fetchData function for medium blog post about DispatchGroup and DispatchSemaphore, https://link.medium.com/zJMQPUHaeZ

main.swift

func combineAsyncCallsWithSemaphore(completionHandler: @escaping (String)->()) {
    let semaphore = DispatchSemaphore(value: 0)
    var text = ""
    
    DispatchQueue.global().async {
        fetchData(0, delay: 0.4) {
            text += $0
            semaphore.signal()
        }
        semaphore.wait() // wait for the first fetchData complete
        
        fetchData(1, delay: 0.2) {
            text += $0
            semaphore.signal()
        }
        semaphore.wait() // wait for the second fetchData complete
        
        completionHandler(text)
    }
}

combineAsyncCallsWithSemaphore() {
    print($0)
    exit(0)
}

RunLoop.current.run()