custom-globalactor.swift

@available(macOS 14, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
final class DispatchSerialExecutor: SerialExecutor {
    let queue: DispatchQueue

    init(queue: DispatchQueue) {
        self.queue = queue
    }

    init() {
        self.queue = DispatchQueue(
            label: "software.unbeatable.dispatch-serial-executor",
            attributes: .concurrent
        )
    }

    static let global = DispatchSerialExecutor(queue: .global())

    func enqueue(_ job: UnownedJob) {
        queue.async { [job] in
            job.runSynchronously(on: self.asUnownedSerialExecutor())
        }
    }

    func asUnownedSerialExecutor() -> UnownedSerialExecutor {
        UnownedSerialExecutor(ordinary: self)
    }
}

@globalActor fileprivate actor GlobalQueueActor {
    static let shared = GlobalQueueActor()
    
    nonisolated private let executor = DispatchSerialExecutor.global
    nonisolated var unownedExecutor: UnownedSerialExecutor {
        executor.asUnownedSerialExecutor()
    }
}