public actual object Dispatchers {
    @JvmStatic
    public actual val Default: CoroutineDispatcher = DefaultScheduler
    @JvmStatic
    public actual val Main: MainCoroutineDispatcher get() = MainDispatcherLoader.dispatcher
    @JvmStatic
    public actual val Unconfined: CoroutineDispatcher = kotlinx.coroutines.Unconfined
    @JvmStatic
    public val IO: CoroutineDispatcher = DefaultIoScheduler
}
public abstract class CoroutineDispatcher :
    AbstractCoroutineContextElement(ContinuationInterceptor), ContinuationInterceptor {
}
public interface ContinuationInterceptor : CoroutineContext.Element {}
public interface Element : CoroutineContext {}

fun main() {
    val coroutineScope = CoroutineScope(Job())
    coroutineScope.launch {
        println("Thread : ${Thread.currentThread().name}")
    }
    Thread.sleep(5000L)
}

public fun CoroutineScope.launch(
    context: CoroutineContext = EmptyCoroutineContext,
    start: CoroutineStart = CoroutineStart.DEFAULT,
    block: suspend CoroutineScope.() -> Unit
): Job {
    //代碼1
    val newContext = newCoroutineContext(context)
    //代碼2
    val coroutine = if (start.isLazy)
        LazyStandaloneCoroutine(newContext, block) else
        StandaloneCoroutine(newContext, active = true)
    //代碼3
    coroutine.start(start, coroutine, block)
    return coroutine
}

public actual fun CoroutineScope.newCoroutineContext(context: CoroutineContext): CoroutineContext {
    //從父協(xié)程那里繼承過(guò)來(lái)的context+這次的context
    val combined = coroutineContext.foldCopiesForChildCoroutine() + context
    val debug = if (DEBUG) combined + CoroutineId(COROUTINE_ID.incrementAndGet()) else combined
    //combined可以簡(jiǎn)單的把它看成是一個(gè)map，它是CoroutineContext類型的
    //如果當(dāng)前context不等于Dispatchers.Default，而且從map里面取ContinuationInterceptor（用于攔截之后分發(fā)線程的）值為空，說(shuō)明沒(méi)有傳入?yún)f(xié)程應(yīng)該在哪個(gè)線程上運(yùn)行的相關(guān)參數(shù)
    return if (combined !== Dispatchers.Default && combined[ContinuationInterceptor] == null)
        debug + Dispatchers.Default else debug
}

public interface CoroutineContext {
     /**
     * Returns the element with the given [key] from this context or `null`.
     */
    public operator fun <E : Element> get(key: Key<E>): E?
     /**
     * Returns a context containing elements from this context and elements from  other [context].
     * The elements from this context with the same key as in the other one are dropped.
     */
    public operator fun plus(context: CoroutineContext): CoroutineContext {
        ......
    }
}

public fun <T> (suspend () -> T).startCoroutineCancellable(completion: Continuation<T>): Unit = runSafely(completion) {
    //構(gòu)建ContinuationImpl
    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)
        //走這里
        create(probeCompletion)
    else
        createCoroutineFromSuspendFunction(probeCompletion) {
            (this as Function1<Continuation<T>, Any?>).invoke(it)
        }
}

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!!
    @Transient
    private var intercepted: Continuation<Any?>? = null
    public fun intercepted(): Continuation<Any?> =
        intercepted
            ?: (context[ContinuationInterceptor]?.interceptContinuation(this) ?: this)
                .also { intercepted = it }
}

public actual object Dispatchers {
    @JvmStatic
    public actual val Default: CoroutineDispatcher = DefaultScheduler
}

public abstract class CoroutineDispatcher :
    AbstractCoroutineContextElement(ContinuationInterceptor), ContinuationInterceptor {
    public final override fun <T> interceptContinuation(continuation: Continuation<T>): Continuation<T> =
        DispatchedContinuation(this, continuation)
}
public fun <T> (suspend () -> T).startCoroutineCancellable(completion: Continuation<T>): Unit = runSafely(completion) {
    createCoroutineUnintercepted(completion).intercepted().resumeCancellableWith(Result.success(Unit))
}

