wenchi

import Foundation
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

// 建立一個 Serial Queue
let queue = DispatchQueue(label: "com.example.myqueue")

let blk0: @Sendable () -> Void = {
    print("blk0 start"); Thread.sleep(forTimeInterval: 2); print("blk0 end")