demo Swift3 memory pressureEvent use DispatchSource API

Swift3_memory_pressureEvent.swift

import Foundation

class A {
    var d:[Int]?
    init(len:Int) {
        d = Array(repeating: 0, count: len)
    }
}

func test() {
    installMemoryWarning()
    
    var b :[A] = []
    for _ in 0 ... 2000 {
        let c = A.init(len: 1024 * 1000*3 )
        b.append(c)
        
        sleep(1)
    }
}
func installMemoryWarning(){
    
    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()
    }
}

Hi, thanks for this useful snippet! Especially as I've been having a hard time finding an official Apple source for this.

It seems like line 28 should be getting the source.data, not source.mask. When I run the example I keep getting .all, which is indeed the mask we requested in makeMemoryPressureSource(eventMask:queue:).