我们从最基本的launch用法源码进行分析,带大家走完下面示例的整个流程
这篇文章主要代大家走一遍launch方法的流程
这是根示例,下面说的根示例都是它
GlobalScope.launch {
print("launch用法")
delay(1000)
}
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一、直接进入launch查看源码:
public fun CoroutineScope.launch(
context: CoroutineContext = EmptyCoroutineContext,
start: CoroutineStart = CoroutineStart.DEFAULT,
block: suspend CoroutineScope.() -> Unit
): Job {
//1-将当前协程作用域的context,与已有的结合起来返回一个新的
val newContext = newCoroutineContext(context)
//2-创建一个新的协程
val coroutine = if (start.isLazy)
LazyStandaloneCoroutine(newContext, block) else
StandaloneCoroutine(newContext, active = true)
//3-执行协程
coroutine.start(start, coroutine, block)
return coroutine
}
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1.1、第一步 先看newCoroutineContext方法
关于一些基础用法不太了解的可以看看这篇文章:juejin.cn/post/695061…
///将当前协程作用域的context,与已有的结合起来返回一个新的
@ExperimentalCoroutinesApi
public actual fun CoroutineScope.newCoroutineContext(context: CoroutineContext): CoroutineContext {
val combined = coroutineContext + context
val debug = if (DEBUG) combined + CoroutineId(COROUTINE_ID.incrementAndGet()) else combined
return if (combined !== Dispatchers.Default && combined[ContinuationInterceptor] == null)
debug + Dispatchers.Default else debug
}
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1.2、第二步看if条件语句,因为默认是CoroutineStart.DEFAULT所以,创建的是StandaloneCoroutine
------------------它的传递的泛型是 unit类型,注意后续会用到该泛型
///详细如下--它的主要实现是在AbstractCoroutine中
private open class StandaloneCoroutine(
parentContext: CoroutineContext,
active: Boolean
) : AbstractCoroutine<Unit>(parentContext, initParentJob = true, active = active) {
override fun handleJobException(exception: Throwable): Boolean {
handleCoroutineException(context, exception)
return true
}
}
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AbstractCoroutine的代码如下,主要看他的继承与抽象接口,后续泛型可用到(比如:CoroutineScope对象等)
public abstract class AbstractCoroutine<in T>(
parentContext: CoroutineContext,
initParentJob: Boolean,
active: Boolean
) : JobSupport(active), Job, Continuation<T>, CoroutineScope {
......省略n多代码
}
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1.3、到了第三步coroutine.start(start, coroutine, block)方法,
参数含义: 1. - start的值为 CoroutineStart.DEFAULT它是协程的一直生效方式 1. - coroutine为上面第二步时创建的协程对象 1. - block的类型是一个CoroutineScope对象的扩展方法,它的返回可以是任意值(个人认为 关键所在,在我们这次分析中它对应,示例中的方法块)
二、分析上面的协程开始方法 coroutine.start(start, coroutine, block)
根据指向因为coroutine是StandaloneCoroutine对象它的start方法但是它没有所以是它的父类AbstractCoroutine中的:
public fun <R> start(start: CoroutineStart, receiver: R, block: suspend R.() -> T) {
///创建父协程工作
initParentJob()
///开启当前协程任务
start(block, receiver, this)
}
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需要注意的是:这里的start方法中的参数,注意观察与下面的不要被名称所误导
2.1、 initParentJob() 方法,///因为在 ·根示例· 中没有父协程,所以返回了
internal fun initParentJobInternal(parent: Job?) {
assert { parentHandle == null }
if (parent == null) {///因为在当前示例中没有父协程,所以返回了
parentHandle = NonDisposableHandle
return
}
parent.start() // make sure the parent is started
@Suppress("DEPRECATION")
val handle = parent.attachChild(this)
parentHandle = handle
// now check our state _after_ registering (see tryFinalizeSimpleState order of actions)
if (isCompleted) {
handle.dispose()
parentHandle = NonDisposableHandle // release it just in case, to aid GC
}
}
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2.2、因为在根示例中没有父协程,所以接下来直接看start(block, receiver, this)方法
2.2.1、start(block, receiver, this)方法这里的start对应第一个参数:start: CoroutineStart,...,它是kotlin的invoke的用法,不清楚 invoke用法的可以搜一下
public fun <R> start(:start: CoroutineStart,... receiver: R, block: suspend R.() -> T) {
