ios - What is swift's equivalent of a Pthread semaphore or a spin lock? -

background

i using objc_sync_enter/exit pairs manage locks:

func sync(lock: anyobject, closure: () -> ()) {     objc_sync_enter(lock)     closure()     objc_sync_exit(lock) }  func sync<t>(lock: anyobject, closure: () -> t ) -> t {     var t : t     objc_sync_enter(lock)     t = closure()     objc_sync_exit(lock)     return t } 

i can use these mechanisms update semaphore count down tasks need complete.

now, in separate thread, wait until semaphore reaches zero, perhaps using pthread semaphore or kind of cheap/light spin lock?

var semaphore = 2  // ->0 using sync() when preparation complete fun call_me_when_semaphore_becomes_zero() { }  

question

how can wait boolean condition using swift/ios synchronization mechanisms?

it nice if interface looked this:

// implementation func sync_wait(lock: anyobject, condition: (()->bool), closure: (() -> ())) {     // need here -------------------------------------------------------     // using lock, wait until condition becomes true, , call closure     // ---------------------------------------------------------------------- }  // call sync_wait( semaphore, condition: { semaphore==0 }, closure: { call_me_when_semaphore_becomes_zero() } )