## Function: SB-THREAD:WAIT-ON-SEMAPHORE
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> Decrement the count of SEMAPHORE by N if the count would not be negative.
> 
> Else blocks until the semaphore can be decremented. Returns the new count of
> SEMAPHORE on success.
> 
> If TIMEOUT is given, it is the maximum number of seconds to wait. If the count
> cannot be decremented in that time, returns NIL without decrementing the
> count.
> 
> If NOTIFICATION is given, it must be a SEMAPHORE-NOTIFICATION object whose
> SEMAPHORE-NOTIFICATION-STATUS is NIL. If WAIT-ON-SEMAPHORE succeeds and
> decrements the count, the status is set to T.

### Lambda list
```cl
(sb-thread:semaphore &key sb-thread::n sb-thread::timeout sb-thread::notification)
```