为什么coroutineScope会阻止该进程？

Question

在this official documentation中，它说coroutineScope只是挂起，释放底层线程以用于其他用途。

但在示例代码中，它看起来会阻塞下一个进程，因为在coroutineScope中完成代码块之前不会执行println("Coroutine scope is over")。

import kotlinx.coroutines.*

fun main() = runBlocking { // this: CoroutineScope
    launch { 
        delay(200L)
        println("Task from runBlocking")
    }
    
    coroutineScope { // Creates a coroutine scope
        launch {
            delay(500L) 
            println("Task from nested launch")
        }
    
        delay(100L)
        println("Task from coroutine scope") // This line will be printed before the nested launch
    }
    
    println("Coroutine scope is over") // This line is not printed until the nested launch completes
}

我知道runBlocking要等到它所有的子进程都完成。因此，在我看来，runBlocking应该在执行完println("Coroutine scope is over")行之后等待coroutineScope完成。

为什么在本例中coroutineScope会阻塞线程？

Answer 1

coroutineScope挂起了CoroutineScope作用域，因此“println(”协程作用域已结束“)”行将在前一个coroutineScope完成后执行。您可以看到coroutineScope函数的代码：

public suspend fun <R> coroutineScope(block: suspend CoroutineScope.() -> R): R {
contract {
    callsInPlace(block, InvocationKind.EXACTLY_ONCE)
}
return suspendCoroutineUninterceptedOrReturn { uCont ->
    val coroutine = ScopeCoroutine(uCont.context, uCont)
    coroutine.startUndispatchedOrReturn(coroutine, block)
}}