How to detect memory warnings in iOS App Extension

Question

I'm writing an iOS extension that extends NEPacketTunnelProvider in the NetworkExtension framework released in iOS 9. I'm running into a situation where iOS is killing the extension once hits 6MB of memory used.

In a regular iOS app, there are two ways to detect memory warnings and do something about it. Either via [UIApplicationDelegate applicationDidReceiveMemoryWarning:(UIApplication*)app] or [UIViewController didReceiveMemoryWarning]

Is there a similar way to detect memory warnings within an extension? I've searched up and down the iOS extension documentation but have come up empty thus far.

Answer 1

I am not very familiar with the extensions API, however my basic hunch says that you can register any of your object as observers of UIApplicationDidReceiveMemoryWarningNotification from within that class:

NSNotificationCenter.defaultCenter().addObserverForName(UIApplicationDidReceiveMemoryWarningNotification,
  object: nil, queue: .mainQueue()) { notification in
    print("Memory warning received")
}

Answer 2

ozgur's answer does not work. UIApplicationDidReceiveMemeoryWarningNotification is a UIKit event and I haven't found a way to get access to that from an extension. The way to go is the last of these options: DISPATCH_SOURCE_TYPE_MEMORYPRESSURE.

I've used the following code (Swift) in a Broadcast Upload Extension and have confirmed with breakpoints that it is called during a memory event right before the extension conks out.

let source = DispatchSource.makeMemoryPressureSource(eventMask: .all, queue: nil)

let q = DispatchQueue.init(label: "test")
q.async {
    source.setEventHandler {
        let event:DispatchSource.MemoryPressureEvent  = source.mask
        print(event)
        switch event {
        case DispatchSource.MemoryPressureEvent.normal:
            print("normal")
        case DispatchSource.MemoryPressureEvent.warning:
            print("warning")
        case DispatchSource.MemoryPressureEvent.critical:
            print("critical")
        default:
            break
        }
        
    }
    source.resume()
}