为什么CoroutineExceptionHandler只有在coroutineContext为MainScope()时才能启动？

Question

我有下面的代码并故意触发异常被 errorHandler

捕获

    private var coroutineScope: CoroutineScope? = null
    private val mainThreadSurrogate = newSingleThreadContext("Test Main")

    @Before
    fun setUp() {
        Dispatchers.setMain(mainThreadSurrogate)
    }

    @After
    fun tearDown() {
        // reset main dispatcher to the original Main dispatcher       
        Dispatchers.resetMain()
        mainThreadSurrogate.close()
    }

    private val errorHandler = CoroutineExceptionHandler { context, error ->
        println("Launch Exception ${Thread.currentThread()}")
        coroutineScope?.launch(Dispatchers.Main) {
            println("Launch Exception Result ${Thread.currentThread()}")
        }
    }

    @Test
    fun testData() {
        runBlocking {
            coroutineScope = MainScope()
            coroutineScope?.launch(errorHandler) {
                println("Launch Fetch Started ${Thread.currentThread()}")
                throw IllegalStateException("error")
            }?.join()
        }
    }

这将导致

Launch Fetch Started Thread[Test Main @coroutine#2,5,main]
Launch Exception Thread[Test Main @coroutine#2,5,main]
Launch Exception Result Thread[Test Main @coroutine#3,5,main]

如果我将 coroutineScope = MainScope() 更改为

coroutineScope = CoroutineScope(Dispatchers.Main)
coroutineScope = CoroutineScope(Dispatchers.IO)

coroutineScope?.launch(Dispatchers.Main) {...} 不会运行即 Launch Exception Result ... 不会打印。

为什么会这样？

Answer 1

显然，我们需要使用 SupervisorJob() 创建一个 Scope，这样父作业就不会受到子作业崩溃的影响。

coroutineScope = CoroutineScope(SupervisorJob() + Dispatchers.IO)

请注意 MainScope() 是 CoroutineScope(SupervisorJob() + Dispatchers.Main)。

如SupervisorJob

所述

A failure or cancellation of a child does not cause the supervisor job to fail and does not affect its other children, so a supervisor can implement a custom policy for handling failures of its children

为什么CoroutineExceptionHandler只有在coroutineContext为MainScope()时才能启动？

Why CoroutineExceptionHandler can only perform launch when the coroutineContext is MainScope()?

kotlin

kotlin-coroutines