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Fix Memoize Implementation #898

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Fix Memoize Implementation #898

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8f6febb
Fix Memoize implementation
viceroypenguin Nov 20, 2022
a2308bf
Fix Tests per changed implementation
viceroypenguin Nov 20, 2022
82e213b
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viceroypenguin Nov 20, 2022
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6 changes: 2 additions & 4 deletions MoreLinq.Test/CartesianTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -154,10 +154,8 @@ public void TestCartesianProductCombinations()
[Test]
public void TestEmptyCartesianEvaluation()
{
using var sequence = Enumerable.Range(0, 5).AsTestingSequence();

var resultA = sequence.Cartesian(Enumerable.Empty<int>(), (a, b) => new { A = a, B = b });
var resultB = Enumerable.Empty<int>().Cartesian(sequence, (a, b) => new { A = a, B = b });
var resultA = Enumerable.Range(0, 5).AsTestingSequence().Cartesian(Enumerable.Empty<int>(), (a, b) => new { A = a, B = b });
var resultB = Enumerable.Empty<int>().Cartesian(Enumerable.Range(0, 5).AsTestingSequence(), (a, b) => new { A = a, B = b });
var resultC = Enumerable.Empty<int>().Cartesian(Enumerable.Empty<int>(), (a, b) => new { A = a, B = b });

Assert.AreEqual(0, resultA.Count());
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89 changes: 2 additions & 87 deletions MoreLinq.Test/MemoizeTest.cs
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Expand Up @@ -183,33 +183,7 @@ public static void MemoizeIsThreadSafe()
}

[Test]
public static void MemoizeRestartsAfterDisposal()
{
var starts = 0;

IEnumerable<int> TestSequence()
{
starts++;
yield return 1;
yield return 2;
}

var memoized = TestSequence().Memoize();

void Run()
{
using ((IDisposable) memoized)
memoized.Take(1).Consume();
}

Run();
Assert.That(starts, Is.EqualTo(1));
Run();
Assert.That(starts, Is.EqualTo(2));
}

[Test]
public static void MemoizeIteratorThrowsWhenCacheDisposedDuringIteration()
public static void MemoizeIteratorThrowsWhenDisposedDuringIteration()
{
var sequence = Enumerable.Range(1, 10);
var memoized = sequence.Memoize();
Expand All @@ -221,7 +195,7 @@ public static void MemoizeIteratorThrowsWhenCacheDisposedDuringIteration()
disposable.Dispose();

var e = Assert.Throws<ObjectDisposedException>(() => reader.Read());
Assert.That(e.ObjectName, Is.EqualTo("MemoizedEnumerable"));
Assert.That(e.ObjectName, Is.EqualTo("MemoizedEnumerable`1"));
}

[Test]
Expand Down Expand Up @@ -259,67 +233,8 @@ IEnumerable<int> TestSequence()
var e2 = Assert.Throws<Exception>(() => r2.Read());
Assert.That(e2, Is.SameAs(error));
}
using (var r1 = memoized.Read())
Assert.That(r1.Read(), Is.EqualTo(123));
}

[Test]
public void MemoizeRethrowsErrorDuringIterationStartToAllIteratorsUntilDisposed()
{
var error = new Exception("This is a test exception.");

var i = 0;
IEnumerable<int> TestSequence()
{
if (0 == i++) // throw at start for first iteration only
throw error;
yield return 42;
}

var xs = new DisposalTrackingSequence<int>(TestSequence());
var memoized = xs.Memoize();
using ((IDisposable) memoized)
using (var r1 = memoized.Read())
using (var r2 = memoized.Read())
{
var e1 = Assert.Throws<Exception>(() => r1.Read());
Assert.That(e1, Is.SameAs(error));

Assert.That(xs.IsDisposed, Is.True);

var e2 = Assert.Throws<Exception>(() => r2.Read());
Assert.That(e2, Is.SameAs(error));
}

using (var r1 = memoized.Read())
using (var r2 = memoized.Read())
Assert.That(r1.Read(), Is.EqualTo(r2.Read()));
}

[Test]
public void MemoizeRethrowsErrorDuringFirstIterationStartToAllIterationsUntilDisposed()
{
var error = new Exception("An error on the first call!");
var obj = new object();
var calls = 0;
var source = Delegate.Enumerable(() => 0 == calls++
? throw error
: Enumerable.Repeat(obj, 1).GetEnumerator());

var memo = source.Memoize();

for (var i = 0; i < 2; i++)
{
var e = Assert.Throws<Exception>(() => memo.First());
Assert.That(e, Is.SameAs(error));
}

((IDisposable) memo).Dispose();
Assert.That(memo.Single(), Is.EqualTo(obj));
}

// TODO Consolidate with MoreLinq.Test.TestingSequence<T>?

sealed class DisposalTrackingSequence<T> : IEnumerable<T>, IDisposable
{
readonly IEnumerable<T> _sequence;
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5 changes: 1 addition & 4 deletions MoreLinq.Test/TestingSequence.cs
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Expand Up @@ -69,14 +69,11 @@ public IEnumerator<T> GetEnumerator()
_disposed = false;
enumerator.Disposed += delegate
{
Assert.That(_disposed, Is.False, "LINQ operators should not dispose a sequence more than once.");
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Per the specification, it is not a failure to call .Dispose() multiple times. The .Dispose() method is expected to be idempotent, such that it is callable multiple times without throwing an exception.