initParentJob()
start(block, receiver, this)
}
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参数含义:
block参数变量中的R泛型,在这个根示例中,它代表了CoroutineScope 1. - start的值为 CoroutineStart.DEFAULT它是协程的一直生效方式 1. - receiver是上面的StandaloneCoroutine 1. - this的他指代当前的AbstractCoroutine对象,但是它的具体实现子类为StandaloneCoroutine
2.2.2、所以我们找到CoroutineStart类,查看里面的invoke方法,并且要找到带有三个参数的方法如下:
@InternalCoroutinesApi
public operator fun <R, T> invoke(block: suspend R.() -> T, receiver: R, completion: Continuation<T>): Unit =
when (this) {
DEFAULT -> block.startCoroutineCancellable(receiver, completion)
ATOMIC -> block.startCoroutine(receiver, completion)
UNDISPATCHED -> block.startCoroutineUndispatched(receiver, completion)
LAZY -> Unit // will start lazily
}
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参数含义: 1. - block为根示例的方法体 1. - receiver是上面的StandaloneCoroutine 1. - completion的他指代当前的AbstractCoroutine对象,他实现了Continuation,但是它的具体实现子类为StandaloneCoroutine
因为:
上面的when表达式,传入当前的CoroutineStart它自身,它是一个enum,它的值是:根据上面1.1示例中的CoroutineScope.launch(...)扩展方法得知它默认是 CoroutineStart.DEFAULT,所以上面代码when走的是 block.startCoroutineCancellable(receiver, completion)方法。
所以: 走的是下面2.2.3这一块代码,,他又是一个协程方法的扩展方法(该方法,可以看出是block的扩展,从根示例 代码 可以知道block就是我们想要执行的方法体)
2.2.3、 增加一个协程取消的监听,R是一个参数变量,在这个根示例中,它代表了CoroutineScope
internal fun <R, T> (suspend (R) -> T).startCoroutineCancellable(
receiver: R, completion: Continuation<T>,
onCancellation: ((cause: Throwable) -> Unit)? = null
) =
runSafely(completion) {
createCoroutineUnintercepted(receiver, completion).intercepted().resumeCancellableWith(Result.success(Unit), onCancellation)
}
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参数含义: 1. - receiver是上面的StandaloneCoroutine 1. - completion 但是它的具体实现子类为StandaloneCoroutine,而他是AbstractCoroutine的子类,它的类型 completion: Continuation,”泛型T“,由继承关系可知是 Unit 类型的
三、 createCoroutineUnintercepted方法,这个根据虚拟机生成不同的实现对象,截图如下
具体代码如下:T 泛型代表Unit,可以看作一个方法体,该协程的挂起 方法体 扩展了一个名为createCoroutineUnintercepted的方法
@SinceKotlin("1.3")
public actual fun <T> (suspend () -> T).createCoroutineUnintercepted(
completion: Continuation<T>
): Continuation<Unit> {
val probeCompletion = probeCoroutineCreated(completion) //1.可以看作一个空的拦截器
return if (this is BaseContinuationImpl)
create(probeCompletion)
else //
createCoroutineFromSuspendFunction(probeCompletion) {
(this as Function1<Continuation<T>, Any?>).invoke(it)
}
}
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3.1、上面代码其实是StandaloneCoroutine的扩展所以里面的if判断看看--StandaloneCoroutine是否实现过BaseContinuationImpl,结果没有找到该实现,后面查阅资料发现它是通过jvm实现的,在编译时生成的class文件,
我自己验证的话是通过debugg断点调试得出的结果,可以根据当前根示例的kotlin字节码的编译文件查看一些细节: 所以它走的是 create(probeCompletion)代码,它的具体实现,可以查看下面的反编译出的java文件,执行的是他的create方法
GlobalScope.launch {
print("launch用法")
delay(1000)
}
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上面这段代码,转化为Java如下,另取名称“java版根示例”,后面所说java版根示例都是,下面这一段代码:
BuildersKt.launch$default((CoroutineScope)GlobalScope.INSTANCE, (CoroutineContext)null, (CoroutineStart)null, (Function2)(new Function2((Continuation)null) {
int label;
@Nullable
public final Object invokeSuspend(@NotNull Object $result) {
Object var4 = IntrinsicsKt.getCOROUTINE_SUSPENDED();
switch(this.label) {
case 0:
ResultKt.throwOnFailure($result);
String var2 = "launch用法";
boolean var3 = false;
System.out.print(var2);
this.label = 1;
if (DelayKt.delay(1000L, this) == var4) {
return var4;
}
break;
case 1:
ResultKt.throwOnFailure($result);
break;
default:
throw new IllegalStateException("call to 'resume' before 'invoke' with coroutine");
}
return Unit.INSTANCE;
}
////首先执行到这里,返回一个Continuation类型的Function2,对象
