.NET使用Collections.Pooled提升性能优化的方法

Install-Package Collections.Pooled
dotnet add package Collections.Pooled
paket add Collections.Pooled

using Collections.Pooled;
// 使用方式是一样的
var list = new List<int>();
var pooledList = new PooledList<int>();
var dictionary = new Dictionary<int,int>();
var pooledDictionary = new PooledDictionary<int,int>();
// 包括PooledSet、PooledQueue、PooledStack的使用方法都是一样的
var pooledList1 = Enumerable.Range(0,100).ToPooledList();
var pooledDictionary1 = Enumerable.Range(0,100).ToPooledDictionary(i => i, i => i);

using Collections.Pooled;
// 使用using var 会在pooled对象使用完毕后自动释放
using var pooledList = new PooledList<int>();
Console.WriteLine(pooledList.Count);
// 使用using作用域 作用域结束以后就会释放
using (var pooledDictionary = new PooledDictionary<int, int>())
{
	Console.WriteLine(pooledDictionary.Count);
}
// 手动调用Dispose方法
var pooledStack = new PooledStack<int>();
Console.WriteLine(pooledStack.Count);
pooledList.Dispose();

namespace Collections.Pooled
{
    /// <summary>
    /// 这个枚举允许控制在内部数组返回到ArrayPool时如何处理数据。
    /// 数组返回到ArrayPool时如何处理数据。在使用默认选项之外的其他选项之前，请注意了解 
    /// 在使用默认值Auto之外的任何其他选项之前，请仔细了解每个选项的作用。
    /// </summary>
    public enum ClearMode
    {
        /// <summary>
        /// <para><code>Auto</code>根据目标框架有不同的行为</para>
        /// <para>.NET Core 2.1: 引用类型和包含引用类型的值类型在内部数组返回池时被清除。 不包含引用类型的值类型在返回池时不会被清除。</para>
        /// <para>.NET Standard 2.0: 在返回池之前清除所有用户类型，以防它们包含引用类型。 对于 .NET Standard，Auto 和 Always 具有相同的行为。</para>
        /// </summary>
        Auto = 0,
        
        /// <summary>
        /// The <para><code>Always</code> 设置的效果是在返回池之前总是清除用户类型。
        /// </summary>
        Always = 1,
        
        /// <summary>
        /// <para><code>Never</code> 将导致池化集合在将它们返回池之前永远不会清除用户类型。</para>
        /// </summary>
        Never = 2
    }
}

private static readonly string[] List = Enumerable  
    .Range(0, 10000).Select(c => c.ToString()).ToArray();  
// 使用默认的集合类型  
[Benchmark(Baseline = true)]  
public int UseList()  
{  
    var list = new List<string>(1024);  
    for (var index = 0; index < List.Length; index++)  
    {  
        var item = List[index];  
        list.Add(item);  
    }  
    return list.Count;  
}  
// 使用PooledList 并且及时释放  
[Benchmark]  
public int UsePooled()  
{  
    using var list = new PooledList<string>(1024);  
    for (var index = 0; index < List.Length; index++)  
    {  
        var item = List[index];  
        list.Add(item);  
    }  
    return list.Count;  
}  
// 使用PooledList 不释放  
[Benchmark]  
public int UsePooledWithOutUsing()  
{  
    var list = new PooledList<string>(1024);  
    for (var index = 0; index < List.Length; index++)  
    {  
        var item = List[index];  
        list.Add(item);  
    }  
    return list.Count;  
}

public List(int capacity)
{
      if (capacity < 0)
          ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.capacity, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);

      if (capacity == 0)
          _items = s_emptyArray;
      else
          _items = new T[capacity];
}

// 默认使用ArrayPool<T>.Shared池
public PooledList(int capacity, ClearMode clearMode, bool sizeToCapacity) : this(capacity, clearMode, ArrayPool<T>.Shared, sizeToCapacity) { }  

// 分配数组使用 ArrayPool
public PooledList(int capacity, ClearMode clearMode, ArrayPool<T> customPool, bool sizeToCapacity)
{
    if (capacity < 0)
        ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.capacity, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
    _pool = customPool ?? ArrayPool<T>.Shared;
    _clearOnFree = ShouldClear(clearMode);
    if (capacity == 0)
    {
        _items = s_emptyArray;
    }
    else
    {
        _items = _pool.Rent(capacity);
    }
    
    if (sizeToCapacity)
    {
        _size = capacity;
        if (clearMode != ClearMode.Never)
        {
            Array.Clear(_items, 0, _size);
        }
    }
 }

public int Capacity
{
    get => _items.Length;
    set
    {
        if (value < _size)
        {
            ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.value, ExceptionResource.ArgumentOutOfRange_SmallCapacity);
        }

        if (value != _items.Length)
        {
            if (value > 0)
            {
                // 从池中分配数组
                var newItems = _pool.Rent(value);
                if (_size > 0)
                {
                    Array.Copy(_items, newItems, _size);
                }
                // 旧数组归还到池中
                ReturnArray();
                _items = newItems;
            }
            else
            {
                ReturnArray();
                _size = 0;
            }
        }
    }
}
private void ReturnArray()  
{  
    if (_items.Length == 0)  
        return;  
    try  
    {  
        // 归还到池中
        _pool.Return(_items, clearArray: _clearOnFree);  
    }  
    catch (ArgumentException)  
    {  
        // ArrayPool可能会抛出异常，我们直接吞掉 
    }  
    _items = s_emptyArray;  
}