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kotlin - 在 runBlocking 中使用 coroutineScope 有什么效果？

问题描述

在 kotlin coroutines doc中，它解释了“runBlocking 和 coroutineScope 之间的区别”：

范围构建器

除了不同构建器提供的协程作用域外，还可以使用 coroutineScope 构建器来声明自己的作用域。它创建了一个协程范围，并且在所有启动的子进程完成之前不会完成。The main difference between runBlocking and coroutineScope is that the latter does not block the current thread while waiting for all children to complete.

我不太明白，示例代码显示

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
}

日志：

2019-05-16 10:47:45.107 12239-12239 +++ before enter runBlocking{}
2019-05-16 10:47:45.219 12239-12239 +++ Task from coroutine scope
2019-05-16 10:47:45.320 12239-12239 +++ Task from runBlocking
2019-05-16 10:47:45.620 12239-12239 +++ Task from nested launch
2019-05-16 10:47:45.621 12239-12239 +++ ---after exit runBlocking{}

并且按预期+++ Task from nested launch显示+++ Task from runBlocking，因为它有 500L 延迟。

但是如果在块之后添加一些其他launch的构建器coroutineScop{}，结果会令人困惑。

这里有两个launch是在coroutineScop{}30L 和 100L 延迟之后添加的。

我期待看到延迟的日志30L应该在 延迟300L 之前coroutineScop{}出现launchcoroutineScop{}

fun testCoroutines() {
Log.e("+++", "+++ enter testCoroutines_3")
runBlocking {
    launch {
        println("+++ start Task from runBlocking, with 200L delay")
        delay(200L)
        println("+++ end Task from runBlocking, with 200L delay")
    }

    launch {
        println("+++ start Task from runBlocking, with 50L delay")
        delay(50L)
        println("+++ end Task from runBlocking, with 50L delay")
    }

    launch {
        println("+++ start Task from runBlocking, with 70L delay")
        delay(70L)
        println("+++ end Task from runBlocking, with 70L delay")
    }

    coroutineScope {
        println("+++ enter Task from coroutineScope")
        // Creates a coroutine scope
        launch {
            Log.v("+++", "+++ === start Task from nested launch, 500L")
            delay(500L)
            Log.v("+++", "+++ --- end Task from nested launch, 500L")
        }

        delay(100L)
        println("+++ in Task from coroutineScope after delay(100L)")

        launch {
            Log.v("+++", "+++ === start Task from nested launch, 300L")
            delay(300L)
            Log.v("+++", "+++ --- end Task from nested launch, 300L")
        }

        println("+++ --- exit Task from coroutine scope") // This line will be printed before the nested launch
    }

    launch {
        println("+++ start Task from runBlocking, with 30L delay")
        delay(30L)
        println("+++ end Task from runBlocking, with 30L delay")
    }

    launch {
        println("+++ start Task from runBlocking, with 100L delay")
        delay(100L)
        println("+++ end Task from runBlocking, with 100L delay")
    }

}

Log.e("+++", "--- exit  testCoroutines_3 scope is over") // This line is not printed until the nested launch completes

}

日志：

10:35:05.819 4657-4657 +++ enter testCoroutines_3
10:35:05.828 4657-4657 +++ enter Task from coroutineScope
10:35:05.833 4657-4657 +++ start Task from runBlocking, with 200L delay
10:35:05.833 4657-4657 +++ start Task from runBlocking, with 50L delay
10:35:05.833 4657-4657 +++ start Task from runBlocking, with 70L delay
10:35:05.834 4657-4657 +++ === start Task from nested launch, 500L
10:35:05.885 4657-4657 +++ end Task from runBlocking, with 50L delay
10:35:05.905 4657-4657 +++ end Task from runBlocking, with 70L delay
10:35:05.932 4657-4657 +++ in Task from coroutineScope after delay(100L)
10:35:05.933 4657-4657 +++ --- exit Task from coroutine scope
10:35:05.935 4657-4657 +++ === start Task from nested launch, 300L
10:35:06.034 4657-4657 +++ end Task from runBlocking, with 200L delay
10:35:06.235 4657-4657 +++ --- end Task from nested launch, 300L
10:35:06.334 4657-4657 +++ --- end Task from nested launch, 500L
10:35:06.335 4657-4657 +++ start Task from runBlocking, with 30L delay
10:35:06.335 4657-4657 +++ start Task from runBlocking, with 100L delay
10:35:06.366 4657-4657 +++ end Task from runBlocking, with 30L delay
10:35:06.436 4657-4657 +++ end Task from runBlocking, with 100L delay
10:35:06.437 4657-4657--- exit  testCoroutines_3 scope is over

认为至少+++ start Task from runBlocking, with 30L delay 应该在之后+++ === start Task from nested launch, 500L和之前出现+++ end Task from runBlocking, with 50L delay，但它并没有出现，毕竟launch完成后+++ --- end Task from nested launch, 500L。

协同程序块中的coroutineScope做什么？

（我正在使用 android 应用程序进行测试，单击按钮调用testCoroutines）

标签： kotlinkotlin-coroutinescoroutinescope

解决方案

coroutineScope非阻塞的事实并不意味着它不等待其子协程完成。

事实上，两者runBlocking都会coroutineScope等待每个子协程完成后再完成。

两者之间的真正区别在于他们如何等待。runBlocking阻塞当前线程，同时coroutineScope挂起当前协程。

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