@NotNull
public final Continuation create(@Nullable Object value, @NotNull Continuation completion) {
Intrinsics.checkNotNullParameter(completion, "completion");
Function2 var3 = new <anonymous constructor>(completion);
return var3;
}
public final Object invoke(Object var1, Object var2) {
return ((<undefinedtype>)this.create(var1, (Continuation)var2)).invokeSuspend(Unit.INSTANCE);
}
}), 3, (Object)null);
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3.2、协程方法体中的那一块内容的方法体是通过jvm实现的,我们可以通过反编译 jadx工具进行查看:
图一:
图二:
由图二可知他就是我们需要执行的东西,反编译出的:他执行的是
fun initKotlin(){
GlobalScope.launch {
print("launch用法")
delay(1000)
}
}
public final void initKotlin() {
BuildersKt__Builders_commonKt.launch$default(GlobalScope.INSTANCE, null, null, new MainActivity$initKotlin$1(null), 3, null);
}
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上面出现的位置是:new MainActivity 1(null), 3, null)对应上面字节码转化为的Java相关的Function2的位置,可看下图三
代码如下
final class MainActivity$initKotlin$1 extends SuspendLambda implements Function2<CoroutineScope, Continuation<? super Unit>, Object> {
int label;
MainActivity$initKotlin$1(Continuation<? super MainActivity$initKotlin$1> continuation) {
super(2, continuation);
}
public final Continuation<Unit> create(Object obj, Continuation<?> continuation) {
return new MainActivity$initKotlin$1<>(continuation);
}
public final Object invoke(CoroutineScope coroutineScope, Continuation<? super Unit> continuation) {
return ((MainActivity$initKotlin$1) create(coroutineScope, continuation)).invokeSuspend(Unit.INSTANCE);
}
public final Object invokeSuspend(Object $result) {
Object coroutine_suspended = IntrinsicsKt.getCOROUTINE_SUSPENDED();
switch (this.label) {
case 0:
ResultKt.throwOnFailure($result);
System.out.print("launch用法");
Continuation continuation = this;
this.label = 1;
if (DelayKt.delay(1000, continuation) != coroutine_suspended) {
break;
} else {
return coroutine_suspended;
}
case 1:
ResultKt.throwOnFailure($result);
break;
default:
throw new IllegalStateException("call to 'resume' before 'invoke' with coroutine");
}
return Unit.INSTANCE;
}
}
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由上图可知它实现了Function2的接口,所以,可以认为该根示例的作用域:它是实现了SuspendLambda,而SuspendLambda实现了BaseContinuationImpl接口,从这里我们知道了上面第上面的3.1、流程分析步骤没有错
3.3、create(probeCompletion)方法
上面3.1走的create方法,我们可以从上面分析,他走的invoke,最终调用invokeSuspend方法
3.4、 回到 3、步骤中的 createCoroutineUnintercepted 方法中的intercepted()
createCoroutineUnintercepted(receiver, completion).intercepted().resumeCancellableWith(Result.success(Unit), onCancellation)
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四、 根据流程继续走下去分析我们的SuspendLambda 根示例 中的intercepted()方法
该方法在 ContinuationImpl类中,他的具体实现从上面可知是SuspendLambda类,他们的代码如下:
4.1、、SuspendLambda.class:
internal abstract class SuspendLambda(
public override val arity: Int,
completion: Continuation<Any?>? ///StandaloneCoroutine
) : ContinuationImpl(completion), FunctionBase<Any?>, SuspendFunction {
constructor(arity: Int) : this(arity, null)
public override fun toString(): String =
if (completion == null)
Reflection.renderLambdaToString(this) // this is lambda
else
super.toString() // this is continuation
}
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解释:由create的发起方可知SuspendLambda的参数(completion: Continuation<Any?>)它的值是对应 create(receiver, probeCompletion)方法中的probeCompletion参数,追根溯源发现是StandaloneCoroutine对象。
4.2、、ContinuationImpl类如下:
// State machines for named suspend functions extend from this class
internal abstract class ContinuationImpl(
completion: Continuation<Any?>?,
private val _context: CoroutineContext?
