浅析kotlin协程launch delay调用
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作者：信仰年轻
一、简单的协程例子
这个main方法直接看成程序入口方法，此方法不带suspend修饰。
二、runBlocking 启动一个协程
runBlocking一般不在开发中使用，在测试框架中用到，连接非协程世界到协程世界，runBlocking的代码块都在coroutineScope的作用域内。
上面的main方法开启了两个协程，父协程是runBlocking启动的，子协程是里面launch启动的。父协程要等所有的子协程完成才能结束。
先看下runBlocking的源码：
public fun <T> runBlocking(context: CoroutineContext = EmptyCoroutineContext, block: suspend CoroutineScope.() -> T): T
.....
val currentThread = Thread.currentThread() //肯定是主线程
val contextInterceptor = context[ContinuationInterceptor] //拦截器，为null
val eventLoop: EventLoop? //事件轮询 handler那一套？？？
val newContext: CoroutineContext
if (contextInterceptor == null)
eventLoop = ThreadLocalEventLoop.eventLoop
newContext = GlobalScope.newCoroutineContext(context + eventLoop)
else
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) //start=create+ resumeWith(Unit)
return coroutine.joinBlocking()
启动协程时runBlocking在这里阻塞了主线程。coroutine的启动使用start，其实start= create + resumeWith（Unit）.,EventLoop参考熟悉的handler的流程，肯定存在事件队列，插入事件，取事件的操作，如事件未达处理时间就"阻塞"。
三、launch 启动一个子协程
能够启动协程的方式除了launch，还有async+await，其中async返回的是一个Deferred。
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) //启动协程了
return coroutine
public interface Deferred<out T> : Job //Deferred也是个Job
luanch的返回值是个Job，通过(coroutine.start)启动协程，在这里就作为子协程，都说子协程会继承的父协程的上下文，这是真的吗？真的。
@ExperimentalCoroutinesApi
public actual fun CoroutineScope.newCoroutineContext(context: CoroutineContext): CoroutineContext
val combined = coroutineContext + context #1
val debug = if (DEBUG) combined + CoroutineId(COROUTINE_ID.incrementAndGet()) else combined
return if (combined !== Dispatchers.Default && combined[ContinuationInterceptor] == null)
debug + Dispatchers.Default else debug
newCoroutineContext方法的作用域也是最外层coroutineScope，然后它的上下文是#1中的coroutineContext，很明显，子协程它可以有自己的上下文，两上下文可以进行combined，这里没有的添加调度器Dispatchers.Default，所以线程也还是主线程。coroutineContext + context 上下文能相加，用的就是重载plus操作符。
//from CoroutineContext
public operator fun plus(context: CoroutineContext): CoroutineContext =
......
CoroutineContext还支持coroutineContext[Job]，就用到了get约定，重载get运算符。
//from CoroutineContext
public operator fun <E : Element> get(key: Key<E>): E?
