8000 Interleave: Do not call GetEnumerator eagerly by Orace · Pull Request #730 · morelinq/MoreLINQ · GitHub
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Interleave: Do not call GetEnumerator eagerly #730

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Merged
merged 3 commits into from
Aug 11, 2020
Merged

Interleave: Do not call GetEnumerator eagerly #730

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2142e40
Renamed TestInterleaveDisposesOnError to TestInterleaveDisposesOnErro…
Orace Dec 12, 2019
673b42c
Avoid eagerly calls to GetEnumerator in Interleave
Orace Dec 12, 2019
0316143
Add TestInterleaveDoNotCallGetEnumeratorEagerly
Orace Dec 12, 2019
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48 changes: 37 additions & 11 deletions MoreLinq.Test/InterleaveTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -36,29 +36,55 @@ public void TestInterleaveIsLazy()
}

/// <summary>
/// Verify that interleaving do not call enumerators MoveNext method eagerly
/// Verify that interleaving disposes those enumerators that it managed
/// to open successfully
/// </summary>
[Test]
public void TestInterleaveDoNoCallMoveNextEagerly()
public void TestInterleaveDisposesOnErrorAtGetEnumerator()
{
var sequenceA = Enumerable.Range(1, 1);
var sequenceB = MoreEnumerable.From<int>(() => throw new TestException());
using var sequenceA = TestingSequence.Of<int>();
var sequenceB = new BreakingSequence<int>();

sequenceA.Interleave(sequenceB).Take(1).Consume();
// Expected and thrown by BreakingSequence
Assert.Throws<InvalidOperationException>(() => sequenceA.Interleave(sequenceB).Consume());
}

/// <summary>
/// Verify that interleaving disposes those enumerators that it managed
/// to open successfully
/// </summary>
[Test]
public void TestInterleaveDisposesOnError()
public void TestInterleaveDisposesOnErrorAtMoveNext()
{
using (var sequenceA = TestingSequence.Of<int>())
{
Assert.Throws<InvalidOperationException>(() => // Expected and thrown by BreakingSequence
sequenceA.Interleave(new BreakingSequence<int>()).Consume());
}
using var sequenceA = TestingSequence.Of<int>();
using var sequenceB = MoreEnumerable.From<int>(() => throw new TestException()).AsTestingSequence();

// Expected and thrown by sequenceB
Assert.Throws<TestException>(() => sequenceA.Interleave(sequenceB).Consume());
}

/// <summary>
/// Verify that interleaving do not call enumerable GetEnumerator method eagerly
/// </summary>
[Test]
public void TestInterleaveDoNotCallGetEnumeratorEagerly()
{
var sequenceA = TestingSequence.Of(1);
var sequenceB = new BreakingSequence<int>();

sequenceA.Interleave(sequenceB).Take(1).Consume();
}

/// <summary>
/// Verify that interleaving do not call enumerators MoveNext method eagerly
/// </summary>
[Test]
public void TestInterleaveDoNoCallMoveNextEagerly()
{
var sequenceA = Enumerable.Range(1, 1);
var sequenceB = MoreEnumerable.From<int>(() => throw new TestException());

sequenceA.Interleave(sequenceB).Take(1).Consume();
}

/// <summary>
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20 changes: 16 additions & 4 deletions MoreLinq/Interleave.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -53,17 +53,29 @@ public static IEnumerable<T> Interleave<T>(this IEnumerable<T> sequence, params
return _(); IEnumerable<T> _()
{
var sequences = new[] { sequence }.Concat(otherSequences);

// produce an enumerators collection for all IEnumerable<T> instances passed to us
var enumerators = sequences.Select(e => e.GetEnumerator()).Acquire();
var enumerators = new List<IEnumerator<T>>();

try
{
foreach (var enumerator in sequences.Select(s => s.GetEnumerator()))
{
enumerators.Add(enumerator);
if (enumerator.MoveNext())
{
yield return enumerator.Current;
}
else
{
enumerators.Remove(enumerator);
enumerator.Dispose();
}
}

var hasNext = true;
while (hasNext)
{
hasNext = false;
for (var i = 0; i < enumerators.Length; i++)
for (var i = 0; i < enumerators.Count; i++)
{
var enumerator = enumerators[i];
if (enumerator == null)
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0