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using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Threading;
namespace Ryujinx.Graphics.GAL.Multithreading.Model
{
/// <summary>
/// A memory pool for passing through Span<T> resources with one producer and consumer.
/// Data is copied on creation to part of the pool, then that region is reserved until it is disposed by the consumer.
/// Similar to the command queue, this pool assumes that data is created and disposed in the same order.
/// </summary>
class CircularSpanPool
{
private readonly ThreadedRenderer _renderer;
private readonly byte[] _pool;
private readonly int _size;
private int _producerPtr;
private int _producerSkipPosition = -1;
private int _consumerPtr;
public CircularSpanPool(ThreadedRenderer renderer, int size)
{
_renderer = renderer;
_size = size;
_pool = new byte[size];
}
public SpanRef<T> Insert<T>(ReadOnlySpan<T> data) where T : unmanaged
{
int size = data.Length * Unsafe.SizeOf<T>();
// Wrapping aware circular queue.
// If there's no space at the end of the pool for this span, we can't fragment it.
// So just loop back around to the start. Remember the last skipped position.
bool wraparound = _producerPtr + size >= _size;
int index = wraparound ? 0 : _producerPtr;
// _consumerPtr is from another thread, and we're taking it without a lock, so treat this as a snapshot in the past.
// We know that it will always be before or equal to the producer pointer, and it cannot pass it.
// This is enough to reason about if there is space in the queue for the data, even if we're checking against an outdated value.
int consumer = _consumerPtr;
bool beforeConsumer = _producerPtr < consumer;
if (size > _size - 1 || (wraparound && beforeConsumer) || ((index < consumer || wraparound) && index + size >= consumer))
{
// Just get an array in the following situations:
// - The data is too large to fit in the pool.
// - A wraparound would happen but the consumer would be covered by it.
// - The producer would catch up to the consumer as a result.
return new SpanRef<T>(_renderer, data.ToArray());
}
data.CopyTo(MemoryMarshal.Cast<byte, T>(new Span<byte>(_pool).Slice(index, size)));
if (wraparound)
{
_producerSkipPosition = _producerPtr;
}
_producerPtr = index + size;
return new SpanRef<T>(data.Length);
}
public Span<T> Get<T>(int length) where T : unmanaged
{
int size = length * Unsafe.SizeOf<T>();
if (_consumerPtr == Interlocked.CompareExchange(ref _producerSkipPosition, -1, _consumerPtr))
{
_consumerPtr = 0;
}
return MemoryMarshal.Cast<byte, T>(new Span<byte>(_pool).Slice(_consumerPtr, size));
}
public void Dispose<T>(int length) where T : unmanaged
{
int size = length * Unsafe.SizeOf<T>();
_consumerPtr += size;
}
}
}
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