) : BaseContinuationImpl(completion) {
constructor(completion: Continuation<Any?>?) : this(completion, completion?.context)
public override val context: CoroutineContext
get() = _context!!
**///在 三、 示例中3.4中 调用intercepted() 方法,就是这个函数**
@Transient
private var intercepted: Continuation<Any?>? = null
///默认会从协程上下文中取出 key为ContinuationInterceptor 的值
在这里取出的值就是上面newCoroutineContext创建的DefaultScheduler对象,它继承了CoroutineDispatcher,此处的 interceptContinuation 就是后者的函数
interceptContinuation 传入的参数是this,这个this就是示例代码中的匿名内部类(SuspendLambda),也就是最终需要分发执行的Continuation
public fun intercepted(): Continuation<Any?> =
intercepted
?: (context[ContinuationInterceptor]?.interceptContinuation(this) ?: this)
.also { intercepted = it }
protected override fun releaseIntercepted() {
val intercepted = intercepted
if (intercepted != null && intercepted !== this) {
context[ContinuationInterceptor]!!.releaseInterceptedContinuation(intercepted)
}
this.intercepted = CompletedContinuation // just in case
}
}
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解释: 默认会从协程上下文中取出 key为ContinuationInterceptor 的值在这里取出的值就是上面newCoroutineContext创建Dispatchers.Default对象,它是-》DefaultScheduler-》ExperimentalCoroutineDispatcher-》ExecutorCoroutineDispatcher-》CoroutineDispatcher 这样的继承关系,最终他调用的是interceptContinuation方法,他只在基类CoroutineDispatcher中实现了 CoroutineDispatcher对象,代码如下:细节查看下面 第五步骤 示例
public final override fun <T> interceptContinuation(continuation: Continuation<T>): Continuation<T> =
DispatchedContinuation(this, continuation)
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1. 所以此处的interceptContinuation 就是后者的函数interceptContinuation 传入的参数是this,这个this就是示例代码中的匿名内部类SuspendLambda,也就是最终需要分发执行的Continuation。
1. 而 (context[ContinuationInterceptor]?.interceptContinuation(this) ?: this)的interceptContinuation方法就是调用的CoroutineDispatcher对象中的
4.3、BaseContinuationImpl类如下:
@SinceKotlin("1.3")
internal abstract class BaseContinuationImpl(
// This is `public val` so that it is private on JVM and cannot be modified by untrusted code, yet
// it has a public getter (since even untrusted code is allowed to inspect its call stack).
public val completion: Continuation<Any?>?
) : Continuation<Any?>, CoroutineStackFrame, Serializable {
// This implementation is final. This fact is used to unroll resumeWith recursion.
public final override fun resumeWith(result: Result<Any?>) {
// This loop unrolls recursion in current.resumeWith(param) to make saner and shorter stack traces on resume
var current = this
var param = result
while (true) {
// Invoke "resume" debug probe on every resumed continuation, so that a debugging library infrastructure
// can precisely track what part of suspended callstack was already resumed
probeCoroutineResumed(current)
with(current) {
val completion = completion!! // fail fast when trying to resume continuation without completion
val outcome: Result<Any?> =
try {
val outcome = invokeSuspend(param)
if (outcome === COROUTINE_SUSPENDED) return
Result.success(outcome)
} catch (exception: Throwable) {
Result.failure(exception)
}
releaseIntercepted() // this state machine instance is terminating
if (completion is BaseContinuationImpl) {
// unrolling recursion via loop
current = completion
param = outcome
} else {
// top-level completion reached -- invoke and return
completion.resumeWith(outcome)
return
}
}
}
}
protected abstract fun invokeSuspend(result: Result<Any?>): Any?
