Kotlin Job啟動流程原始碼層深入分析

private fun testParentChildJob() {
    val coroutineContext = Job() + CoroutineName("name1") + Dispatchers.IO + CoroutineExceptionHandler{ c,e -> println(e.message) }
    val myScope = CoroutineScope(coroutineContext)
    val job = myScope.launch {
        println("myScope.launch :")
    }
}

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
}

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
}

private open class StandaloneCoroutine(
    parentContext: CoroutineContext,
    active: Boolean
) : AbstractCoroutine<Unit>(parentContext, active) {
	//省略。。。
}
public abstract class AbstractCoroutine<in T>(
    /**
     * The context of the parent coroutine.
     */
    @JvmField
    protected val parentContext: CoroutineContext,
    active: Boolean = true
) : JobSupport(active), Job, Continuation<T>, CoroutineScope {
    /**
     * The context of this coroutine that includes this coroutine as a [Job].
     */
    @Suppress("LeakingThis")
    public final override val context: CoroutineContext = parentContext + this
    /**
     * The context of this scope which is the same as the [context] of this coroutine.
     */
    public override val coroutineContext: CoroutineContext get() = context
    override val isActive: Boolean get() = super.isActive
}

    public fun <R> start(start: CoroutineStart, receiver: R, block: suspend R.() -> T) {
        initParentJob()
        start(block, receiver, this)
    }

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
    }

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> {
        //省略。。。
        createCoroutineFromSuspendFunction(probeCompletion) {
            (this as Function1<Continuation<T>, Any?>).invoke(it)
        }
}
private inline fun <T> createCoroutineFromSuspendFunction(
    completion: Continuation<T>,
    crossinline block: (Continuation<T>) -> Any?
): Continuation<Unit> {
    val context = completion.context
    // label == 0 when coroutine is not started yet (initially) or label == 1 when it was
    return if (context === EmptyCoroutineContext)
		//省略。。。
    else
        object : ContinuationImpl(completion as Continuation<Any?>, context) {
            private var label = 0
            override fun invokeSuspend(result: Result<Any?>): Any? =
                when (label) {
                    0 -> {
                        label = 1
                        result.getOrThrow() // Rethrow exception if trying to start with exception (will be caught by BaseContinuationImpl.resumeWith
                        block(this) // run the block, may return or suspend
                    }
                	//省略。。。
                }
        }
}

public fun <T> Continuation<T>.resumeCancellableWith(result: Result<T>): Unit = when (this) {
    is DispatchedContinuation -> resumeCancellableWith(result)
    else -> resumeWith(result)
}
//DispatchedContinuation extends DIspatchedTask
inline fun resumeCancellableWith(result: Result<T>) {
    val state = result.toState()
    if (dispatcher.isDispatchNeeded(context)) {
        _state = state
        resumeMode = MODE_CANCELLABLE
        dispatcher.dispatch(context, this)
    } else {
        省略。。。
    }
}
//DIspatchedTask
public final override fun run() {
        val taskContext = this.taskContext
        var fatalException: Throwable? = null
        try {
            val delegate = delegate as DispatchedContinuation<T>
            val continuation = delegate.continuation
            withCoroutineContext(context, delegate.countOrElement) {
            	//省略。。。
                if (exception == null && job != null && !job.isActive) {
                    //省略。。。
                } else {
                    if (exception != null) continuation.resumeWithException(exception)
                    else continuation.resume(getSuccessfulResult(state))
                }
            }
        } catch (e: Throwable) {
            //省略。。。
        }
    }

internal class DispatchedContinuation<in T>(
    @JvmField val dispatcher: CoroutineDispatcher,
    @JvmField val continuation: Continuation<T>
) : DispatchedTask<T>(MODE_ATOMIC_DEFAULT), CoroutineStackFrame, Continuation<T> by continuation {
	//省略。。。
    override val delegate: Continuation<T>
        get() = this

