Kotlin launch原理全面分析

2022-11-28 12:52 开发作者：且听真言

一、协程是如何创建的

launch、async 可以创建、启动新的协程,那么协程到底是如何创建的？

  runblocking {
        println(Thread.currentThread().name)
        launch {
            println(Thread.currentThread().name)
            delay(100L)
        }
        Thread.sleep(1000L)
    }
Log
main @coroutine#1
main @coroutine#2
Process finished with exit code 0

runBlocking{} 启动了第一个协程，launch{} 启动了第二个协程。

协程启动的基础API

public fun <T> (suspend () -> T).createCoroutine(
    completion: Continuation<T>
): Continuation<Unit> =
    SafeContinuation(createCoroutineUnintercepted(completion).intercepted(), COROUTINE_SUSPENDED)
public fun <T> (suspend () -> T).startCoroutine(
    completion: Continuation<T>
) {
    createCoroutineUnintercepted(completion).intercepted().resume(Unit)
}

createCoroutine{}、startCoroutine{}就是 Kotlin 协程当中最基础的两个创建协程的 API。启动协程有三种常见的方式：launch、runBlocking、async。它们其实属于协程中间层提供的 API，而它们的底层都调用了“基础层”的协程 API。

createCoroutine{}、startCoroutine{}是扩展函数，其扩展接收者类型是一个函数类型：suspend () -> T，代表了“无参数，返回值为 T 的挂起函数或者 Lambda”。而对于函数本身，它们两个都接收一个 Continuation<T> 类型的参数，其中一个函数，还会返回一个 Continuation<Unit> 类型的返回值。

val block = suspend {
    println("Hello")
    delay(1000L)
    println("World!")
    "Result"
}
fun testLaunch2() {
    val continuation = object : Continuation<String> {
        override val context: CoroutineContext
            get() = EmptyCoroutineContext
        override fun resumeWith(result: Result<String>) {
            println("Result:" + result.getOrNull())
        }
    }
    block.startCoroutine(continuation)
}
fun main() {
    testLaunch2()
    Thread.sleep(2000L)
}
Log
Hello
World!
Result:Result
Process finished with exit code 0

类型为suspend () -> T的函数或者Lambda 表达式可以用 block.startCoroutine() 来启动协程了。

Continuation 有两种用法，一种是在实现挂起函数的时候，用于传递挂起函数的执行结果；另一种是在调用挂起函数的时候，以匿名内部类的方式，用于接收挂起函数的执行结果。

使用 createCoroutine() 这个方法其实上面代码的逻辑：

fun testLaunch3() {
    val continuation = object : Continuation<String> {
        override val context: CoroutineContext
            get() = EmptyCoroutineContext
        override fun resumeWith(result: Result<String>) {
            println("Result:" + result.getOrNull())
        }
    }
    val coroutinue = block.createCoroutine(continuation)
    coroutinue.resume(Unit)
}
val block = suspend {
    println("Hello")
    delay(1000L)
    println("World!")
    "Result"
}
fun main() {js
    testLaunch3()
    Thread.sleep(2000L)
}
Log
Hello
World!
Result:Result
Process finished with exit code 0

createCoroutine() 创建一个协程，先不启动。调用 resume() 才能启动。createCoroutine()、startCoroutine() 的源代码差别也并不大，只是前者没有调用 resume()，而后者调用了 resume()。startCoroutine() 之所以可以创建并同时启动协程的原因就在于，它在源码中直接调用了 resume(Unit)。