protected open fun releaseIntercepted() {
// does nothing here, overridden in ContinuationImpl
}
public open fun create(completion: Continuation<*>): Continuation<Unit> {
throw UnsupportedOperationException("create(Continuation) has not been overridden")
}
public open fun create(value: Any?, completion: Continuation<*>): Continuation<Unit> {
throw UnsupportedOperationException("create(Any?;Continuation) has not been overridden")
}
public override fun toString(): String =
"Continuation at ${getStackTraceElement() ?: this::class.java.name}"
// --- CoroutineStackFrame implementation
public override val callerFrame: CoroutineStackFrame?
get() = completion as? CoroutineStackFrame
public override fun getStackTraceElement(): StackTraceElement? =
getStackTraceElementImpl()
}
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五、DispatchedContinuation类的实现过程:,找到了他也就完成了下面这段代码的intercepted部分
createCoroutineUnintercepted(receiver, completion).intercepted().resumeCancellableWith(Result.success(Unit), onCancellation)
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resumeCancellableWith的方法如下:
@InternalCoroutinesApi
public fun <T> Continuation<T>.resumeCancellableWith(
result: Result<T>,
onCancellation: ((cause: Throwable) -> Unit)? = null
): Unit = when (this) {
is DispatchedContinuation -> resumeCancellableWith(result, onCancellation)
else -> resumeWith(result)
}
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resumeCancellableWith这段代码走的是is DispatchedContinuation -> resumeCancellableWith(result, onCancellation) 大家可以debugg试试,前面4.2步骤 也给出了分析。
从上面可以后续就是resumeCancellableWith方法了,那就是DispatchedContinuation中的resumeCancellableWith方法
如下:
它继承DispatchedTask ->继承SchedulerTask() ->继承Task ->继承 Runable,可放入线程中去执行。 它继承了Continuation,并使用传进去的参数continuation赋值,所以DispatchedContinuation 也可以当做参数continuation 来使用
注意:这里的参数 @JvmField val continuation: Continuation<T> ,就是对应根示例的方法体
internal class DispatchedContinuation<in T>(
@JvmField val dispatcher: CoroutineDispatcher,
@JvmField val continuation: Continuation<T>
) : DispatchedTask<T>(MODE_UNINITIALIZED), CoroutineStackFrame, Continuation<T> by continuation {
.....省略若干
@Suppress("NOTHING_TO_INLINE")
inline fun resumeCancellableWith(
result: Result<T>,
noinline onCancellation: ((cause: Throwable) -> Unit)?
) {
val state = result.toState(onCancellation)
///dispatcher对应我们的前面 **4.2步骤** 分析得出的Dispatchers.Default+debug的对象
///dispatcher.isDispatchNeeded(context)对象就是Dispatchers.Default的isDispatchNeeded方法,他没有实现过重写,所以还是用的基类CoroutineDispatcher中的isDispatchNeeded方法,默认是true
if (dispatcher.isDispatchNeeded(context)) {
_state = state
resumeMode = MODE_CANCELLABLE
///这里的dispatcher,就是分发器DefaultScheduler对象
///在 **4.2步骤** 中分析出了this 对象他就是我们的SuspendLambda对象,也就是我们的根示例
dispatcher.dispatch(context, this)
} else {
executeUnconfined(state, MODE_CANCELLABLE) {
if (!resumeCancelled(state)) {
resumeUndispatchedWith(result)
}
}
}
}
}
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解释:
这里使用分发器,分发任务,你可能会有疑问,为什么不直接去执行,还要去分发后,再去执行呢? 不同的任务,处理的方式不同,例如更新UI的需要在主线程。分发器的功能 是把 任务分给 线程池(默认、IO) 或 Handler(通过handler post 发送任务到主线程)。
在第2步,向 协程上下文CoroutineContext 中 加入了一个默认分发器Dispatchers.Default
5.1、在看DefaultScheduler对象的 dispatcher.dispatch(context, this)过程:也可以说是 根示例 的执行模块
在 4.2步骤 中分析出了它的继承过程如下,它是-》DefaultScheduler-》 ExperimentalCoroutineDispatcher-》ExecutorCoroutineDispatcher-》CoroutineDispatcher 这样的继承关系,它的dispatcher方法在类 ExperimentalCoroutineDispatcher 中实现 可以看出是通过线程池分发处理
@InternalCoroutinesApi
public open class ExperimentalCoroutineDispatcher(
private val corePoolSize: Int,
private val maxPoolSize: Int,
private val idleWorkerKeepAliveNs: Long,
private val schedulerName: String = "CoroutineScheduler"
) : ExecutorCoroutineDispatcher() {
