This is the AsyncOperation-class from the blogpost: https://zeitschlag.net/asyncoperation/

AsyncOperation.swift

import Foundation

class AsyncOperation: Operation {
    
    private var asyncOperationFinished: Bool
    private var asyncOperationExecuting: Bool
    
    override init() {
        self.asyncOperationFinished = false
        self.asyncOperationExecuting = false
        
        super.init()
    }
    
    override var isFinished: Bool {
        return self.asyncOperationFinished
    }
    
    override var isExecuting: Bool {
        return self.asyncOperationExecuting
    }
    
    override func start() {
        if (self.isCancelled) {
            self.willChangeValue(for: \AsyncOperation.isFinished)
            self.asyncOperationFinished = true
            self.didChangeValue(for: \AsyncOperation.isFinished)
            return
        }
        
        self.willChangeValue(for: \AsyncOperation.isExecuting)
        self.asyncOperationExecuting = true
        Thread.detachNewThreadSelector(#selector(main), toTarget: self, with: nil)
        self.didChangeValue(for: \AsyncOperation.isExecuting)
    }
    
    override func cancel() {
        super.cancel()
        self.completeOperation()
    }
    
    func operationCompletedSuccessfully() {
        self.completeOperation()
    }
    
    private func completeOperation() {
        self.willChangeValue(for: \AsyncOperation.isFinished)
        self.willChangeValue(for: \AsyncOperation.isExecuting)
        
        self.asyncOperationExecuting = false
        self.asyncOperationFinished = true
        
        self.didChangeValue(for: \AsyncOperation.isFinished)
        self.didChangeValue(for: \AsyncOperation.isExecuting)
    }
    
}