将 startCoroutine()转换为Java：

package com.example.myapplication.testcoroutinue;
import kotlin.Metadata;
import kotlin.Result;
import kotlin.ResultKt;
import kotlin.Unit;
import kotlin.coroutines.Continuation;
import kotlin.coroutines.ContinuationKt;
import kotlin.coroutines.CoroutineContext;
import kotlin.coroutines.EmptyCoroutineContext;
import kotlin.coroutines.intrinsics.IntrinsicsKt;
import kotlin.jvm.functions.Function1;
import kotlin.jvm.internal.Intrinsics;
import kotlinx.coroutines.DelayKt;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
@Metadata(
   mv = {1, 6, 0},
   k = 2,
   d1 = {"\u0000\u001e\n\u0000\n\u0002\u0018\u0002\n\u0002\u0018\u0002\n\u0002\u0010\u000e\n\u0002\u0010\u0000\n\u0002\b\u0004\n\u0002\u0010\u0002\n\u0002\b\u0002\u001a\u0006\u0010\b\u001a\u00020\t\u001a\u0006\u0010\n\u001a\u00020\t\",\u0010\u0000\u001a\u0018\b\u0001\u0012\n\u0012\b\u0012\u0004\u0012\u00020\u00030\u0002\u0012\u0006\u0012\u0004\u0018\u00010\u00040\u0001\u0001\u0000\u0006\n\n\u0002\u0010\u0007\u001a\u0004\b\u0005\u0010\u0006\u0082\u0002\u0004\n\u0002\b\u0019\u0006\u000b"},
   d2 = {"block", "Lkotlin/Function1;", "Lkotlin/coroutines/Continuation;", "", "", "getBlock", "()Lkotlin/jvm/functions/Function1;", "Lkotlin/jvm/functions/Function1;", "main", "", "testLaunch2", "My_Application.app.main"}
)
public final class TestCoroutinue888Kt {
// Kotlin 为 block 变量生成的静态变量
   @NotNull
   private static final Function1 block;
   public static final void main() {
      testLaunch2();
      Thread.sleep(2000L);
   }
   // $FF: synthetic method
   public static void main(String[] var0) {
      main();
   }
    // Kotlin 为 block 变量生成的静态变量以及方法
   @NotNull
   public static final Function1 getBlock() {
      return block;
   }
   public static final void testLaunch2() {
//continuation 变量对应的匿名内部类
      <undefinedtype> continuation = new Continuation() {
         @NotNull
         public CoroutineContext getContext() {
            return (CoroutineContext)EmptyCoroutineContext.INSTANCE;
         }
         public void resumeWith(@NotNull Object result) {
            String var2 = "Result:" + (String)(Result.isFailure-impl(result) ? null : result);
            System.out.println(var2);
         }
      };
//block.startCoroutine(continuation) 转换成了ContinuationKt.startCoroutine(block, (Continuation)continuation)
      ContinuationKt.startCoroutine(block, (Continuation)continuation);
   }
   static {
    //实现了 Continuation 接口
      Function1 var0 = (Function1)(new Function1((Continuation)null) {
         int label;
//invokeSuspend()为协程状态机逻辑
         @Nullable
         public final Object invokeSuspend(@NotNull Object $result) {
            Object var3 = IntrinsicsKt.getCOROUTINE_SUSPENDED();
            String var2;
            switch(this.label) {
            case 0:
               ResultKt.throwOnFailure($result);
               var2 = "Hello";
               System.out.println(var2);
               this.label = 1;
               if (DelayKt.delay(1000L, this) == var3) {
                  return var3;
               }
               break;
            case 1:
               ResultKt.throwOnFailure($result);
               break;
            default:
               throw new IllegalStateException("call to 'resume' before 'invoke' with coroutine");
            }
            var2 = "World!";
            System.out.println(var2);
            return "Result";
         }
         @NotNull
         public final Continuation create(@NotNull Continuation completion) {
            Intrinsics.checkNotNullParameter(completion, "completion");
            Function1 var2 = new <anonymous constructor>(completion);
            return var2;
         }
         public final Object invoke(Object var1) {
            return ((<undefinedtype>)this.create((Continuation)var1)).invokeSuspend(Unit.INSTANCE);
         }
     python });
      block = var0;
   }
}

public fun <T> (suspend () -> T).startCoroutine(
    completion: Continuation<T>
) {
createCoroutineUnintercepted(completion).intercepted().resume(Unit)
}

在 startCoroutine() 当中，首开发者_Python先会调用 createCoroutineUnintercepted() 方法。

public expect fun <T> (suspend () -> T).createCoroutineUnintercepted(
    completion: Continuation<T>
): Continuation<Unit>

代码中的 expect，一种声明，由于 Kotlin 是面向多个平台的，具体的实现，就需要在特定的平台实现。

public actual fun <T> (suspend () -> T).createCoroutineUnintercepted(
    completion: Continuation<T>
): Continuation<Unit> {
    val probeCompletion = probeCoroutineCreated(completion)
    return if (this is BaseContinuationImpl)
        create(probeCompletion)
    else
        createCoroutineFromSuspendFunction(probeCompletion) {
            (this as Function1<Continuation<T>, Any?>).invoke(it)
        }
}

actual，代表了 createCoroutineUnintercepted() 在 JVM 平台的实现。

createCoroutineUnintercepted() 是一个扩展函数，this代表了 block 变量。(this is BaseContinuationImpl) 条件为ture，就会调用 create(probeCompletion)。

public open fun create(completion: Continuation<*>): Continuation<Unit> {
    throw UnsupportedOperationException("create(Continuation) has not been overridden")
}

