How to stop a method while it's running in swiftui - swiftui

Question

I have a problem and I have to find a solution. I must immediately stop the "Starting" method if the user presses the Cancel button.
I have not fixed the problem yet because I can not block the method while it is running but only at the end or at the beginning of the execution.
ContentView:
Button(action: {
self.Starting()
DispatchQueue.main.asyncAfter(deadline: .init(uptimeNanoseconds: 0), execute: self.workItem)
}) {
Text("START")
}
Button(action: {
self.workItem.cancel()
}) {
Text("CANCEL")
}
Starting method:
func Starting() {
self.workItem = DispatchWorkItem {
DispatchQueue.main.async {
self.impostazioniChek=true
}
DispatchQueue.global().async {
if (self.pm.MarksSwitch)
{
sleep(UInt32(self.MarksT))
self.Marks()
}
if (self.pm.ReadySwitch)
{
sleep(UInt32(self.ReadyT))
self.Ready()
}
self.Start()
sleep(3)
DispatchQueue.main.async {
self.tm.start()
}
}
}
}

Answer 1

You cannot cancel because
1) almost all the time work items runs on main (UI) queue, so block it
2) inside work item there is no check for isCancelled. DispatchWorkItem.cancel() only marks it cancelled, but does not stops execution you have to do this.
So to make this work it needs to redirect everything not-UI related in your work item into .background queue explicitly.
Eg. instead of
DispatchQueue.main.asyncAfter(deadline: .init(uptimeNanoseconds: 0), execute: self.workItem)
use
DispatchQueue.global(qos: .background).async { self.workItem }
Instead of
DispatchQueue.global().async {
if (self.pm.MarksSwitch)
Just use (because it is already in background)
if (self.pm.MarksSwitch)
and I'm not sure what is (probably it also should be run on background queue)
self.tm.start()
And on second add inside block interruption on cancellation by regular check, like below
...
}
if self.workItem.isCancelled { // add as many such as needed
return
}
if (self.pm.ReadySwitch)
...