在 swift 3 中使用 NotificationCenter 停止 Dispatchqueue

Question

I have some task which I want to do asynchronously. So I am creating dispatchqueue in one class and doing some task.

//Adding Observer      
NotificationCenter.default.addObserver(forName: NSNotification.Name(rawValue: "NotificationIdentifier"), object: nil, queue: nil, using:catchNotification).

.

//Creating Background Thread.
     let anotherQueue = DispatchQueue(label: "Thread1", qos: .background)

    //Asynch thread.
    anotherQueue.async {
        for i in 0..<50 {
       print("\n 🔴",i)
            sleep(1)
        }
    }

but upon some events I want to stop this, and am handling something like this.

func catchNotification (notification:Notification) -> Void {
    //Stop the queue.
    anotherQueue.suspend()
}

Am posting notification some other class. notification is getting received. but thread is not getting suspended.

Here is the complete class if you want to refer.

LoginPresenter.swift

let anotherQueue = DispatchQueue(label: "Thread1", qos: .background)
class LoginPresenter : LoginInteractor {
func catchNotification (notification:Notification) -> Void {
    //Stop the queue.
    anotherQueue.suspend()
}

func LoginSuccessFull()
{   
    NotificationCenter.default.addObserver(forName: NSNotification.Name(rawValue: "NotificationIdentifier"), object: nil, queue: nil, using:catchNotification)

    //Asynch thread.
    anotherQueue.async {
        //Synch
        for i in 0..<50 {
       print("\n 🔴",i)
            sleep(1)
        }
    }
}

or is any other better method or mechanism is there to do this ?

Answer 1

Reading Apple`s GCD documentation , you could see the following:

The suspension occurs after completion of any blocks running at the time of the call.

This means that, every block will be executed, what has already been started. Just create a second block in your LoginSuccessFull function like:

anotherQueue.async {
  print("this is the second block")
}

If you suspend straight after the function call, this block will not be executed.

If you would like to cancel immediately the operations in GCD , you will have to write you own implementation. But to how , it is always the one question for GCD , because it is just not designed that way.

The other option would be to use NSOperationQueue , but there you have implement right the cancel logic for your NSOperation subclasses.