kotlin 协程的执行优先级

Question

我需要帮助理解以下 2 段代码的结果

第一个片段

fun main() = runBlocking { 
    launch {
        println("Task from runBlocking")
    }

    coroutineScope { 
        launch {
            println("Task from nested launch")
        }

        println("Task from coroutine scope")
    }

    println("Coroutine scope is over")
}

而且，第二个片段

fun main() = runBlocking { 
    launch {
        println("Task from runBlocking")
    }

    println("Coroutine scope is over") 
}

第一个片段的结果是:

Task from coroutine scope
Task from runBlocking
Task from nested launch
Coroutine scope is over

第二个片段的结果是:

Coroutine scope is over
Task from runBlocking

所以，问题是为什么这些语句按这个顺序打印？

Answer 1

对于 1st snippet您正在使用 coroutineScope正如您从 documentation 中看到的那样定义为 suspend函数，所以它阻塞了当前线程和 "Coroutine scope is over"直到 coroutineScope 才打印块已完成。

对于 2nd snippet字符串 "Coroutine scope is over"印在 "Task from run blocking" 之前因为它的 println 是在主线程中执行的，而 launch它在工作线程中运行尚未完成其工作。

fun mainOne() = runBlocking {
  launch {
      println("Task from runBlocking")
  }

  // coroutineScope is defined as a suspend function, so it's blocking the current thread
  coroutineScope {

      launch {
          // worker thread, slower than main thread, printed after "Task from coroutine scope"
          println("Task from nested launch")
      }
      // main thread, printed before "Task from nested launch" within CoroutineScope
      println("Task from coroutine scope")
  }

  // main thread is now free to run and it prints the string below
  println("Coroutine scope is over")
}


fun mainTwo() = runBlocking {
    launch {
        // worker thread, slower than main thread, printed after "Coroutine scope is over" due to concurrency
        println("Task from runBlocking")
    }
    // main thread is running and prints the string below before launch job has finished.
    // If you put a delay here you'll notice that launch job gets completed before "Coroutine scope is over"
    // E.g delay(2000)
    println("Coroutine scope is over")
}

希望这是有道理的:)