coroutineContext[Job]中的key是伴生对象，既然是伴生对象，那就是个final修饰的静态对象，协程上下文类的多个对象可以共享这个key，值会不会覆盖呢？
public interface ContinuationInterceptor : CoroutineContext.Element
companion object Key : CoroutineContext.Key<ContinuationInterceptor>
协程调度器、协程拦截器、协程拦截器都是协程上下文，都实现了CoroutineContext.Element。
3.1、从协程编译后的产物发现它的本体
在runBlocking中启动两个子协程，子协程共用一个线程。👇
使用show kotlin bytecode转换后的代码👇
public final class TestKt
public static final void main()
BuildersKt.runBlocking((CoroutineContext)(new CoroutineName("coroutine#1")), (Function2)(new Function2((Continuation)null)
int label;
@Nullable
public final Object invokeSuspend(@NotNull Object var1)
Object var6 = IntrinsicsKt.getCOROUTINE_SUSPENDED();
switch(this.label)
case 0:
ResultKt.throwOnFailure(var1);
System.out.println("1 " + Thread.currentThread().name + "---" + coroutineContext[CoroutineName])
ExecutorCoroutineDispatcher dispatcher = ThreadPoolDispatcherKt.newSingleThreadContext("my owner Thread ");
BuildersKt.launch$default($this$runBlocking, (new CoroutineName("coroutine#2")).plus((CoroutineContext)dispatcher), (CoroutineStart)null, (Function2)(new Function2((Continuation)null)
int label;
@Nullable
public final Object invokeSuspend(@NotNull Object $result)
Object var5 = IntrinsicsKt.getCOROUTINE_SUSPENDED();
switch(this.label)
case 0:
ResultKt.throwOnFailure($result);
System.out.println("2 " + Thread.currentThread().name + "---" + coroutineContext[CoroutineName])
this.label = 1;
if (DelayKt.delay(1000L, this) == var5)
return var5;
break;
case 1:
ResultKt.throwOnFailure($result);
break;
default:
throw new IllegalStateException("call to 'resume' before 'invoke' with coroutine");
System.out.println("3 " + Thread.currentThread().name + "---" + coroutineContext[CoroutineName])
return Unit.INSTANCE;
@NotNull
public final Continuation create(@Nullable Object value, @NotNull Continuation completion)
Intrinsics.checkNotNullParameter(completion, "completion");
Function2 var3 = new <anonymous constructor>(completion);
var3.L$0 = value;
return var3;
public final Object invoke(Object var1, Object var2)
return ((<undefinedtype>)this.create(var1, (Continuation)var2)).invokeSuspend(Unit.INSTANCE);
), 2, (Object)null);
BuildersKt.launch$default($this$runBlocking, (new CoroutineName("coroutine#2")).plus((CoroutineContext)dispatcher), (CoroutineStart)null, (Function2)(new Function2((Continuation)null)
int label;
@Nullable
public final Object invokeSuspend(@NotNull Object $result)
Object var5 = IntrinsicsKt.getCOROUTINE_SUSPENDED();
switch(this.label)
case 0:
ResultKt.throwOnFailure($result);
System.out.println("21 " + Thread.currentThread().name + "---" + coroutineContext[CoroutineName])
this.label = 1;
if (DelayKt.delay(500L, this) == var5)
return var5;
break;
case 1:
ResultKt.throwOnFailure($result);
break;
default:
throw new IllegalStateException("call to 'resume' before 'invoke' with coroutine");
System.out.println("31 " + Thread.currentThread().name + "---" + coroutineContext[CoroutineName])
return Unit.INSTANCE;
@NotNull
public final Continuation create(@Nullable Object value, @NotNull Continuation completion)
Intrinsics.checkNotNullParameter(completion, "completion");
Function2 var3 = new <anonymous constructor>(completion);
var3.L$0 = value;
return var3;
public final Object invoke(Object var1, Object var2)
return ((<undefinedtype>)this.create(var1, (Continuation)var2)).invokeSuspend(Unit.INSTANCE);
), 2, (Object)null);
System.out.println("4 " + Thread.currentThread().name + "---" + coroutineContext[CoroutineName])
return Unit.INSTANCE;
default:
