Data races are now clearly diagnosed
Data races are now clearly diagnosed 관련
Available from Swift 5.10
Swift concurrency was introduced back in Swift 5.5, but had a bit of a rocky adoption both in Apple's own frameworks and our own projects. However, with Swift 5.10 the team made a rather dramatic statement: "Swift 5.10 closes all known static data-race safety holes in complete strict concurrency checking."
Concurrency checking is what allows the compiler to verify our use of concurrent code is safe – that we aren't accidentally sharing mutable state in a way that can cause race conditions. Of course, the key word here is "known": everything they know about has been resolved.
Apple's work here is not only hugely innovative, but hugely complex: similar to how type inference requires the Swift compiler to be able to reason about how various parts of our code are used, in concurrency the compiler is effectively running a series of algorithms that attempt to determine conclusively that our code is concurrency-safe.
To give you a concrete example, this code generated a warning in Swift 5.9:
import SwiftUI
struct ContentView: View {
var body: some View {
Button("Tap Me", action: doWork)
}
func doWork() {
print("Hello")
}
}
That would throw up the rather unhelpful warning, "Converting function value of type @MainActor () -> () to () -> Void loses global actor MainActor".
The problem here is that SwiftUI's Button view doesn't use @MainActor for its action, so Swift was throwing up a warning that we were calling a main actor-method from somewhere that isn't isolated to the main actor. This warning has been removed by the concurrency checking improvements in Swift 5.10: the compiler can now see the button action exists in side the body property, which is isolated to the main actor, and therefore is safe.
Other Changes in Swift 5.10