internal class DispatchedContinuation<in T>(
    //這里傳入的dispatcher在demo中是Dispatchers.Default
    @JvmField val dispatcher: CoroutineDispatcher,
    @JvmField val continuation: Continuation<T>
) : DispatchedTask<T>(MODE_UNINITIALIZED), CoroutineStackFrame, Continuation<T> by continuation {
    inline fun resumeCancellableWith(
        result: Result<T>,
        noinline onCancellation: ((cause: Throwable) -> Unit)?
    ) {
        val state = result.toState(onCancellation)
        //代碼1
        if (dispatcher.isDispatchNeeded(context)) {
            _state = state
            resumeMode = MODE_CANCELLABLE
            //代碼2
            dispatcher.dispatch(context, this)
        } else {
            //代碼3
            executeUnconfined(state, MODE_CANCELLABLE) {
                if (!resumeCancelled(state)) {
                    resumeUndispatchedWith(result)
                }
            }
        }
    }
}
internal abstract class DispatchedTask<in T>(
    @JvmField public var resumeMode: Int
) : SchedulerTask() {
    ......
}
internal actual typealias SchedulerTask = Task
internal abstract class Task(
    @JvmField var submissionTime: Long,
    @JvmField var taskContext: TaskContext
) : Runnable {
    ......
}
public abstract class CoroutineDispatcher :
    AbstractCoroutineContextElement(ContinuationInterceptor), ContinuationInterceptor {
    public abstract fun dispatch(context: CoroutineContext, block: Runnable)
    public open fun isDispatchNeeded(context: CoroutineContext): Boolean = true
}

public actual object Dispatchers {
    @JvmStatic
    public actual val Default: CoroutineDispatcher = DefaultScheduler
}
internal object DefaultScheduler : SchedulerCoroutineDispatcher(
    CORE_POOL_SIZE, MAX_POOL_SIZE,
    IDLE_WORKER_KEEP_ALIVE_NS, DEFAULT_SCHEDULER_NAME
) {
    ......
}
internal open class SchedulerCoroutineDispatcher(
    private val corePoolSize: Int = CORE_POOL_SIZE,
    private val maxPoolSize: Int = MAX_POOL_SIZE,
    private val idleWorkerKeepAliveNs: Long = IDLE_WORKER_KEEP_ALIVE_NS,
    private val schedulerName: String = "CoroutineScheduler",
) : ExecutorCoroutineDispatcher() {
    private var coroutineScheduler = createScheduler()
    private fun createScheduler() =
        CoroutineScheduler(corePoolSize, maxPoolSize, idleWorkerKeepAliveNs, schedulerName)
     override fun dispatch(context: CoroutineContext, block: Runnable): Unit = coroutineScheduler.dispatch(block)
}

internal class CoroutineScheduler(
    @JvmField val corePoolSize: Int,
    @JvmField val maxPoolSize: Int,
    @JvmField val idleWorkerKeepAliveNs: Long = IDLE_WORKER_KEEP_ALIVE_NS,
    @JvmField val schedulerName: String = DEFAULT_SCHEDULER_NAME
) : Executor, Closeable {
    override fun execute(command: Runnable) = dispatch(command)
    fun dispatch(block: Runnable, taskContext: TaskContext = NonBlockingContext, tailDispatch: Boolean = false) {
        trackTask() // this is needed for virtual time support
        //代碼1：構(gòu)建Task，Task實(shí)現(xiàn)了Runnable接口
        val task = createTask(block, taskContext)
        //代碼2：取當(dāng)前線程轉(zhuǎn)為Worker對(duì)象,Worker是一個(gè)繼承自Thread的類
        val currentWorker = currentWorker()
        //代碼3：嘗試將Task提交到本地隊(duì)列并根據(jù)結(jié)果執(zhí)行相應(yīng)的操作
        val notAdded = currentWorker.submitToLocalQueue(task, tailDispatch)
        if (notAdded != null) {
            //代碼4：notAdded不為null，則再將notAdded（Task）添加到全局隊(duì)列中
            if (!addToGlobalQueue(notAdded)) {
                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
            //代碼5: 創(chuàng)建Worker并開(kāi)始執(zhí)行該線程
            signalCpuWork()
        } else {
            // Increment blocking tasks anyway
            signalBlockingWork(skipUnpark = skipUnpark)
        }
    }
    private fun currentWorker(): Worker? = (Thread.currentThread() as? Worker)?.takeIf { it.scheduler == this }
    internal inner class Worker private constructor() : Thread() {
        .....
    }
}