throw new IllegalStateException("call to 'resume' before 'invoke' with coroutine");
@NotNull
public final Continuation create(@Nullable Object value, @NotNull Continuation completion)
Intrinsics.checkNotNullParameter(completion, "completion");
Function2 var3 = new <anonymous constructor>(completion);
var3.L$0 = value;
return var3;
public final Object invoke(Object var1, Object var2)
return ((<undefinedtype>)this.create(var1, (Continuation)var2)).invokeSuspend(Unit.INSTANCE);
));
public static void main(String[] var0)
main();
想不到协程的bytecode也会存在回调嵌套，这里还只是父协程嵌套两个子协程，如果存在多个协程嵌套，层级多的话，那将也存在回调地狱。
协程能够挂起的本质，其实就是协程体的代码被挂起点一分为二，这里delay是挂起函数，那代码就分为协程体开始到挂起点delay，delay后面到结束，前面的代码走switch的case 0的逻辑，后面的代码就是挂起点恢复之后，再次走下case 1以及后面的代码。
注意调用挂起函数，不一定会真正挂起，具体看返回值是不是IntrinsicsKt.getCOROUTINE_SUSPENDED();，是的就直接return了，下次需再次调用invokeSuspend，就会走label==1了，执行后面的逻辑。
单拎出一个子协程看看：
BuildersKt.launch$default($this$runBlocking, (new CoroutineName("coroutine#2")).plus((CoroutineContext)dispatcher), (CoroutineStart)null, (Function2)(new Function2((Continuation)null)
int label;
@Nullable
public final Object invokeSuspend(@NotNull Object $result) #2 这个是能找到的
Object var5 = IntrinsicsKt.getCOROUTINE_SUSPENDED();
switch(this.label)
case 0:
ResultKt.throwOnFailure($result);
System.out.println("2 " + Thread.currentThread().name + "---" + coroutineContext[CoroutineName])
this.label = 1;
if (DelayKt.delay(1000L, this) == var5)
return var5;
break;
case 1:
ResultKt.throwOnFailure($result);
break;
default:
throw new IllegalStateException("call to 'resume' before 'invoke' with coroutine");
System.out.println("3 " + Thread.currentThread().name + "---" + coroutineContext[CoroutineName])
return Unit.INSTANCE;
@NotNull
public final Continuation create(@Nullable Object value, @NotNull Continuation completion)
Intrinsics.checkNotNullParameter(completion, "completion");
Function2 var3 = new <anonymous constructor>(completion);
var3.L$0 = value;
return var3;
public final Object invoke(Object var1, Object var2) #1 这里的调用没有找到
return ((<undefinedtype>)this.create(var1, (Continuation)var2)).invokeSuspend(Unit.INSTANCE);
), 2, (Object)null);
首先invoke() #1是怎么触发的？没有找到对应的调用地方，有小伙伴找到的话，麻烦告知下。
再次调用invokeSuspend #2是怎么触发的？ 是在continuation.resumeWith(xxx)时触发。
众所周知，kotlin的suspend方法编译之后会在最后一个参数的位置放上Continuation<T>。
public fun CoroutineScope.launch(context: CoroutineContext = EmptyCoroutineContext,
start: CoroutineStart = CoroutineStart.DEFAULT,
block: suspend CoroutineScope.() -> Unit): Job
BuildersKt.launch$default($this$runBlocking,
(new CoroutineName("coroutine#2")).plus((CoroutineContext)dispatcher),
(CoroutineStart)null, (Function2)(new Function2((Continuation)null) ),2, (Object)null);
对应看下，CoroutineScope的launch拓展函数，在java调用时就是作为第一个参数传入，第二个参数就是协程上下文，第三个参数是协程启动模式，接下来为一个就是Function2的匿名类对象，接收参数是Continuation类型，最后多出的两个参数是2和(Object)null，这两个参数是啥，暂不清楚。
当查看原始字节码时，可以看到以下声明：
final class com/docwei/kotlindemo/TestKt$main$1$1
extends kotlin/coroutines/jvm/internal/SuspendLambda //协程体编译成了SuspendLambda类！！！！
implements kotlin/jvm/functions/Function2 //同时也是Fucntion2！！！
INVOKESTATIC kotlinx/coroutines/BuildersKt.launch$default
(Lkotlinx/coroutines/CoroutineScope;
Lkotlin/coroutines/CoroutineContext;
Lkotlinx/coroutines/CoroutineStart;
Lkotlin/jvm/functions/Function2;
ILjava/lang/Object;)Lkotlinx/coroutines/Job;
SuspendLambda类 可以看下类继承关系
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) //#1
return coroutine
1看起来是我们创建了一个新协程，然后传入block就是我们的协程体。
//from AbstractCoroutine
public fun <R> start(start: CoroutineStart, receiver: R, block: suspend R.以上是关于浅析kotlin协程launch delay调用的主要内容，如果未能解决你的问题，请参考以下文章