	//省略。。。
}
//Continuation
public inline fun <T> Continuation<T>.resume(value: T): Unit =
    resumeWith(Result.success(value))

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 param = result
        while (true) {
            //省略。。。
            with(current) {
           		try {
                    val outcome = invokeSuspend(param)
                    if (outcome === COROUTINE_SUSPENDED) return
                    Result.success(outcome)
                } catch (exception: Throwable) {
                    Result.failure(exception)
                }
                //省略。。。
                releaseIntercepted() // this state machine instance is terminating
                if (completion is BaseContinuationImpl) {
                    //省略。。。
                } else {
                    // top-level completion reached -- invoke and return
                    completion.resumeWith(outcome)
                    return
                }
            }
        }
    }

//AbstractCoroutine
internal fun initParentJob() {
	//取出上下文集合中的Job元素，呼叫initParentJobInternal方法
	initParentJobInternal(parentContext[Job])
}
//AbstractCoroutine
internal fun initParentJobInternal(parent: Job?) {
	//省略。。。
	parent.start() // make sure the parent is started
	//省略。。。
	val handle = parent.attachChild(this)
	parentHandle = handle
	//省略。。。
	if (isCompleted) {
	    handle.dispose()
	}
}

//JobSupport
public final override fun attachChild(child: ChildJob): ChildHandle {
    /*
     * Note: This function attaches a special ChildHandleNode node object. This node object
     * is handled in a special way on completion on the coroutine (we wait for all of them) and
     * is handled specially by invokeOnCompletion itself -- it adds this node to the list even
     * if the job is already cancelling. For cancelling state child is attached under state lock.
     * It's required to properly wait all children before completion and provide linearizable hierarchy view:
     * If child is attached when the job is already being cancelled, such child will receive immediate notification on
     * cancellation, but parent *will* wait for that child before completion and will handle its exception.
     */
    return invokeOnCompletion(onCancelling = true, handler = ChildHandleNode(this, child).asHandler) as ChildHandle
}
//JobSupport
internal class ChildHandleNode(
    parent: JobSupport,
    @JvmField val childJob: ChildJob
) : JobCancellingNode<JobSupport>(parent), ChildHandle {
    override fun invoke(cause: Throwable?) = childJob.parentCancelled(job)
    override fun childCancelled(cause: Throwable): Boolean = job.childCancelled(cause)
    override fun toString(): String = "ChildHandle[$childJob]"
}

//JobSupport
public final override fun invokeOnCompletion(
        onCancelling: Boolean,
        invokeImmediately: Boolean,
        handler: CompletionHandler
    ): DisposableHandle {
        var nodeCache: JobNode<*>? = null
        loopOnState { state ->
            when (state) {
                is Empty -> { // EMPTY_X state -- no completion handlers
                    if (state.isActive) {
                        // try move to SINGLE state
                        val node = nodeCache ?: makeNode(handler, onCancelling).also { nodeCache = it }
                        if (_state.compareAndSet(state, node)) return node
                    }
                    //省略。。。
                }
                is Incomplete -> {
                    val list = state.list
                    if (list == null) { // SINGLE/SINGLE+
                        promoteSingleToNodeList(state as JobNode<*>)
                    } else {
                        var rootCause: Throwable? = null
                        var handle: DisposableHandle = NonDisposableHandle
                      	val node = nodeCache ?: makeNode(handler, onCancelling).also { nodeCache = it }
                        if (!addLastAtomic(state, list, node)) return@loopOnState // retry
                        if (rootCause == null) return node
                  	 	 //省略。。。
                        if (rootCause != null) {
                            //省略。。。
                        } else {
                            val node = nodeCache ?: makeNode(handler, onCancelling).also { nodeCache = it }
                            if (addLastAtomic(state, list, node)) return node
                        }
                    }
                }
                else -> { // is complete
                   //省略。。。
                }
            }
        }
    }

override fun childCancelled(cause: Throwable): Boolean = job.childCancelled(cause)

override fun invoke(cause: Throwable?) = childJob.parentCancelled(job)