Thread safety of method calls on “shared” static constant property

问题

I have a Swift class which uses a traditional Cocoa singleton pattern: one static shared constant and a private init that is only called once for that shared constant. It's like this:

public class Foo {
    public static let shared = Foo()

    private init() { /* ... */ }

    public func bar() { /* ... */ }
    public func baz() { /* ... */ }
}

// Meanwhile, in multiple places upon multiple threads:

Foo.shared.bar()

Foo.shared.baz()

If I have a dozen threads calling functions on that constant, does it pause all calls until that initializer completes, or should I have some protections within those instance functions to wait for initialization to complete?

来源：https://stackoverflow.com/questions/54189782/thread-safety-of-method-calls-on-shared-static-constant-property