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DefaultObjectPool.cs
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DefaultObjectPool.cs
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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System;
using System.Collections.Concurrent;
using System.Threading;
namespace Microsoft.Extensions.ObjectPool;
/// <summary>
/// Default implementation of <see cref="ObjectPool{T}"/>.
/// </summary>
/// <typeparam name="T">The type to pool objects for.</typeparam>
/// <remarks>This implementation keeps a cache of retained objects. This means that if objects are returned when the pool has already reached "maximumRetained" objects they will be available to be Garbage Collected.</remarks>
public class DefaultObjectPool<T> : ObjectPool<T> where T : class
{
private readonly Func<T> _createFunc;
private readonly Func<T, bool> _returnFunc;
private readonly int _maxCapacity;
private int _numItems;
private protected readonly ConcurrentQueue<T> _items = new();
private protected T? _fastItem;
/// <summary>
/// Creates an instance of <see cref="DefaultObjectPool{T}"/>.
/// </summary>
/// <param name="policy">The pooling policy to use.</param>
public DefaultObjectPool(IPooledObjectPolicy<T> policy)
: this(policy, Environment.ProcessorCount * 2)
{
}
/// <summary>
/// Creates an instance of <see cref="DefaultObjectPool{T}"/>.
/// </summary>
/// <param name="policy">The pooling policy to use.</param>
/// <param name="maximumRetained">The maximum number of objects to retain in the pool.</param>
public DefaultObjectPool(IPooledObjectPolicy<T> policy, int maximumRetained)
{
// cache the target interface methods, to avoid interface lookup overhead
_createFunc = policy.Create;
_returnFunc = policy.Return;
_maxCapacity = maximumRetained - 1; // -1 to account for _fastItem
}
/// <inheritdoc />
public override T Get()
{
var item = _fastItem;
if (item == null || Interlocked.CompareExchange(ref _fastItem, null, item) != item)
{
if (_items.TryDequeue(out item))
{
Interlocked.Decrement(ref _numItems);
return item;
}
// no object available, so go get a brand new one
return _createFunc();
}
return item;
}
/// <inheritdoc />
public override void Return(T obj)
{
ReturnCore(obj);
}
/// <summary>
/// Returns an object to the pool.
/// </summary>
/// <returns>true if the object was returned to the pool</returns>
private protected bool ReturnCore(T obj)
{
if (!_returnFunc(obj))
{
// policy says to drop this object
return false;
}
if (_fastItem != null || Interlocked.CompareExchange(ref _fastItem, obj, null) != null)
{
if (Interlocked.Increment(ref _numItems) <= _maxCapacity)
{
_items.Enqueue(obj);
return true;
}
// no room, clean up the count and drop the object on the floor
Interlocked.Decrement(ref _numItems);
return false;
}
return true;
}
}