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Kotlin協(xié)程的啟動(dòng)方式介紹

更新時(shí)間：2022年09月07日 14:56:34 作者：且聽(tīng)真言

這篇文章我們來(lái)講協(xié)程的啟動(dòng)，畢竟協(xié)程是一個(gè)很強(qiáng)大的設(shè)計(jì)模式，深入了解需要花很多的時(shí)間，我們先從簡(jiǎn)單開(kāi)始，其實(shí)學(xué)會(huì)了簡(jiǎn)單的使用，基本已經(jīng)可以滿(mǎn)足我們平時(shí)的開(kāi)發(fā)需要了，話(huà)不多說(shuō)，開(kāi)始

1.GlobalScope.launch

代碼示例：

fun testGlobalScope() {
    GlobalScope.launch {
        println("Coroutinue started!")
        delay(1000L)
        println("Hello World!")
    }
    println("After launch!")
    Thread.sleep(2000L)
    println("Process end!")
}
/**
 * After launch!
 * Coroutinue started!
 * Hello World!
 * Process end!
 */

@DelicateCoroutinesApi
public object GlobalScope : CoroutineScope {
    /**
     * Returns [EmptyCoroutineContext].
     */
    override val coroutineContext: CoroutineContext
        get() = EmptyCoroutineContext
}

public fun CoroutineScope.launch(
    context: CoroutineContext = EmptyCoroutineContext,
    start: CoroutineStart = CoroutineStart.DEFAULT,
    block: suspend CoroutineScope.() -> Unit
): Job {
    val newContext = newCoroutineContext(context)
    val coroutine = if (start.isLazy)
        LazyStandaloneCoroutine(newContext, block) else
        StandaloneCoroutine(newContext, active = true)
    coroutine.start(start, coroutine, block)
    return coroutine
}

launch函數(shù)是CoroutineScope的擴(kuò)展函數(shù)，它有三個(gè)參數(shù)：

context: CoroutineContext = EmptyCoroutineContext, 第一個(gè)參數(shù)是協(xié)程上下文，它的默認(rèn)值是 EmptyCoroutineContext，如果不傳這個(gè)參數(shù)，默認(rèn)就會(huì)使用 EmptyCoroutineContext。也可以傳入 Kotlin 官方為我們提供的 Dispatchers，來(lái)指定協(xié)程運(yùn)行的線程池。（Dispatchers.IO、Dispatchers.Unconfined、Dispatchers.Main）
start: CoroutineStart = CoroutineStart.DEFAULT，第二個(gè)參數(shù)是協(xié)程的啟動(dòng)模式，默認(rèn)值是CoroutineStart.DEFAULT，CoroutineStart 是一個(gè)枚舉類(lèi)，一共有：DEFAULT、LAZY、ATOMIC、UNDISPATCHED。
block: suspend CoroutineScope.() -> Unit，第三個(gè)參數(shù)是函數(shù)類(lèi)型block，它的類(lèi)型是suspend CoroutineScope.() -> Unit。本質(zhì)是一個(gè)掛起函數(shù)。
函數(shù)的返回值是一個(gè) Job，它其實(shí)代表的是協(xié)程的句柄，并不能返回協(xié)程的執(zhí)行結(jié)果。

2.runBlocking 啟動(dòng)協(xié)程

代碼示例

fun testRunBlocking2() {
    runBlocking {
        println("Coroutinue started!")
        delay(1000L)
        println("Hello World!")
    }
    println("After Launch")
    Thread.sleep(2000L)
    println("Process end")
}
/**
 * Coroutinue started!
 * Hello World!
 * After Launch
 * Process end
 */

@Throws(InterruptedException::class)
public actual fun <T> runBlocking(context: CoroutineContext, block: suspend CoroutineScope.() -> T): T {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    val currentThread = Thread.currentThread()
    val contextInterceptor = context[ContinuationInterceptor]
    val eventLoop: EventLoop?
    val newContext: CoroutineContext
    if (contextInterceptor == null) {
        // create or use private event loop if no dispatcher is specified
        eventLoop = ThreadLocalEventLoop.eventLoop
        newContext = GlobalScope.newCoroutineContext(context + eventLoop)
    } else {
        // See if context's interceptor is an event loop that we shall use (to support TestContext)
        // or take an existing thread-local event loop if present to avoid blocking it (but don't create one)
        eventLoop = (contextInterceptor as? EventLoop)?.takeIf { it.shouldBeProcessedFromContext() }
            ?: ThreadLocalEventLoop.currentOrNull()
        newContext = GlobalScope.newCoroutineContext(context)
    }
    val coroutine = BlockingCoroutine<T>(newContext, currentThread, eventLoop)
    coroutine.start(CoroutineStart.DEFAULT, coroutine, block)
    return coroutine.joinBlocking()
}

runBlocking是普通函數(shù)，第一個(gè)參數(shù)：context: CoroutineContext,協(xié)程上下文。第二個(gè)參數(shù)是函數(shù)類(lèi)型，block: suspend CoroutineScope.() -> T,函數(shù)類(lèi)型是有返回值類(lèi)型 T 的，與 runBlocking 的返回值類(lèi)型是一樣的，runBlocking 其實(shí)是可以從協(xié)程當(dāng)中返回執(zhí)行結(jié)果的。

fun testRunBlocking() {
    val runBlockingResult = runBlocking {
        delay(500L)
        return@runBlocking "HaHa"
    }
    println("result:$runBlockingResult")
}
result:HaHa

runBlocking特點(diǎn)：

runBlocking 啟動(dòng)的協(xié)程會(huì)阻塞當(dāng)前線程的執(zhí)行。

3.async啟動(dòng)協(xié)程

使用 async{} 創(chuàng)建協(xié)程，可以通過(guò)它返回的Deferred拿到協(xié)程的執(zhí)行結(jié)果。

代碼示例

fun testAsync() {
    runBlocking {
        val deferred = async {
            println("do async:${Thread.currentThread().name}")
            delay(1000L)
            return@async "do completed"
        }
        println("After async:${Thread.currentThread().name}")
        val result = deferred.await()
        println("Result is: $result")
    }
}
After async:main @coroutine#1
do async:main @coroutine#2
Result is: do completed

public fun <T> CoroutineScope.async(
    context: CoroutineContext = EmptyCoroutineContext,
    start: CoroutineStart = CoroutineStart.DEFAULT,
    block: suspend CoroutineScope.() -> T
): Deferred<T> {
    val newContext = newCoroutineContext(context)
    val coroutine = if (start.isLazy)
        LazyDeferredCoroutine(newContext, block) else
        DeferredCoroutine<T>(newContext, active = true)
    coroutine.start(start, coroutine, block)
    return coroutine
}

async注意點(diǎn)