模仿kotlin协程实现原理，手写一个协程，实现异步业务同步操作_kotlin协程 自实现

// An highlighted block
         
fun main() {
    /**
     * println("start") //主线程
     * val user = getUserInfo() //耗时
     * println(user) //主线程
     * val friendList = getFriendList(user)//耗时
     * println(friendList)//主线程
     * val feedList= getFeedList(friendList)//耗时
     * println(feelList)//主线程
     */
    //主线程调用
    Main.execute {
        loginWebsintFun(LoginWebsiteImpl())
    }

}


//主线程
val Main = Executors.newSingleThreadExecutor { runnable -> Thread(runnable).also { it.name = "main" } }

//IO线程
val Io = Executors.newSingleThreadExecutor { runnable -> Thread(runnable).also { it.name = "Io" } }

//Callback
interface Continuation<in T> {
    fun resumeWith(result: T)
}

class LoginWebsiteImpl : Continuation<String> {
    var label: Int = 0
    var result: String? = null

    override fun resumeWith(_result: String) {
        result = _result
        return loginWebsintFun(this)
    }


}

fun loginWebsintFun(continuateion: LoginWebsiteImpl) {
    when (continuateion.label) {
        0 -> {
            println("start thread:" + Thread.currentThread().name)
            continuateion.label = 1
            if (getUserInfo(continuateion) == 1) {
                return
            }
        }
        1 -> {
            println("result: ${continuateion.result} " + Thread.currentThread().name)
            continuateion.label = 2
            if (getFriendList(continuateion.result!!, continuateion) == 1) {
                return
            }
        }
        2 -> {
            println("result ${continuateion.result} " + Thread.currentThread().name)
            continuateion.label = 3
            if (getFeedList(continuateion.result!!, continuateion) == 1) {
                return
            }
        }
        3->{
            println("result ${continuateion.result} " + Thread.currentThread().name)
        }
    }
}


//step1
fun getUserInfo(continuation: Continuation<String>): Any? {
    Io.execute {
        //开始执行耗时操作
        println("getUseInfo.... thread:" + Thread.currentThread().name)
        Thread.sleep(1000)
        //操作完成，进行下一步
        Main.execute { continuation.resumeWith("userName:Tom") }
    }
    return 1
}

//step2
fun getFriendList(userName: String, continuation: Continuation<String>): Any? {
    Io.execute {
        //开始执行耗时操作
        println("getFriendList by ${userName}..... thread:" + Thread.currentThread().name)
        Thread.sleep(1000)
        //操作完成，进行下一步
        Main.execute { continuation.resumeWith("Li,Wang,Zhang") }
    }
    return 1
}

//step3
fun getFeedList(friendList: String, continuation: Continuation<String>): Any {
    Io.execute {
        //开始执行耗时操作
        println("getFeedList by ${friendList}..... thread:" + Thread.currentThread().name)
        Thread.sleep(1000)
        //操作完成，进行下一步
        Main.execute { continuation.resumeWith("feed1,feed2,feed3") }
    }
    return 1
}
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运行结果

引用
https://mp.weixin.qq.com/s/nXfweTaOCpm6Bj34rW-wLA

https://www.bennyhuo.com/2019/05/07/coroutine-suspend