Task.WaitAll，如何找到导致 AggregateException 的任务

Question

Let's say that I got the following code:

var tasks = BuildTaskList();
try
{
    Task.WaitAll(tasks.ToArray());
}
catch (AggregateException exception)
{

}

How do I know which task threw which of the exceptions in exception.InnerExceptions ?

Answer 1

You still have the list of Tasks , and each Task has an Exception property. Using that you can figure out which exceptions belong with which Task .

But, if you can, it'd be better to use Task.WhenAll or TaskFactory.ContinueWhenAll than do a blocking Wait.

Answer 2

var throwers = tasks.Where(task => task.Exception != null);

Answer 3

        var t1 = Task.Factory.StartNew(() => Console.WriteLine("Task 1"));
        var t2 = Task.Factory.StartNew(() => Console.WriteLine("Task 2"));
        var t3 = Task.Factory.StartNew(() => { throw new InvalidOperationException(); });
        var t4 = Task.Factory.StartNew(() => Console.WriteLine("Task 4"));

        Task.Factory.ContinueWhenAll(new[] { t1, t2, t3, t4 }, tasks =>
            {
                foreach (var t in tasks)
                {
                    if (t.Status == TaskStatus.Faulted)
                    {
                        // this will run for t3
                        Console.WriteLine("This task has been faulted.");
                    }
                }
            });

Answer 4

Option1 (credit to @theodor-zoulias comment):

You can set the Exception.Data property with the task name:

var task1 = Task.Factory.StartNew(() =>
{
    try
    {
        throw new Exception();
    }
    catch (Exception exception)
    {
        exception.Data["task"] = "task1";
        throw exception;
    }
});

var task2 = Task.Factory.StartNew(() =>
{
    try
    {
        throw new Exception();
    }
    catch (Exception exception)
    {
        exception.Data["task"] = "task2";
        throw exception;
    }
});

try
{
    Task.WaitAll(task1, task2);
}
catch (AggregateException ae)
{
    foreach (var exception in ae.InnerExceptions)
    {
        Console.WriteLine($"Exception was thrown by {exception.Data["task"]}");
    }
}

Option2:

If you don't mind loosing the name of the exception's assembly information, You can set the Exception.Source ( doc ) property of the thrown exception based on the task name and look at it while iterating:

var t1 = Task.Factory.StartNew(() => 
{
    throw new Exception() { Source = "t1" };
});
var t2 = Task.Factory.StartNew(() => 
{
    throw new Exception() { Source = "t2" };
});

try
{
    Task.WaitAll(t1, t2);
}
catch (AggregateException ae)
{
    foreach (var exception in ae.InnerExceptions)
    {
        Console.WriteLine($"Exception was thrown by {exception.Source}");
    }
}

Will output:

Exception was thrown by t1

Exception was thrown by t2