## Function: SB-THREAD:TRY-SEMAPHORE
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> Try to decrement the count of SEMAPHORE by N. If the count were to
> become negative, punt and return NIL, otherwise return the new count of
> SEMAPHORE.
> 
> If NOTIFICATION is given it must be a semaphore notification object
> with SEMAPHORE-NOTIFICATION-STATUS of NIL. If the count is decremented,
> the status is set to T.

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