internal inner class Worker private constructor() : Thread() {
    override fun run() = runWorker()
    private fun runWorker() {
        var rescanned = false
        while (!isTerminated && state != WorkerState.TERMINATED) {
            //代碼1
            val task = findTask(mayHaveLocalTasks)
            if (task != null) {
                rescanned = false
                minDelayUntilStealableTaskNs = 0L
                //代碼2
                executeTask(task)
                continue
            } else {
                mayHaveLocalTasks = false
            }
            if (minDelayUntilStealableTaskNs != 0L) {
                if (!rescanned) {
                    rescanned = true
                } else {
                    rescanned = false
                    tryReleaseCpu(WorkerState.PARKING)
                    interrupted()
                    LockSupport.parkNanos(minDelayUntilStealableTaskNs)
                    minDelayUntilStealableTaskNs = 0L
                }
                continue
            }
            tryPark()
        }
        tryReleaseCpu(WorkerState.TERMINATED)
    }
    fun findTask(scanLocalQueue: Boolean): Task? {
        if (tryAcquireCpuPermit()) return findAnyTask(scanLocalQueue)
        // If we can't acquire a CPU permit -- attempt to find blocking task
        val task = if (scanLocalQueue) {
            localQueue.poll() ?: globalBlockingQueue.removeFirstOrNull()
        } else {
            globalBlockingQueue.removeFirstOrNull()
        }
        return task ?: trySteal(blockingOnly = true)
    }
    private fun executeTask(task: Task) {
        val taskMode = task.mode
        idleReset(taskMode)
        beforeTask(taskMode)
        runSafely(task)
        afterTask(taskMode)
    }
    fun runSafely(task: Task) {
        try {
            task.run()
        } catch (e: Throwable) {
            val thread = Thread.currentThread()
            thread.uncaughtExceptionHandler.uncaughtException(thread, e)
        } finally {
            unTrackTask()
        }
    }
}

internal class DispatchedContinuation<in T>(
    @JvmField val dispatcher: CoroutineDispatcher,
    @JvmField val continuation: Continuation<T>
) : DispatchedTask<T>(MODE_UNINITIALIZED), CoroutineStackFrame, Continuation<T> by continuation {
    ......
}
internal abstract class DispatchedTask<in T>(
    @JvmField public var resumeMode: Int
) : SchedulerTask() {
    public final override fun run() {
        assert { resumeMode != MODE_UNINITIALIZED } // should have been set before dispatching
        val taskContext = this.taskContext
        var fatalException: Throwable? = null
        try {
            val delegate = delegate as DispatchedContinuation<T>
            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
                //非空，且未處于active狀態(tài)
                if (job != null && !job.isActive) {
                    //開(kāi)始之前，協(xié)程已經(jīng)被取消，將具體的Exception傳出去
                    val cause = job.getCancellationException()
                    cancelCompletedResult(state, cause)
                    continuation.resumeWithStackTrace(cause)
                } else {
                    //有異常，傳遞異常
                    if (exception != null) {
                        continuation.resumeWithException(exception)
                    } else {
                        //代碼1
                        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())
        }
    }
}