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Reimplement System.Net.Http's ObjectCollection<T> to reduce allocation / interface dispatch #34902

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Merged
stephentoub merged 1 commit into from
Apr 13, 2020
Merged

Reimplement System.Net.Http's ObjectCollection<T> to reduce allocation / interface dispatch #34902

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42 changes: 4 additions & 38 deletions src/libraries/System.Net.Http/src/System/Net/Http/Headers/CacheControlHeaderValue.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -52,17 +52,7 @@ public bool NoCache
set { _noCache = value; }
}

public ICollection<string> NoCacheHeaders
{
get
{
if (_noCacheHeaders == null)
{
_noCacheHeaders = new ObjectCollection<string>(s_checkIsValidToken);
}
return _noCacheHeaders;
}
}
public ICollection<string> NoCacheHeaders => _noCacheHeaders ??= new ObjectCollection<string>(s_checkIsValidToken);

public bool NoStore
{
Expand Down Expand Up @@ -124,17 +114,7 @@ public bool Private
set { _privateField = value; }
}

public ICollection<string> PrivateHeaders
{
get
{
if (_privateHeaders == null)
{
_privateHeaders = new ObjectCollection<string>(s_checkIsValidToken);
}
return _privateHeaders;
}
}
public ICollection<string> PrivateHeaders => _privateHeaders ??= new ObjectCollection<string>(s_checkIsValidToken);

public bool MustRevalidate
{
Expand All @@ -148,17 +128,7 @@ public bool ProxyRevalidate
set { _proxyRevalidate = value; }
}

public ICollection<NameValueHeaderValue> Extensions
{
get
{
if (_extensions == null)
{
_extensions = new ObjectCollection<NameValueHeaderValue>();
}
return _extensions;
}
}
public ICollection<NameValueHeaderValue> Extensions => _extensions ??= new ObjectCollection<NameValueHeaderValue>();

public CacheControlHeaderValue()
{
Expand Down Expand Up @@ -604,11 +574,7 @@ private static bool TrySetOptionalTokenList(NameValueHeaderValue nameValue, ref
return false;
}

if (destination == null)
{
destination = new ObjectCollection<string>(s_checkIsValidToken);
}

destination ??= new ObjectCollection<string>(s_checkIsValidToken);
destination.Add(valueString.Substring(current, tokenLength));

current = current + tokenLength;
Expand Down
12 changes: 1 addition & 11 deletions src/libraries/System.Net.Http/src/System/Net/Http/Headers/ContentDispositionHeaderValue.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -40,17 +40,7 @@ public string DispositionType
}
}

public ICollection<NameValueHeaderValue> Parameters
{
get
{
if (_parameters == null)
{
_parameters = new ObjectCollection<NameValueHeaderValue>();
}
return _parameters;
}
}
public ICollection<NameValueHeaderValue> Parameters => _parameters ??= new ObjectCollection<NameValueHeaderValue>();

public string? Name
{
Expand Down
12 changes: 1 addition & 11 deletions src/libraries/System.Net.Http/src/System/Net/Http/Headers/MediaTypeHeaderValue.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -55,17 +55,7 @@ public string? CharSet
}
}

public ICollection<NameValueHeaderValue> Parameters
{
get
{
if (_parameters == null)
{
_parameters = new ObjectCollection<NameValueHeaderValue>();
}
return _parameters;
}
}
public ICollection<NameValueHeaderValue> Parameters => _parameters ??= new ObjectCollection<NameValueHeaderValue>();

[DisallowNull]
public string? MediaType
Expand Down
12 changes: 1 addition & 11 deletions ...braries/System.Net.Http/src/System/Net/Http/Headers/NameValueWithParametersHeaderValue.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,17 +18,7 @@ public class NameValueWithParametersHeaderValue : NameValueHeaderValue, ICloneab

private ObjectCollection<NameValueHeaderValue>? _parameters;

public ICollection<NameValueHeaderValue> Parameters
{
get
{
if (_parameters == null)
{
_parameters = new ObjectCollection<NameValueHeaderValue>();
}
return _parameters;
}
}
public ICollection<NameValueHeaderValue> Parameters => _parameters ??= new ObjectCollection<NameValueHeaderValue>();

public NameValueWithParametersHeaderValue(string name)
: base(name)
Expand Down
207 changes: 181 additions & 26 deletions src/libraries/System.Net.Http/src/System/Net/Http/Headers/ObjectCollection.cs
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Expand Up @@ -2,57 +2,212 @@
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics;

namespace System.Net.Http.Headers
{
// We need to prevent 'null' values in the collection. Since List<T> allows them, we will create
// a custom collection class. It is less efficient than List<T> but only used for small collections.
internal sealed class ObjectCollection<T> : Collection<T> where T : class
/// <summary>An <see cref="ICollection{T}"/> list that prohibits null elements and that is optimized for a small number of elements.</summary>
[DebuggerDisplay("Count = {Count}")]
[DebuggerTypeProxy(nameof(DebugView))]
internal sealed class ObjectCollection<T> : ICollection<T> where T : class
{
private static readonly Action<T> s_defaultValidator = CheckNotNull;
private const int DefaultSize = 4;

