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[release/6.0-rc2] Fix corner-case handling of cancellation exception in ForEachAsync #59237

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Merged
stephentoub merged 2 commits into from
Sep 17, 2021
Merged

[release/6.0-rc2] Fix corner-case handling of cancellation exception in ForEachAsync #59237

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f056f42
Fix corner-case handling of cancellation exception in ForEachAsync
stephentoub Sep 13, 2021
d92201e
Stop filtering out cancellation exceptions in Parallel.ForEachAsync
stephentoub Sep 16, 2021
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16 changes: 4 additions & 12 deletions ...aries/System.Threading.Tasks.Parallel/src/System/Threading/Tasks/Parallel.ForEachAsync.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -480,18 +480,10 @@ public void Complete()
}
else
{
// Fault with all of the received exceptions, but filter out those due to inner cancellation,
// as they're effectively an implementation detail and stem from the original exception.
Debug.Assert(_exceptions.Count > 0, "If _exceptions was created, it should have also been populated.");
for (int i = 0; i < _exceptions.Count; i++)
{
if (_exceptions[i] is OperationCanceledException oce && oce.CancellationToken == Cancellation.Token)
{
_exceptions[i] = null!;
}
}
_exceptions.RemoveAll(e => e is null);
Debug.Assert(_exceptions.Count > 0, "Since external cancellation wasn't requested, there should have been a non-cancellation exception that triggered internal cancellation.");
// Fail the task with the resulting exceptions. The first should be the initial
// exception that triggered the operation to shut down. The others, if any, may
// include cancellation exceptions from other concurrent operations being canceled
// in response to the primary exception.
taskSet = TrySetException(_exceptions);
}

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62 changes: 58 additions & 4 deletions src/libraries/System.Threading.Tasks.Parallel/tests/ParallelForEachAsyncTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -618,6 +618,64 @@ static async IAsyncEnumerable<int> Iterate()
Assert.True(t.IsCanceled);
}

[ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
[InlineData(false)]
[InlineData(true)]
public async Task Cancellation_FaultsForOceForNonCancellation(bool internalToken)
{
static async IAsyncEnumerable<int> Iterate()
{
int counter = 0;
while (true)
{
await Task.Yield();
yield return counter++;
}
}

var cts = new CancellationTokenSource();

Task t = Parallel.ForEachAsync(Iterate(), new ParallelOptions { CancellationToken = cts.Token }, (item, cancellationToken) =>
{
throw new OperationCanceledException(internalToken ? cancellationToken : cts.Token);
});

await Assert.ThrowsAnyAsync<OperationCanceledException>(() => t);
Assert.True(t.IsFaulted);
}

[ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
[InlineData(0, 4)]
[InlineData(1, 4)]
[InlineData(2, 4)]
[InlineData(3, 4)]
[InlineData(4, 4)]
public async Task Cancellation_InternalCancellationExceptionsArentFilteredOut(int numThrowingNonCanceledOce, int total)
{
var cts = new CancellationTokenSource();

var barrier = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
int remainingCount = total;

Task t = Parallel.ForEachAsync(Enumerable.Range(0, total), new ParallelOptions { CancellationToken = cts.Token, MaxDegreeOfParallelism = total }, async (item, cancellationToken) =>
{
// Wait for all operations to be started
if (Interlocked.Decrement(ref remainingCount) == 0)
{
barrier.SetResult();
}
await barrier.Task;

throw item < numThrowingNonCanceledOce ?
new OperationCanceledException(cancellationToken) :
throw new FormatException();
});

await Assert.ThrowsAnyAsync<Exception>(() => t);
Assert.Equal(total, t.Exception.InnerExceptions.Count);
Assert.Equal(numThrowingNonCanceledOce, t.Exception.InnerExceptions.Count(e => e is OperationCanceledException));
}

[ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
public void Exception_FromGetEnumerator_Sync()
{
Expand Down Expand Up @@ -672,7 +730,6 @@ static IEnumerable<int> Iterate()
Task t = Parallel.ForEachAsync(Iterate(), (item, cancellationToken) => default);
await Assert.ThrowsAsync<FormatException>(() => t);
Assert.True(t.IsFaulted);
Assert.Equal(1, t.Exception.InnerExceptions.Count);
}

[ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
Expand All @@ -694,7 +751,6 @@ static async IAsyncEnumerable<int> Iterate()
Task t = Parallel.ForEachAsync(Iterate(), (item, cancellationToken) => default);
await Assert.ThrowsAsync<FormatException>(() => t);
Assert.True(t.IsFaulted);
Assert.Equal(1, t.Exception.InnerExceptions.Count);
}

[ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
Expand Down Expand Up @@ -771,7 +827,6 @@ public async Task Exception_FromDispose_Sync()
Task t = Parallel.ForEachAsync((IEnumerable<int>)new ThrowsExceptionFromDispose(), (item, cancellationToken) => default);
await Assert.ThrowsAsync<FormatException>(() => t);
Assert.True(t.IsFaulted);
Assert.Equal(1, t.Exception.InnerExceptions.Count);
}

[ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
Expand All @@ -780,7 +835,6 @@ public async Task Exception_FromDispose_Async()
Task t = Parallel.ForEachAsync((IAsyncEnumerable<int>)new ThrowsExceptionFromDispose(), (item, cancellationToken) => default);
await Assert.ThrowsAsync<DivideByZeroException>(() => t);
Assert.True(t.IsFaulted);
Assert.Equal(1, t.Exception.InnerExceptions.Count);
}

[ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
Expand Down