Quiz 6 question 2 solution

let dictLock = DispatchSemaphore(value: 1)
var originSemaphores: [String: DispatchSemaphore] = [:]

// make a non blocking HTTP request
func makeHttpRequest(url: String, origin: String, complete: @escaping (() -> Void)) {
    dictLock.wait()
    if originSemaphores[origin] == nil {
        originSemaphores[origin] = DispatchSemaphore(value: 2)
    }
    let semaphore = originSemaphores[origin]!
    dictLock.signal()
    
    DispatchQueue.global(qos: .default).async {
        semaphore.wait()
        blockingNetworkRequest(url: url)
        complete()
        semaphore.signal()
    }
}