private readonly Action<T> _validator;
/// <summary>Optional delegate used to validate added items.</summary>
private readonly Action<T>? _validator;
/// <summary>null, a T, or a T[].</summary>
internal object? _items;
/// <summary>Number of elements stored in the collection.</summary>
internal int _size;

public ObjectCollection()
: this(s_defaultValidator)
public ObjectCollection() { }

public ObjectCollection(Action<T> validator) => _validator = validator;

public int Count => _size;

public bool IsReadOnly => false;

public void Add(T item)
{
// Validate the item, either just by checking it for null, or using a custom validator,
// which should also check for null.
if (_validator is null)
{
if (item is null)
{
throw new ArgumentNullException(nameof(item));
}
}
else
{
_validator.Invoke(item);
Debug.Assert(item != null);
}

if (_items is null)
{
// The collection is empty. Just store the new item directly.
_items = item;
_size = 1;
}
else if (_items is T existingItem)
{
// The collection has a single item stored directly. Upgrade to
// an array, and store both the existing and new items.
Debug.Assert(_size == 1);
T[] items = new T[DefaultSize];
items[0] = existingItem;
items[1] = item;
_items = items;
_size = 2;
}
else
{
T[] array = (T[])_items;
int size = _size;
if ((uint)size < (uint)array.Length)
{
// There's room in the existing array. Add the item.
array[size] = item;
}
else
{
// We need to grow the array. Do so, and store the new item.
Debug.Assert(_size > 0);
Debug.Assert(_size == array.Length);

var newItems = new T[array.Length * 2];
Array.Copy(array, newItems, size);
_items = newItems;
newItems[size] = item;
}
_size = size + 1;
}
}

public ObjectCollection(Action<T> validator)
: base(new List<T>())
public void Clear()
{
Debug.Assert(validator != null, $"{nameof(validator)} must not be null.");
_validator = validator;
_items = null;
_size = 0;
}

// This is only used internally to enumerate the collection
// without the enumerator allocation.
public new List<T>.Enumerator GetEnumerator()
public bool Contains(T item) =>
ReferenceEquals(item, _items) ||
(_size != 0 && _items is T[] items && Array.IndexOf(items, item, 0, _size) != -1);

public void CopyTo(T[] array, int arrayIndex)
{
return ((List<T>)Items).GetEnumerator();
if (_items is T[] items)
{
Array.Copy(items, 0, array, arrayIndex, _size);
}
else
{
Debug.Assert(_size == 0 || _size == 1);
if (array is null || _size > array.Length - arrayIndex)
{
// Use Array.CopyTo to throw the right exceptions.
new T[] { (T)_items! }.CopyTo(array!, arrayIndex);
}
else if (_size == 1)
{
array[arrayIndex] = (T)_items!;
}
}
}

protected override void InsertItem(int index, T item)
public bool Remove(T item)
{
_validator(item);
base.InsertItem(index, item);
if (ReferenceEquals(_items, item))
{
_items = null;
_size = 0;
return true;
}

if (_items is T[] items)
{
int index = Array.IndexOf(items, item, 0, _size);
if (index != -1)
{
_size--;
if (index < _size)
{
Array.Copy(items, index + 1, items, index, _size - index);
}
items[_size] = null!;

return true;
}
}

return false;
}

protected override void SetItem(int index, T item)
public Enumerator GetEnumerator() => new Enumerator(this);
IEnumerator<T> IEnumerable<T>.GetEnumerator() => GetEnumerator();
IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

public struct Enumerator : IEnumerator<T>
{
_validator(item);
base.SetItem(index, item);
private readonly ObjectCollection<T> _list;
private int _index;
private T _current;

internal Enumerator(ObjectCollection<T> list)
{
_list = list;
_index = 0;
_current = default!;
}

public void Dispose() { }

public bool MoveNext()
{
ObjectCollection<T> list = _list;

if ((uint)_index < (uint)list._size)
{
_current = list._items is T[] items ? items[_index] : (T)list._items!;
_index++;
return true;
}

_index = _list._size + 1;
_current = default!;
return false;
}

public T Current => _current!;

object? IEnumerator.Current => _current;

void IEnumerator.Reset()
{
_index = 0;
_current = default!;
}
}

private static void CheckNotNull(T item)
internal sealed class DebugView
{
// Null values cannot be added to the collection.
if (item == null)
private readonly ObjectCollection<T> _collection;

public DebugView(ObjectCollection<T> collection) => _collection = collection ?? throw new ArgumentNullException(nameof(collection));

[DebuggerBrowsable(DebuggerBrowsableState.RootHidden)]
public T[] Items
{
throw new ArgumentNullException(nameof(item));
get
{
T[] items = new T[_collection.Count];
_collection.CopyTo(items, 0);
return items;
}
}
}
}
Expand Down
12 changes: 1 addition & 11 deletions src/libraries/System.Net.Http/src/System/Net/Http/Headers/RangeHeaderValue.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,17 +25,7 @@ public string Unit
}
}

public ICollection<RangeItemHeaderValue> Ranges
{
get
{
if (_ranges == null)
{
_ranges = new ObjectCollection<RangeItemHeaderValue>();
}
return _ranges;
}
}
public ICollection<RangeItemHeaderValue> Ranges => _ranges ??= new ObjectCollection<RangeItemHeaderValue>();

public RangeHeaderValue()
{
Expand Down
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