Swift 5.5 Actor impl with stealing GlobalActor's Executors https://twitter.com/inamiy/status/1514076289443176453

actor-custom-executor.swift

import Foundation
import _Concurrency

actor SomeSystem {
    nonisolated var unownedExecutor: UnownedSerialExecutor {
        #if os(Linux)
        MyActor.sharedUnownedExecutor
        #else
        MainActor.sharedUnownedExecutor
        #endif
    }

    func hello() {
        print(Thread.current) // main thread
    }
}

@globalActor
actor MyActor {
    static let shared = MyActor()
}

Task {
    let system = SomeSystem()
    await system.hello()
}