问题
有几个任务是并行运行的,all,none或者其中任何一个都可能抛出异常.当所有任务完成后,必须报告所有可能发生的异常(通过日志,电子邮件,控制台输出……等等).
预期的行为
我可以使用asq lambdas通过linq构建所有任务,然后等待它们与Task.WhenAll(任务)并行运行.然后我可以捕获AggregateException并报告每个单独的内部异常.
实际行为
抛出了AggregateException,但它只包含一个内部异常,无论抛出多少个别异常.
最小的完整可验证的例子
static void Main(string[] args)
{
try
{
ThrowSeveralExceptionsAsync(5).Wait();
}
catch (AggregateException ex)
{
ex.Handle(innerEx =>
{
Console.WriteLine($"\"{innerEx.Message}\" was thrown");
return true;
});
}
Console.ReadLine();
}
private static async Task ThrowSeveralExceptionsAsync(int nExceptions)
{
var tasks = Enumerable.Range(0,nExceptions)
.Select(async n =>
{
await ThrowAsync(new Exception($"Exception #{n}"));
});
await Task.WhenAll(tasks);
}
private static async Task ThrowAsync(Exception ex)
{
await Task.Run(() => {
Console.WriteLine($"I am going to throw \"{ex.Message}\"");
throw ex;
});
}
产量
请注意,由于竞争条件,“我要投掷”消息的输出顺序可能会发生变化.
I am going to throw "Exception #0" I am going to throw "Exception #1" I am going to throw "Exception #2" I am going to throw "Exception #3" I am going to throw "Exception #4" "Exception #0" was thrown
解决方法
那是因为等待“解包”聚合异常并且总是抛出第一个异常(如
await的文档中所述),即使等待Task.WhenAll显然会导致多个错误.您可以访问聚合异常,例如：
var whenAll = Task.WhenAll(tasks);
try {
await whenAll;
}
catch {
// this is `AggregateException`
throw whenAll.Exception;
}
或者你可以循环遍历任务并检查每个任务的状态和异常.
请注意,在修复之后,您还需要做一件事：
try {
ThrowSeveralExceptionsAsync(5).Wait();
}
catch (AggregateException ex) {
// flatten,unwrapping all inner aggregate exceptions
ex.Flatten().Handle(innerEx => {
Console.WriteLine($"\"{innerEx.Message}\" was thrown");
return true;
});
}
因为ThrowSeveralExceptionsAsync返回的任务包含我们抛出的AggregateException,包含在另一个AggregateException中.
