https://priteshrnandgaonkar.github.io/concurrency-with-swift-3/
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import UIKit class ViewController: UIViewController { var button : UIButton? = nil func action(selector:UIButton) { print("Button Clicked") } override func viewDidLoad() { print("--viewDidLoad--") super.viewDidLoad() self.button = UIButton(type: UIButtonType.roundedRect) as UIButton self.button?.backgroundColor = UIColor.orange self.button?.addTarget(self, action: #selector(action), for: UIControlEvents.touchUpInside) self.button?.frame = CGRect(x: 80, y: 60, width: 200, height: 80) self.button?.setTitle("Push Me", for: .normal) print("button created") self.view.addSubview(self.button!) print("view hieararchy added button") } override func viewDidAppear(_ animated: Bool) { super.viewDidAppear(animated) let dispatchQueue = DispatchQueue(label: "com.prit.TestGCD.DispatchQueue", attributes: .concurrent) let semaphore = DispatchSemaphore(value: 2) dispatchQueue.async { ／／At this point the readers are not locking the resource. ／／They are only locking the entry section so no other reader can enter it while they are in it. if semaphore.wait(timeout: .distantFuture) == .success { print("success adding block 1") } else { print("timed out") } ／／Once the first reader is in the entry section, it will lock the resource. Doing this will prevent any writers from accessing it print("enter critical section") Thread.sleep(forTimeInterval: 5) print("exit critical section") ／／Once the reader is done executing the entry section, it will unlock it by signaling the mutex semaphore.signal() } dispatchQueue.async { if semaphore.wait(timeout: .distantFuture) == .success { print("success adding block 2") } else { print("timed out") } print("Sema block 2 sleep for 2 sec") Thread.sleep(forTimeInterval: 2) print("Sema block 2 signal") semaphore.signal() } dispatchQueue.async { if semaphore.wait(timeout: .distantFuture) == .success { print("success for adding block 3") } else { print("timed out") } print("Sema block 3 signal") semaphore.signal() } dispatchQueue.async { if semaphore.wait(timeout: .distantFuture) == .success { print("success for adding block 4") } else { print("timed out") } print("Sema block 4 signal") semaphore.signal() } } override func didReceiveMemoryWarning() { super.didReceiveMemoryWarning() // Dispose of any resources that can be recreated. } } |