suspend fun backgroundTask(param: Int): Int {
     // long running operation
}

fun backgroundTask(param: Int, callback: Continuation<Int>): Int {
   // long running operation
}

// 三個基于回調(diào)的 API
fun requestToken(block: (String) -> Unit)
fun createPost(
  token: String,
  item: Item,
  block: (Post) -> Unit)
)
fun processPost(post: Post)
fun postItem(item: Item) {
  requestToken { token ->
    createPost(token, item) { post ->
      processPost(post)
    }
  }
}

suspend fun requestToken(): String
suspend fun createPost(token: String, item: Item): Post
suspend fun processPost(post)
suspend fun postItem(item: Item) {
  val token = ?? requestToken()
  val post = ?? createPost(token, item)
  ?? processPost(post)
}

suspend fun getUserInfo(): String {
    withContext(Dispatchers.IO) {
        delay(1000L)
    }
    return "BoyCoder"
}

@Dao
interface RegisterDatabaseDao {
    @Insert
    suspend fun insert(register: RegisterEntity)
    //@Delete
    //suspend  fun deleteSubscriber(register: RegisterEntity):Int
    @Query("SELECT * FROM Register_users_table ORDER BY userId DESC")
    fun getAllUsers(): LiveData<List<RegisterEntity>>
    @Query("DELETE FROM Register_users_table")
    suspend fun deleteAll(): Int
    @Query("SELECT * FROM Register_users_table WHERE user_name LIKE :userName")
    suspend fun getUsername(userName: String): RegisterEntity?
}

import kotlinx.coroutines.*
import java.util.*
import java.time.LocalDate
import java.time.format.DateTimeFormatter
import java.time.Period
import java.text.SimpleDateFormat
import java.lang.Thread
var dateTimeNow = ""
@OptIn(DelicateCoroutinesApi::class)
fun main() = runBlocking{
    dateTimeNow = dateAsString(Calendar.getInstance().time.time)
    println("code start: ${dateTimeNow}")
    launch { 
        dateTimeNow = dateAsString(Calendar.getInstance().time.time)
    	println("1 code start: ${dateTimeNow}")
        delay(2000L)
        dateTimeNow = dateAsString(Calendar.getInstance().time.time)
        println("2 Task from runBlocking: ${dateTimeNow}")
    }
    coroutineScope { // Creates a new coroutine scope
        dateTimeNow = dateAsString(Calendar.getInstance().time.time)
        println("3 coroutineScope created: ${dateTimeNow}")
        val job = launch {
            dateTimeNow = dateAsString(Calendar.getInstance().time.time)
            println("4 coroutineScope job starts: ${dateTimeNow}")
            val one = doSomethingUsefulOne()
        	  val two = doSomethingUsefulTwo()
            dateTimeNow = dateAsString(Calendar.getInstance().time.time)
            println("5 coroutineScope job ends: ${dateTimeNow}")
        }
        val job2 = launch {
            dateTimeNow = dateAsString(Calendar.getInstance().time.time)
            println("11 coroutineScope job2 starts: ${dateTimeNow}")
        }
        delay(1000L)
        dateTimeNow = dateAsString(Calendar.getInstance().time.time)
        println("6 Task from first coroutine scope: ${dateTimeNow}") // Printed before initial launch
        //job.cancel() // This cancels nested launch's execution
    }
    dateTimeNow = dateAsString(Calendar.getInstance().time.time)
    println("code end: ${dateTimeNow}")
}
fun dateAsString(
    dateInMillis: Long,
    format: String = "yyyyMMdd HH:mm:ss",
    locale: Locale = Locale.getDefault()
): String {
    val date = Date(dateInMillis)
    val formatter = SimpleDateFormat(format, locale)
    return formatter.format(date)
}
suspend fun doSomethingUsefulOne(): Int {
    dateTimeNow = dateAsString(Calendar.getInstance().time.time)
    println("7 第一個掛起函數(shù)開始: ${dateTimeNow}")
    delay(1000L) // 假設我們在這里做了某些有用的工作
    dateTimeNow = dateAsString(Calendar.getInstance().time.time)
    println("8 第一個掛起函數(shù)結(jié)束: ${dateTimeNow}")
    return 1
}
suspend fun doSomethingUsefulTwo(): Int {
    dateTimeNow = dateAsString(Calendar.getInstance().time.time)
    println("9 第二個掛起函數(shù)開始: ${dateTimeNow}")
    delay(2000L) // 假設我們在這里也做了某些有用的工作
    dateTimeNow = dateAsString(Calendar.getInstance().time.time)
    println("10 第二個掛起函數(shù)結(jié)束: ${dateTimeNow}")
    coroutineScope {
        val job = launch {
            doSomethingUsefulThree()
            doSomethingUsefulFour()
        }
    }
    return 2
}
suspend fun doSomethingUsefulThree(): Int {
    dateTimeNow = dateAsString(Calendar.getInstance().time.time)
    println("9 第三個掛起函數(shù)開始: ${dateTimeNow}")
    delay(3000L) // 假設我們在這里也做了某些有用的工作
    dateTimeNow = dateAsString(Calendar.getInstance().time.time)
    println("10 第三個掛起函數(shù)結(jié)束: ${dateTimeNow}")
    return 3
}
suspend fun doSomethingUsefulFour(): Int {
    dateTimeNow = dateAsString(Calendar.getInstance().time.time)
    println("9 第四個掛起函數(shù)開始: ${dateTimeNow}")
    delay(3000L) // 假設我們在這里也做了某些有用的工作
    dateTimeNow = dateAsString(Calendar.getInstance().time.time)
    println("10 第四個掛起函數(shù)結(jié)束: ${dateTimeNow}")
    return 4
}