semaphore.swift

import Foundation

func testFunction(completion: () -> ()) {
    dispatch_async(dispatch_get_main_queue()) {
        completion()
    }
}

func testSemaphore() {
    let semaphore = dispatch_semaphore_create(0)
    
    testFunction {
        dispatch_semaphore_signal(semaphore)
    }
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER)
}

print("1")

testSemaphore()

print("2")