HTTPCookieStorage: rewrite access to shared storage

[Alexander-Ignition]

Removed access to sharedStorage through sharedSyncQ because the static constants are initialized lazily and in a thread-safe.

[Alexander-Ignition]

@swift-ci please test

[spevans]

@swift-ci please test

[pushkarnk]

I guess we have shared as a class var because the API doc says so. And hence the synchronisation. However, I can see that HTTPCookieStorage.shared on Darwin is get-only, but it could have an internal or private setter. In short, I can't be sure if shared should be made a constant.

@millenomi @spevans Any thoughts?

[spevans]

private(set) var should work to make the public access read-only.

[pushkarnk]

@Alexander-Ignition Eager to know your thoughts too.

[Alexander-Ignition]

Actually we don’t need sync code because of static is thread-safe by default. I checked no one change shared property (internally), so we don’t need public var or private(set) var. This approach with private static let and computed property for interface is common style in Foundation. NotificationCenter , FileManager , URLSession

[pushkarnk]

Right, if we agree to make it a constant (class let shared), then there's no need for the sync. But the question is: given that the API doc defines it as a class var shared (though publicly read-only), should we change it to a constant? I'm not sure if the Darwin's Foundation has internal/private setters defined. I just want to be careful about the parity.

[pushkarnk]

cc @ianpartridge @weissi

[spevans]

The public API only defines a getter so I don't think its a problem to use a constant internally since the API it still correct.

[pushkarnk]

@swift-ci test and merge

[pushkarnk]

@swift-ci test and merge