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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.
// See the LICENSE file in the project root for more information.
using System.Threading;
namespace System.Runtime.InteropServices
{
/// <summary>
/// Allows limited thread safe reuse of heap buffers to limit memory pressure.
///
/// This cache does not ensure that multiple copies of handles are not released back into the cache.
/// </summary>
internal sealed class SafeHeapHandleCache : IDisposable
{
private readonly ulong _minSize;
private readonly ulong _maxSize;
// internal for testing
internal readonly SafeHeapHandle[] _handleCache;
/// <param name="minSize">Smallest buffer size to allocate in bytes.</param>
/// <param name="maxSize">The largest buffer size to cache in bytes.</param>
/// <param name="maxHandles">The maximum number of handles to cache.</param>
public SafeHeapHandleCache(ulong minSize = 64, ulong maxSize = 1024 * 2, int maxHandles = 0)
{
_minSize = minSize;
_maxSize = maxSize;
_handleCache = new SafeHeapHandle[maxHandles > 0 ? maxHandles : Environment.ProcessorCount * 4];
}
/// <summary>
/// Get a HeapHandle
/// </summary>
public SafeHeapHandle Acquire(ulong minSize = 0)
{
if (minSize < _minSize) minSize = _minSize;
SafeHeapHandle handle = null;
for (int i = 0; i < _handleCache.Length; i++)
{
handle = Interlocked.Exchange(ref _handleCache[i], null);
if (handle != null) break;
}
if (handle != null)
{
// One possible future consideration is to attempt cycling through to
// find one that might already have sufficient capacity
if (handle.ByteLength < minSize)
handle.Resize(minSize);
}
else
{
handle = new SafeHeapHandle(minSize);
}
return handle;
}
/// <summary>
/// Give a HeapHandle back for potential reuse
/// </summary>
public void Release(SafeHeapHandle handle)
{
if (handle.ByteLength <= _maxSize)
{
for (int i = 0; i < _handleCache.Length; i++)
{
// Push the handles down, walking the last one off the end to keep
// the top of the "stack" fresh
handle = Interlocked.Exchange(ref _handleCache[i], handle);
if (handle == null) return;
}
}
handle.Dispose();
}
public void Dispose()
{
Dispose(disposing: true);
}
private void Dispose(bool disposing)
{
if (disposing && _handleCache != null)
{
foreach (SafeHeapHandle handle in _handleCache)
{
if (handle != null) handle.Dispose();
}
}
}
}
}
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