public constructor(
corePoolSize: Int = CORE_POOL_SIZE,
maxPoolSize: Int = MAX_POOL_SIZE,
schedulerName: String = DEFAULT_SCHEDULER_NAME
) : this(corePoolSize, maxPoolSize, IDLE_WORKER_KEEP_ALIVE_NS, schedulerName)
@Deprecated(message = "Binary compatibility for Ktor 1.0-beta", level = DeprecationLevel.HIDDEN)
public constructor(
corePoolSize: Int = CORE_POOL_SIZE,
maxPoolSize: Int = MAX_POOL_SIZE
) : this(corePoolSize, maxPoolSize, IDLE_WORKER_KEEP_ALIVE_NS)
override val executor: Executor
get() = coroutineScheduler
// This is variable for test purposes, so that we can reinitialize from clean state
private var coroutineScheduler = createScheduler()
override fun dispatch(context: CoroutineContext, block: Runnable): Unit =
try {
coroutineScheduler.dispatch(block)
} catch (e: RejectedExecutionException) {
// CoroutineScheduler only rejects execution when it is being closed and this behavior is reserved
// for testing purposes, so we don't have to worry about cancelling the affected Job here.
DefaultExecutor.dispatch(context, block)
}
....
private fun createScheduler() = CoroutineScheduler(corePoolSize, maxPoolSize, idleWorkerKeepAliveNs, schedulerName)
### ....省略若干
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从上面这段代码可知我们是通过线程池进行挂起函数处理。它是CoroutineScheduler对象的dispatch方法
六、* CoroutineScheduler对象,线程池的分发:
6.1、CoroutineScheduler 是一个协程调度器,使用共享的线程,每个线程就是一个worker。需要执行的协程任务,会被添加到队列中,队列分为worker本地队列和全局队列。worker的本地队列为空的时候,会从其它worker拿来协程任务去执行。
源码分析到这里,后面的流程,应该你也能猜个大概,业务功能,分发器,协程调度类都有了。 这里先从整体上,看一下后续的流程
DispatchedContinuation对象,间接继承了 Runable和直接继承了Continuation类型。所以可得知以下两点
1. 此时业务代码(示例中的匿名内部类 Continuation 类型的),已经被封装成了DispatchedContinuation类型,可通过变量delegate,来获取此Continuation 类型。
1. 因为该对象是Runable类型,所以可在线程中运行协程调度类,主要有这三个工作,1、根据DispatchedContinuation创建任务、2、创建线程,3、执行任务。
1. 在DispatchedContinuation对象的run 函数中,会执行 示例中的匿名内部类 的resumeWith() ->invokeSuspend()。
///6.1、参数block我们的** 根示例 **内容对象
fun dispatch(block: Runnable, taskContext: TaskContext = NonBlockingContext, tailDispatch: Boolean = false) {
///6.2、
trackTask() // this is needed for virtual time support
///6.3、使用DispatchedContinuation 创建任务,最终在线程中执行这个任务
val task = createTask(block, taskContext)
// try to submit the task to the local queue and act depending on the result
///6.4、一个worker 就是一个线程,这里尝试把任务加入到worker 的本地队列中
val currentWorker = currentWorker()
val notAdded = currentWorker.submitToLocalQueue(task, tailDispatch)
if (notAdded != null) {
///6.5、如果本地队列添加失败,就加入到全局队列
if (!addToGlobalQueue(notAdded)) {
// Global queue is closed in the last step of close/shutdown -- no more tasks should be accepted
throw RejectedExecutionException("$schedulerName was terminated")
}
}
val skipUnpark = tailDispatch && currentWorker != null
// Checking 'task' instead of 'notAdded' is completely okay
if (task.mode == TASK_NON_BLOCKING) {
if (skipUnpark) return
///6.6、在本例中,会执行这句函数,创建线程,执行任务
signalCpuWork()
} else {
// Increment blocking tasks anyway
signalBlockingWork(skipUnpark = skipUnpark)
}
}
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6.2、 signalCpuWork()方法
//从这个函数的名称,就能看出 是单个work
fun signalCpuWork() {
// 尝试获取一个可用的worker,如果获取到了,就直接返回,因为任务已经加入队列中,后面被执行
if (tryUnpark()) return
//如果没有获取到,就创建一个新的worker,并start
if (tryCreateWorker()) return
tryUnpark()
}
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6.3、tryCreateWorker(),看看创建新的worker任务
6.3.1、tryCreateWorker()
private fun tryCreateWorker(state: Long = controlState.value): Boolean {
val created = createdWorkers(state)
val blocking = blockingTasks(state)
val cpuWorkers = (created - blocking).coerceAtLeast(0)
/*
* We check how many threads are there to handle non-blocking work,
* and create one more if we have not enough of them.