在默认情况下，这个 create() 方法是会抛出异常的。

         @NotNull
         public final Continuation create(@NotNull Continuation completion) {
            Intrinsics.checkNotNullParameter(completion, "completion");
            Function1 var2 = new <anonymous constructor>(completion);
            return var2;
         }

返回了Continuation 对象。

public fun <T> (suspend () -> T).startCoroutine(
    completion: Continuation<T>
) {
createCoroutineUnintercepted(completion).intercepted().resume(Unit)
}

intercepted() 在JVM 实现如下：

public actual fun <T> Continuation<T>.intercepted(): Continuation<T> =
    (this as? ContinuationImpl)?.intercepted() ?: this

将 Continuation 强转成了 ContinuationImpl，调用了它的 intercepted()。

ContinuationImpl 的源代码:

internal abstract class ContinuationImpl(
    completion: Continuati编程on<Any?>?,
    private val _context: CoroutineContext?
) : BaseContinuationImpl(completion) {
    @Transient
    private var intercepted: Continuation<Any?>? = null
    public fun intercepted(): Continuation<Any?> =
        intercepted
            ?: (context[ContinuationInterceptor]?.interceptContinuation(this) ?: this)
                .also { interce编程客栈pted = it }
}

通过 ContinuationInterceptor，对 Continuation 进行拦截，从而将程序的执行逻www.devze.com辑派发到特定的线程之上。

resume(Unit)：

public fun <T> (suspend () -> T).startCoroutine(
    completion: Continuation<T>
) {
createCoroutineUnintercepted(completion).intercepted().resume(Unit)
}

resume(Unit)，作用其实就相当于启动了协程。

二、launch 是如何启动协程的

fun main() {
    testLaunch11()
    Thread.sleep(2000L)
}
fun testLaunch11() {
    val coroutineScope = CoroutineScope(Job())
    coroutineScope.launch {
        println("Hello")
        delay(1000L)
        println("World!")
    }
}
Log
Hello
World!
Process finished with exit code 0

转Java

package com.example.myapplication.testcoroutinue;
import kotlin.Metadata;
import kotlin.ResultKt;
import kotlin.Unit;
import kotlin.coroutines.Continuation;
import kotlin.coroutines.CoroutineContext;
import kotlin.coroutines.intrinsics.IntrinsicsKt;
import kotlin.jvm.functions.Function2;
import kotlin.jvm.internal.Intrinsics;
import kotlinx.coroutines.BuildersKt;
import kotlinx.coroutines.CoroutineScope;
import kotlinx.coroutines.CoroutineScopeKt;
import kotlinx.coroutines.CoroutineStart;
import kotlinx.coroutines.DelayKt;
import kotlinx.coroutines.Job;
import kotlinx.coroutines.JobKt;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
@Metadata(
   mv = {1, 6, 0},
   k = 2,
   d1 = {"\u0000\n\n\u0000\n\u0002\u0010\u0002\n\u0002\b\u0002\u001a\u0006\u0010\u0000\u001a\u00020\u0001\u001a\u0006\u0010\u0002\u001a\u00020\u0001\u0006\u0003"},
   d2 = {"main", "", "testLaunch11", "My_Application.app.main"}
)
public final class TestCoroutinue999Kt {
   public static final void main() {
      testLaunch11();
      Thread.sleep(2000L);
   }
   // $FF: synthetic method
   public static void main(String[] var0) {
      main();
   }
   public static final void testLaunch11() {
      CoroutineScope coroutineScope = CoroutineScopeKt.CoroutineScope((CoroutineContext)JobKt.Job$default((Job)null, 1, (Object)null));
//对应 launch 当中的 Lambda。
      BuildersKt.launch$default(coroutineScope, (CoroutineContext)null, (CoroutineStart)null, (Function2)(new Function2((Continuation)null) {
         int label;
         @Nullable
         public final Object invokeSuspend(@NotNull Object $result) {
            Object var3 = IntrinsicsKt.getCOROUTINE_SUSPENDED();
            String var2;
            switch(this.label) {
            case 0:
               ResultKt.throwOnFailure($result);
               var2 = "Hello";
               System.out.println(var2);
               this.label = 1;
               if (DelayKt.delay(1000L, this) == var3) {
                  return var3;
               }
               break;
            case 1:
               ResultKt.throwOnFailure($result);
               break;
            default:
               throw new IllegalStateException("call to 'resume' before 'invoke' with coroutine");
            }
            var2 = "World!";
            System.out.println(var2);
            return Unit.INSTANCE;
         }
         @NotNull
         public final Continuation create(@Nullable Object value, @NotNull Continuation completion) {
            Intrinsics.checkNotNullParameter(completion, "completion");
            Function2 var3 = new <anonymous constructor>(completion);
            return var3;
         }
         public final Object invoke(Object var1, Object var2) {
            return ((<undefinedtype>)this.create(var1, (Continuation)var2)).invokeSuspend(Unit.INSTANCE);
         }
      }), 3, (Object)null);
   }
}