_disposed = true;
};
var ended = false;
enumerator.MoveNextCalled += (_, moved) =>
{
Assert.That(ended, Is.False, "LINQ operators should not continue iterating a sequence that has terminated.");
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Per the specification, it is not a failure to call .MoveNext() after receiving a false response. The enumerator is simply expected to continue to return false for each following call.

ended = !moved;
Assert.That(_disposed, Is.False, "LINQ operators should not call MoveNext() on a disposed sequence.");
MoveNextCallCount++;
};
_sequence = null;
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102 changes: 38 additions & 64 deletions MoreLinq/Experimental/Memoize.cs
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Expand Up @@ -56,106 +56,80 @@ public static IEnumerable<T> Memoize<T>(this IEnumerable<T> source)
switch (source)
{
case null: throw new ArgumentNullException(nameof(source));
case ICollection<T> : // ...
case ICollection<T>: // ...
case IReadOnlyCollection<T>: // ...
case MemoizedEnumerable<T> : return source;
case MemoizedEnumerable<T>: return source;
default: return new MemoizedEnumerable<T>(source);
}
}
}

sealed class MemoizedEnumerable<T> : IEnumerable<T>, IDisposable
{
List<T>? _cache;
readonly List<T> _cache = new();
readonly object _locker;
readonly IEnumerable<T> _source;
IEnumerator<T>? _sourceEnumerator;

readonly Lazy<IEnumerator<T>> _sourceEnumerator;
bool _running = true;
bool _isDisposed = false;

int? _errorIndex;
ExceptionDispatchInfo? _error;

public MemoizedEnumerable(IEnumerable<T> sequence)
{
_source = sequence ?? throw new ArgumentNullException(nameof(sequence));
if (sequence == null) throw new ArgumentNullException(nameof(sequence));
_sourceEnumerator = new Lazy<IEnumerator<T>>(
sequence.GetEnumerator,
System.Threading.LazyThreadSafetyMode.ExecutionAndPublication);
_locker = new object();
}

public IEnumerator<T> GetEnumerator()
{
if (_cache == null)
var index = 0;

while (true)
{
if (_isDisposed)
throw new ObjectDisposedException(GetType().Name);

T current;
lock (_locker)
{
if (_cache == null)
if (index >= _cache.Count)
{
_error?.Throw();
if (index == _errorIndex)
Assume.NotNull(_error).Throw();

bool moved;
try
{
var cache = new List<T>(); // for exception safety, allocate then...
_sourceEnumerator = _source.GetEnumerator(); // (because this can fail)
_cache = cache; // ...commit to state
moved = _running && _sourceEnumerator.Value.MoveNext();
}
catch (Exception ex)
{
_error = ExceptionDispatchInfo.Capture(ex);
_errorIndex = index;
_sourceEnumerator.Value.Dispose();
throw;
}
}
}
}

return _(); IEnumerator<T> _()
{
var index = 0;

while (true)
{
T current;
lock (_locker)
{
if (_cache == null) // Cache disposed during iteration?
throw new ObjectDisposedException(nameof(MemoizedEnumerable<T>));

if (index >= _cache.Count)
if (!moved)
{
if (index == _errorIndex)
Assume.NotNull(_error).Throw();

if (_sourceEnumerator == null)
break;

bool moved;
try
{
moved = _sourceEnumerator.MoveNext();
}
catch (Exception ex)
{
_error = ExceptionDispatchInfo.Capture(ex);
_errorIndex = index;
_sourceEnumerator.Dispose();
_sourceEnumerator = null;
throw;
}

if (moved)
{
_cache.Add(_sourceEnumerator.Current);
}
else
{
_sourceEnumerator.Dispose();
_sourceEnumerator = null;
break;
}
_running = false;
_sourceEnumerator.Value.Dispose();
yield break;
}

current = _cache[index];
_cache.Add(_sourceEnumerator.Value.Current);
}

yield return current;
index++;
current = _cache[index];
}

yield return current;
index++;
}
}

Expand All @@ -166,10 +140,10 @@ public void Dispose()
lock (_locker)
{
_error = null;
_cache = null;
_errorIndex = null;
_sourceEnumerator?.Dispose();
_sourceEnumerator = null;
_sourceEnumerator.Value.Dispose();

_isDisposed = true;
}
}
}
Expand Down