*/
if (cpuWorkers < corePoolSize) {
val newCpuWorkers = createNewWorker()
// If we've created the first cpu worker and corePoolSize > 1 then create
// one more (second) cpu worker, so that stealing between them is operational
if (newCpuWorkers == 1 && corePoolSize > 1) createNewWorker()
if (newCpuWorkers > 0) return true
}
return false
}
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6.3.2、createNewWorker():小于核心线程数创建一个新的
private fun createNewWorker(): Int {
synchronized(workers) {
// Make sure we're not trying to resurrect terminated scheduler
if (isTerminated) return -1
val state = controlState.value
val created = createdWorkers(state)
val blocking = blockingTasks(state)
val cpuWorkers = (created - blocking).coerceAtLeast(0)
// Double check for overprovision
if (cpuWorkers >= corePoolSize) return 0
if (created >= maxPoolSize) return 0
// start & register new worker, commit index only after successful creation
val newIndex = createdWorkers + 1
require(newIndex > 0 && workers[newIndex] == null)
/*
* 1) Claim the slot (under a lock) by the newly created worker
* 2) Make it observable by increment created workers count
* 3) Only then start the worker, otherwise it may miss its own creation
*/
val worker = Worker(newIndex)
workers[newIndex] = worker
require(newIndex == incrementCreatedWorkers())
worker.start()
return cpuWorkers + 1
}
}
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上面的关键点在于worker.start()方法,很明显开始执行工作
6.4、internal inner class Worker private constructor() : Thread() {}类的在上面被开启,下面看看它的执行:
internal inner class Worker private constructor() : Thread() {
...
override fun run() = runWorker()
private fun runWorker() {
var rescanned = false
while (!isTerminated && state != WorkerState.TERMINATED) {
/// 从队列中 取出第一个任务,参数表示是否从本地队列中查找
val task = findTask(mayHaveLocalTasks)
// Task found. Execute and repeat
if (task != null) {
rescanned = false
minDelayUntilStealableTaskNs = 0L
//重点是这里,执行任务
executeTask(task)
continue
} else {
mayHaveLocalTasks = false
}
/*
* No tasks were found:
* 1) Either at least one of the workers has stealable task in its FIFO-buffer with a stealing deadline.
* Then its deadline is stored in [minDelayUntilStealableTask]
*
* Then just park for that duration (ditto re-scanning).
* While it could potentially lead to short (up to WORK_STEALING_TIME_RESOLUTION_NS ns) starvations,
* excess unparks and managing "one unpark per signalling" invariant become unfeasible, instead we are going to resolve
* it with "spinning via scans" mechanism.
* NB: this short potential parking does not interfere with `tryUnpark`
*/
if (minDelayUntilStealableTaskNs != 0L) {
if (!rescanned) {
rescanned = true
} else {
rescanned = false
tryReleaseCpu(WorkerState.PARKING)
interrupted()
LockSupport.parkNanos(minDelayUntilStealableTaskNs)
minDelayUntilStealableTaskNs = 0L
}
continue
}
/*
* 2) Or no tasks available, time to park and, potentially, shut down the thread.