launch源码

public fun CoroutineScope.launch(
    context: CoroutineContext = EmptyCoroutineContext,
    start: CoroutineStart = CoroutineStart.DEFAULT,
    block: suspend CoroutineScope.() -> Unit
): Job {
    //launch 会根据传入的 CoroutineContext 创建出新的 Context。
    val newContext = newCoroutineContext(context)
    //launch 会根据传入的启动模式来创建对应的协程对象。这里有两种，一种是标准的，一种是懒加载的。
    val coroutine = if (start.isLazy)
        LazyStandaloneCoroutine(newContext, block) else
        StandaloneCoroutine(newContext, active = true)
    //启动协程。
    coroutine.start(start, coroutine, block)
    return coroutine
}

coroutine.start() :

public abstract class AbstractCoroutine<in T>(
    parentContext: CoroutineContext,
    initParentJob: Boolean,
    active: Boolean
) : JobSupport(active), Job, Continuation<T>, CoroutineScope {
    public fun <R> start(start: CoroutineStart, receiver: R, block: suspend R.() -> T) {
        start(block, receiver, this)
    }
}

AbstractCoroutine.kt 对应协程的抽象逻辑。AbstractCoroutine 的start() 方法，用于启动协程。

public enum class CoroutineStart {
    public operator fun <T> invoke(block: suspend () -> T, completion: Continuation<T>): Unit =
        when (this) {
            DEFAULT -> block.startCoroutineCancellable(completion)
            ATOMIC -> block.startCoroutine(completion)
            UNDISPATCHED -> block.startCoroutineUndispatched(completion)
            LAZY -> Unit // will start lazily
        }
}

start(block, receiver, this)，进入 CoroutineStart.invoke()。

invoke() 方法当中，根据 launch 传入的启动模式，以不同的方式启动协程。当启动模式是 ATOMIC 的时候，就会调用 block.startCoroutine(completion)。startCoroutineUndispatched(completion) 和 startCoroutineCancellable(completion)，只是在 startCoroutine() 的基础上增加了一些额外的功能而已。前者代表启动协程以后就不会被分发，后者代表启动以后可以响应取消。

startCoroutineCancellable(completion)

public fun <T> (suspend () -> T).startCoroutineCancellable(completion: Continuation<T>): Unit = runSafely(completion) {
    createCoroutineUnintercepted(completion).intercepted().resumeCancellableWith(Result.success(Unit))
}
public actual fun <T> (suspend () -> T).createCoroutineUnintercepted(
    completion: Continuation<T>
): Continuation<Unit> {
    val probeCompletion = probeCoroutineCreated(completion)
    return if (this is BaseContinuationImpl)
        create(probeCompletion)
    else
        createCoroutineFromSuspendFunction(probeCompletion) {
            (this as Function1<Continuation<T>, Any?>).invoke(it)
        }
}

startCoroutineCancellable() 的源代码，会调用 createCoroutineUnintercepted()，然后调用 create(probeCompletion)，然后最终会调用create() 方法。launch 这个 API，只是对协程的基础元素 startCoroutine() 等方法进行了一些封装而已。

到此这篇关于Kotlin launch原理全面分析的文章就介绍到这了,更多相关Kotlin launch内容请搜索我们以前的文章或继续浏览下面的相关文章希望大家以后多多支持我们！

继续阅读：Kotlin launch Kotlin launch原理

Kotlin launch原理全面分析

目录

一、协程是如何创建的

协程启动的基础API

二、launch 是如何启动协程的

更多精彩内容

精彩评论

最新开发

C# 从字符串中分离文件路径、文件名及扩展名的操作

springboot 整合 nacos 配置实现多个环境不同配置

Maven项目如何在pom文件中引入lib下的第三方jar包并打包进去

Java线程池实现带返回值的方式方法

SpringBoot最常用的50个注解总结(全是干货！)

开发排行榜

springboot后端存储富文本内容的思路与步骤(含图片内容)

PyCharm运行python测试,报错“没有发现测试”/“空套件”的解决

return base64.b64encode(b).decode(

基于C语言实现钻石棋游戏的示例代码

Sublime Text 3解决中文乱码问题（实测可用）