8000 `Merge` masks original exception with an `ArgumentException` about no tasks · Issue #1056 · morelinq/MoreLINQ · GitHub
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Merge masks original exception with an ArgumentException about no tasks #1056

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atifaziz opened this issue Jan 19, 2024 · 0 comments · Fixed by #1059
Closed

Merge masks original exception with an ArgumentException about no tasks #1056

atifaziz opened this issue Jan 19, 2024 · 0 comments · Fixed by #1059
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@atifaziz
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bug
Milestone
4.2.0

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@atifaziz
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Code to reproduce:

var items =
    Enumerable.Range(1, 3)
              .Select(n => Source(n, n % 2 is 0))
              .Merge();

await foreach (var item in items)
    Console.WriteLine(item);

async IAsyncEnumerable<int> Source(int n, bool fail = false)
{
    await Task.Delay(TimeSpan.FromSeconds(n));
    yield return n;
    if (fail)
        throw new();
}

When run, it will output:

1
2
System.ArgumentException: The tasks argument contains no tasks. (Parameter 'tasks')
   at System.Threading.Tasks.Task.WhenAny[TTask](ReadOnlySpan`1 tasks)
   at System.Threading.Tasks.Task.WhenAny[TTask](IEnumerable`1 tasks)
   at System.Threading.Tasks.Task.WhenAny[TResult](IEnumerable`1 tasks)
   at MoreLinq.Experimental.Async.ExperimentalEnumerable.<>c__DisplayClass1_0`1.<<Merge>g__Async|0>d.MoveNext()
--- End of stack trace from previous location ---
   at MoreLinq.Experimental.Async.ExperimentalEnumerable.<>c__DisplayClass1_0`1.<<Merge>g__Async|0>d.System.Threading.Tasks.Sources.IValueTaskSource<System.Boolean>.GetResult(Int16 token)
   at UserQuery.Main() in C:\Users\johndoe\AppData\Local\Temp\LINQPad8\_hiuxehhq\uljkai\LINQPadQuery:line 7
   at UserQuery.Main() in C:\Users\johndoe\AppData\Local\Temp\LINQPad8\_hiuxehhq\uljkai\LINQPadQuery:line 7

It throws ArgumentException when it should have thrown Exception.

The problem seems to be due to the following clean-up loop, which can call Task.WhenAny with zero tasks:

MoreLINQ/MoreLinq/Experimental/Async/Merge.cs

Lines 204 to 211 in 0e154ef

if (pendingTaskList is { Count: > 0 })
{
while (await Task.WhenAny(pendingTaskList)
.ConfigureAwait(false) is { } completedTask)
{
_ = pendingTaskList.Remove(completedTask);
}
}

@atifaziz atifaziz added the bug label Jan 19, 2024
@atifaziz atifaziz added this to the vNext milestone Jan 19, 2024
@atifaziz atifaziz self-assigned this Jan 19, 2024
@atifaziz atifaziz mentioned this issue Jan 20, 2024
Merged
@atifaziz atifaziz modified the milestones: vNext, 4.2.0 Jan 20, 2024
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Fix pending tasks wait loop in async streams Merge atifaziz/MoreLINQ
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