如果返回任务的方法抛出异常？ [英] Should methods that return Task throw exceptions?
问题描述
返回工作有两种选择报告的错误方法：
Methods that return Task have two options for reporting an error:
- 在抛出异常的时候了
- 在返回将与除了完成任务
如果主叫方希望这两种类型的错误报告，或者是有一些标准/协议限制任务行为的第二个选项？
Should the caller expect both types of error reporting or is there some standard/agreement that limits task behavior to the second option?
例如：
class PageChecker {
Task CheckWebPage(string url) {
if(url == null) // argument check
throw Exception("Bad url");
if(!HostPinger.IsHostOnline(url)) // some other synchronous check
throw Exception("Host is down");
return Task.Factory.StartNew(()=> {
// asynchronous check
if(PageDownloader.GetPageContent(url).Contains("error"))
throw Exception("Error on the page");
});
}
}
处理两种类型看起来pretty的丑陋：
Handling both types looks pretty ugly:
try {
var task = pageChecker.CheckWebPage(url);
task.ContinueWith(t =>
{
if(t.Exception!=null)
ReportBadPage(url);
});
}
catch(Exception ex) {
ReportBadPage(url);
}
使用异步/等待可能会有帮助，但有对于普通的.NET 4的解决方案，而不异步支持？
Using async/await may help, but is there a solution for plain .net 4 without async support?
推荐答案
大多数工作 -returning方法适用于具有使用异步 / 等待（，因此不应该使用 Task.Run 或任务.Factory.StartNew 内部）。
Most Task-returning methods are intended for use with async/await (and as such should not use Task.Run or Task.Factory.StartNew internally).
请注意，与调用异步方法的常用的方式，它并不重要的例外是如何引发
Note that with the common way of calling asynchronous methods, it doesn't matter how the exception is thrown:
await CheckWebPageAsync();
所不同的只是来当该方法被调用，然后等待后面：
The difference only comes in when the method is called and then awaited later:
List<Task> tasks = ...;
tasks.Add(CheckWebPagesAsync());
...
await Task.WhenAll(tasks);
不过，通常是呼叫（ CheckWebPagesAsync（））和等待在$ C的同一个块$ C，所以他们会在同一个尝试 / 抓反正块，而在这种情况下，它也（通常）没有关系。
However, usually the call (CheckWebPagesAsync()) and the await are in the same block of code, so they would be in the same try/catch block anyway, and in that case it also (usually) doesn't matter.
有没有一些标准/协议限制任务行为的第二个选项？
is there some standard/agreement that limits task behavior to the second option?
没有标准。 preconditions是一类愚蠢的例外的，所以它其实并不重要，它是如何抛出，因为它的不应该被抓反正。
There is no standard. Preconditions are a type of boneheaded exception, so it doesn't really matter how it's thrown because it should never be caught anyway.
乔恩斯基特是preconditions应直接抛出的观点（外返回的任务）：
Jon Skeet is of the opinion that preconditions should be thrown directly ("outside" the returned task):
Task CheckWebPageAsync(string url) {
if(url == null) // argument check
throw Exception("Bad url");
return CheckWebPageInternalAsync(url);
}
private async Task CheckWebPageInternalAsync(string url) {
if((await PageDownloader.GetPageContentAsync(url)).Contains("error"))
throw Exception("Error on the page");
}
这提供了一个很好的平行LINQ运营商，这些都保证了异常的早像这样（枚举外）。
This provides a nice parallel to LINQ operators, which are guaranteed to throw exceptions "early" like this (outside the enumerator).
但我不认为这是必要的。我发现任务中抛preconditions当code是简单的：
But I don't think that's necessary. I find the code is simpler when throwing preconditions within the task:
async Task CheckWebPageAsync(string url) {
if(url == null) // argument check
throw Exception("Bad url");
if((await PageDownloader.GetPageContentAsync(url)).Contains("error"))
throw Exception("Error on the page");
}
记住，应永远不会有任何code映入preconditions ，所以在现实世界中，应该没有任何区别的异常是如何抛出。
Remember, there should never be any code that catches preconditions, so in the real world, it shouldn't make any difference how the exception is thrown.
在另一方面，这种的是的一个点上，我居然跟乔恩斯基特不同意。所以，你的里程可能会有所不同...很多。 ：）
On the other hand, this is one point where I actually disagree with Jon Skeet. So your mileage may vary... a lot. :)
这篇关于如果返回任务的方法抛出异常？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
