CODEWITHSUNDEEP
swiftthread-safetyswift6
j.s.com
j.s.com

Reputation: 1478

Var 'xxx' is not concurrency-safe because it is non-isolated global shared mutable state; this is an error in Swift 6

I use some global variables, only Integer, which can be accessed from several threads. Under normal circumstances only one thread writes this variable but other threads read them.

var xxx: Integer = 0

What must be done to make this variable thread-safe for Swift 6?

Can somebody give me a simple example, how to handle my few global variables. The variables are currently not part of a class/struct. Only simple variables.

Upvotes: 3

Views: 426

Answers (1)

Sweeper
Sweeper

Reputation: 273540

From SE-0412,

Under strict concurrency checking, require every global variable to either be isolated to a global actor or be both:

  1. immutable
  2. of Sendable type

Since your variable must be a var, it must be isolated to a global actor. You can use an existing global actor like @MainActor:

@MainActor
var x = 0

Or write your own global actor

@globalActor
public struct SomeGlobalActor {
  public actor MyActor { }

  public static let shared = MyActor()
}

@SomeGlobalActor 
var x = 0

In either case, you would need an await to access this from a context not isolated to the global actor.

Finally, if you want to synchronise access to this global variable in your own way, you can do:

nonisolated(unsafe) var x = 0

This gives up the compile-time thread-safety checks that Swift does for you.

Upvotes: 3

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