In Swift 6, the compiler checks are much more reliable. The basis for thread-safe data processing in Swift 6 is Sendable. The protocol is designed for the exchange of values between threads.

Java Threads, Second Edition, Scott Oaks and Henry Wong (O’Reilly) Concurrent Programming in Java, Second Edition, Doug Lea (Addison-Wesley) Taming Java Threads, Allen Holub (Apress) ...