Use DispatchGroups to achieve this. You can either get notified when the group's enter() and leave() calls are balanced:
func myFunction() {
var a: Int?
let group = DispatchGroup()
group.enter()
DispatchQueue.main.async {
a = 1
group.leave()
}
// does not wait. But the code in notify() gets run
// after enter() and leave() calls are balanced
group.notify(queue: .main) {
print(a)
}
}
or you can wait:
func myFunction() {
var a: Int?
let group = DispatchGroup()
group.enter()
// avoid deadlocks by not using .main queue here
DispatchQueue.global(attributes: .qosDefault).async {
a = 1
group.leave()
}
// wait ...
group.wait()
print(a) // you could also `return a` here
}
Note: group.wait() blocks the current queue (probably the main queue in your case), so you have to dispatch.async on another queue (like in the above sample code) to avoid a deadlock.