZE	errno	Mac
EL3RST	errno	Solaris
ENOSYS	errno	Windows
CORRUPT_ACCESS_TOKEN	BugCheck Code	Windows

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KERN_LOCK_UNSTABLE	KERN_LOCK_OWNED_SELF

KERN_LOCK_OWNED

Contention on a valid lock

KERN_LOCK_OWNED means that another thread owns the lock at the time of the request. Unlike KERN_LOCK_UNSTABLE, the reported owner has not disappeared; unlike KERN_LOCK_OWNED_SELF, the caller is not attempting a conflicting operation on its own lock.

The return value is a concurrency observation, not proof of a deadlock. Its significance depends on the expected critical-section duration and on whether the API provides waiting, try-lock, or explicit scheduling behavior.

What to inspect

Identify the owning thread and the work it is performing.
Measure the normal critical-section duration under comparable load.
Defer work or use the API waiting mechanism rather than polling if the contract allows it.
Check persistent ownership for a cycle with another lock or blocked operation.

References

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