## Function: SB-THREAD:MUTEX-OWNER
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> Current owner of the mutex, NIL if the mutex is free. Naturally,
> this is racy by design (another thread may acquire the mutex after
> this function returns), it is intended for informative purposes. For
> testing whether the current thread is holding a mutex see
> HOLDING-MUTEX-P.

### Lambda list
```cl
(sb-thread:mutex)
```