A Queue (FIFO) built from an actor.

Queue.swift

actor Queue {
    private var tasks: [() async -> Void] = []
    
    func enqueue(_ task: @escaping () async -> Void) {
        tasks.append(task)
        Task { await runNext() }
    }
    
    private func runNext() async {
        guard !tasks.isEmpty else { return }
        let task = tasks.removeFirst()
        await task()
        if !tasks.isEmpty {
            Task { await runNext() }
        }
    }
}