Coroutines and exceptions: things to know

栏目: IT技术 · 发布时间: 4年前

内容简介:Coroutines are an awesome way to write async code. Your code looks almost similar to the sync equivalent but it's not blocking.When everything goes according to plan, no need to worry about weird behavior from coroutines. What happens though when things do

Coroutines are an awesome way to write async code. Your code looks almost similar to the sync equivalent but it's not blocking.

When everything goes according to plan, no need to worry about weird behavior from coroutines. What happens though when things don't go according to plan, i.e. exceptions are thrown? Can those exceptions be caught like regular sync code?

The answer depends on the coroutine builder used.

async

The async coroutine builder works as you would expect, i.e. similar to how sync code handles exceptions. They rely on the user to handle the exception, otherwise, it's thrown as unhandled.

val deferred = GlobalScope.async {
    throw ArithmeticException()
}
    
try {
    deferred.await()
} catch (e: ArithmeticException) {
    // Exception caught
}

launch

On the other hand, launch coroutine builder treats exceptions as unhandled. These can be caught by  Java's Thread.uncaughtExceptionHandler .

try {
    GlobalScope.launch {
        throw ArithmeticException()
    }
} catch (e: ArithmeticException) {
    // Exception will *not* be caught
}

Of course, relying on Thread.uncaughtExceptionHandler is not a great idea to handle all exceptions across your app.

Coroutine builders accept an additional CoroutineExceptionHandler parameter for these cases.

val handler = CoroutineExceptionHandler { _, exception -> 
    // Exception caught
}

GlobalScope.launch(handler) {
    throw ArithmeticException()
}

Child-parent exception relationship

Speaking of exceptions, we should note the default behavior of coroutines when they encounter an exception.

A child coroutine encountering an exception will cancel itself and its parent coroutine with that exception.  

val handler = CoroutineExceptionHandler { _, exception -> 
    // ArithmeticException will be caught.
    //
    // 1st child will not complete because parent is cancelled (i.e. and
    // children as well)
}

GlobalScope.launch(handler) {
    launch { // 1st child
        delay(Long.MAX_VALUE)
        print("This will not be printed")
    }
    launch { // 2nd child
        throw ArithmeticException()
    }
}

A small detail, but the original exception will be handled by the parent after all its children coroutines terminate. So, if the 2nd child was running with NonCancellable context, the handler would be called after the completion of the 2nd child.

val handler = CoroutineExceptionHandler { _, exception -> 
    // 1st child complete, then ArithmeticException will be caught.
}

GlobalScope.launch(handler) {
    launch(NonCancellable) { // 1st child
        delay(Long.MAX_VALUE)
        print("This will be printed")
    }
    launch { // 2nd child
        throw ArithmeticException()
    }
}

A special exception

The CancellationException is treated differently than the rest of the exceptions. It's ignored by the exception handlers and does not cause the cancellation of the parent coroutine.

launch {
    val child = launch {
        delay(Long.MAX_VALUE)
    }
    child.join()
    child.cancel() // Parent is not cancelled, 
                   // although child is throwing a CancellationExeption
    print("Hello from parent")
}

Multiple exceptions

In case multiple children throw exceptions, the first one wins. There is a way to catch additional exceptions that might have been thrown after the first one.

val handler = CoroutineExceptionHandler { _, exception -> 
    // ArithmeticException will be caught (from 2nd child).
    //
    // IOException can be accessed using exception.suppressed (from 1st child) 
}

GlobalScope.launch(handler) {
    launch { // 1st child
        try {
            delay(Long.MAX_VALUE)
        }
        finally {
            throw IOException()
        }
    }
    launch { // 2nd child
        throw ArithmeticException()
    }
}

Hopefully, the relationship between coroutines and exception is a bit clearer now. You can always refer to the excellent Kotlin docs . Happy throwing!


以上所述就是小编给大家介绍的《Coroutines and exceptions: things to know》,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对 码农网 的支持!

查看所有标签

猜你喜欢:

本站部分资源来源于网络,本站转载出于传递更多信息之目的,版权归原作者或者来源机构所有,如转载稿涉及版权问题,请联系我们

一个APP的诞生

一个APP的诞生

Carol 炒炒、刘焯琛 / 电子工业出版社 / 2016-7-1 / 79

在移动互联网高度发达的今天,一个个APP,成为我们通向网络世界的窗口。它的诞生流程,令不少对互联网世界产生幻想甚至试图投身其中的年轻人充满了好奇。 《一个APP 的诞生》就是这样一步一步拆分一个APP 的诞生过程。从前期市场调研,竞品分析开始,一直到设计规范,界面图标,设计基础,流程管理,开发实现,市场推广,服务设计,甚至跨界融合,都有陈述。 《一个APP 的诞生》被定义是一本教科书,......一起来看看 《一个APP的诞生》 这本书的介绍吧!

JS 压缩/解压工具
JS 压缩/解压工具

在线压缩/解压 JS 代码

MD5 加密
MD5 加密

MD5 加密工具

HEX HSV 转换工具
HEX HSV 转换工具

HEX HSV 互换工具