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Zero/ZeroLevel/Services/Pools/ObjectPool.cs

164 lines
5.4 KiB

using System;
using System.Diagnostics;
using System.Threading;
namespace ZeroLevel.Services.Pools
{
/// <summary>
/// Steal from Roslyn
/// https://github.com/dotnet/roslyn/blob/master/src/Dependencies/PooledObjects/ObjectPool%601.cs
/// </summary>
public class ObjectPool<T> where T : class
{
[DebuggerDisplay("{Value,nq}")]
private struct Element
{
internal T Value;
}
/// <remarks>
/// Not using System.Func{T} because this file is linked into the (debugger) Formatter,
/// which does not have that type (since it compiles against .NET 2.0).
/// </remarks>
public delegate T Factory();
// Storage for the pool objects. The first item is stored in a dedicated field because we
// expect to be able to satisfy most requests from it.
private T _firstItem;
private readonly Element[] _items;
// factory is stored for the lifetime of the pool. We will call this only when pool needs to
// expand. compared to "new T()", Func gives more flexibility to implementers and faster
// than "new T()".
private readonly Factory _factory;
public ObjectPool(Factory factory)
: this(factory, Environment.ProcessorCount * 2)
{ }
public ObjectPool(Factory factory, int size)
{
Debug.Assert(size >= 1);
_factory = factory;
_items = new Element[size - 1];
}
private T CreateInstance()
{
var inst = _factory();
return inst;
}
/// <summary>
/// Produces an instance.
/// </summary>
/// <remarks>
/// Search strategy is a simple linear probing which is chosen for it cache-friendliness.
/// Note that Free will try to store recycled objects close to the start thus statistically
/// reducing how far we will typically search.
/// </remarks>
public T Allocate()
{
// PERF: Examine the first element. If that fails, AllocateSlow will look at the remaining elements.
// Note that the initial read is optimistically not synchronized. That is intentional.
// We will interlock only when we have a candidate. in a worst case we may miss some
// recently returned objects. Not a big deal.
T inst = _firstItem;
if (inst == null || inst != Interlocked.CompareExchange(ref _firstItem, null, inst))
{
inst = AllocateSlow();
}
return inst;
}
private T AllocateSlow()
{
var items = _items;
for (int i = 0; i < items.Length; i++)
{
// Note that the initial read is optimistically not synchronized. That is intentional.
// We will interlock only when we have a candidate. in a worst case we may miss some
// recently returned objects. Not a big deal.
T inst = items[i].Value;
if (inst != null)
{
if (inst == Interlocked.CompareExchange(ref items[i].Value, null, inst))
{
return inst;
}
}
}
return CreateInstance();
}
/// <summary>
/// Returns objects to the pool.
/// </summary>
/// <remarks>
/// Search strategy is a simple linear probing which is chosen for it cache-friendliness.
/// Note that Free will try to store recycled objects close to the start thus statistically
/// reducing how far we will typically search in Allocate.
/// </remarks>
public void Free(T obj)
{
if (!Validate(obj))
{
return;
}
if (_firstItem == null)
{
// Intentionally not using interlocked here.
// In a worst case scenario two objects may be stored into same slot.
// It is very unlikely to happen and will only mean that one of the objects will get collected.
_firstItem = obj;
}
else
{
FreeSlow(obj);
}
}
private void FreeSlow(T obj)
{
var items = _items;
for (int i = 0; i < items.Length; i++)
{
if (items[i].Value == null)
{
// Intentionally not using interlocked here.
// In a worst case scenario two objects may be stored into same slot.
// It is very unlikely to happen and will only mean that one of the objects will get collected.
items[i].Value = obj;
break;
}
}
}
private bool Validate(object obj)
{
if (obj == null) return false;
if (_firstItem == obj) return false;
var items = _items;
for (int i = 0; i < items.Length; i++)
{
var value = items[i].Value;
if (value == null)
{
return true;
}
if (value == obj) return false;
}
return true;
}
}
/*
Alternate
https://stackoverflow.com/questions/1698738/objectpoolt-or-similar-for-net-already-in-a-library
*/
}

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