* Add itself to the stack of parked workers, re-scans all the queues
* to avoid missing wake-up (requestCpuWorker) and either starts executing discovered tasks or parks itself awaiting for new tasks.
*/
tryPark()
}
tryReleaseCpu(WorkerState.TERMINATED)
}
private fun executeTask(task: Task) {
val taskMode = task.mode
idleReset(taskMode)
beforeTask(taskMode)
runSafely(task)
afterTask(taskMode)
}
///最终执行到了这里
fun runSafely(task: Task) {
try {
task.run()
} catch (e: Throwable) {
val thread = Thread.currentThread()
thread.uncaughtExceptionHandler.uncaughtException(thread, e)
} finally {
unTrackTask()
}
}
...
}
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Worker继承了Thread所以关键在于 override fun run() = runWorker()-》executeTask(task: Task)-》 runSafely(task: Task) 最终执行了 task.run()方法
还记得我们在4.1中它的实现分发器是DispatchedContinuation类,而他的run方法来自于他继承的 DispatchedTask类,所以最终执行DispatchedTask类的run方法:
6.5、DispatchedTask的run方法
public final override fun run() {
assert { resumeMode != MODE_UNINITIALIZED } // should have been set before dispatching
val taskContext = this.taskContext
var fatalException: Throwable? = null
try {
---------- //1.该参数在DispatchedContinuation 类中被复写,赋值为this,所以这里可以当做DispatchedContinuation类型
val delegate = delegate as DispatchedContinuation<T>
------------- //2.在创建DispatchedContinuation 的时候,传入的了两个参数(第8步),其中continuation 就是业务中的匿名内部类
val continuation = delegate.continuation
withContinuationContext(continuation, delegate.countOrElement) {
val context = continuation.context
val state = takeState() // NOTE: Must take state in any case, even if cancelled
val exception = getExceptionalResult(state)
/*
* Check whether continuation was originally resumed with an exception.
* If so, it dominates cancellation, otherwise the original exception
* will be silently lost.
*/
val job = if (exception == null && resumeMode.isCancellableMode) context[Job] else null
if (job != null && !job.isActive) {
val cause = job.getCancellationException()
cancelCompletedResult(state, cause)
continuation.resumeWithStackTrace(cause)
} else {
if (exception != null) {
continuation.resumeWithException(exception)
} else {
----------------//3.到这里,continuation 就是业务中的内部类了
continuation.resume(getSuccessfulResult(state))
}
}
}
} catch (e: Throwable) {
// This instead of runCatching to have nicer stacktrace and debug experience
fatalException = e
} finally {
val result = runCatching { taskContext.afterTask() }
handleFatalException(fatalException, result.exceptionOrNull())
}
}
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上面 continuation.resume(getSuccessfulResult(state)) 这一块点击关系链最终是调用了 Continuation 的resumeWith(Result.success(value))方法: 又因为我们上面分析得出根示例的方法体它的结构是:
SuspendLambda-》ContinuationImpl-》BaseContinuationImpl
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所以最终调用它的resumeWith:如下
public final override fun resumeWith(result: Result<Any?>) {
// This loop unrolls recursion in current.resumeWith(param) to make saner and shorter stack traces on resume
var current = this
var param = result
while (true) {
// Invoke "resume" debug probe on every resumed continuation, so that a debugging library infrastructure
// can precisely track what part of suspended callstack was already resumed
probeCoroutineResumed(current)
with(current) {
val completion = completion!! // fail fast when trying to resume continuation without completion
val outcome: Result<Any?> =
try {
val outcome = invokeSuspend(param)
if (outcome === COROUTINE_SUSPENDED) return
Result.success(outcome)
} catch (exception: Throwable) {
Result.failure(exception)
}
releaseIntercepted() // this state machine instance is terminating
if (completion is BaseContinuationImpl) {
// unrolling recursion via loop
current = completion
param = outcome
} else {
// top-level completion reached -- invoke and return
completion.resumeWith(outcome)
return
}
}
}
}
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上面的话就是调用 **invokeSuspend(result: Result<Any?>): Any?**流程,到这里整个调用流程就分析完成了
参考: blog.csdn.net/xx326664162… juejin.cn/post/695061… blog.csdn.net/xx326664162…