semaphore deadlock with dispathc_async

test.swift

func waitFunc(completion:(Bool) -> Void ) {
        dispatch_async(dispatch_get_main_queue()) {
            print("1")
            sleep(1)
            completion(true)
        }
    }
    func Test() {
        for i in 0..<5 {
            print("another")
            let semaphore = dispatch_semaphore_create(0)
            waitFunc() { finished in
                print("FINISHED = \(finished)")
                dispatch_semaphore_signal(semaphore)
            }
            dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER)
        }
    }