Semaphore Multithreaded Shared Resource

var sharedResource = [String]()

let semaphore = DispatchSemaphore(value: 0)

let dispatchQueue = DispatchQueue.global(qos: .background)
dispatchQueue.async {
    self.fetchImage { (_, _) in 
       print("Finished fetching image 1")
       self.sharedResoure.append("1")
       semaphore.signal()
    }
    semaphore.wait()

    self.fetchImage { (_, _) in 
       print("Finished fetching image 2")
       self.sharedResoure.append("1")
       semaphore.signal()
    }
    semaphore.wait()

    self.fetchImage { (_, _) in 
       print("Finished fetching image 3")
       self.sharedResoure.append("1")
       semaphore.signal()
    }
    semaphore.wait()

    print("Start fetching images")
}

result:
Start fetching images
Finished fetching image 1
Finished fetching image 2
Finished fetching image 3