Task.WaitAll, how to find the tasks causing AggregateException

问题

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?

回答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.

回答2:

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

回答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.");
                    }
                }
            });

回答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

来源：https://stackoverflow.com/questions/18314046/task-waitall-how-to-find-the-tasks-causing-aggregateexception

标签

task-parallel-library