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using System;
using System.Buffers;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
namespace Ryujinx.Common.Memory
{
/// <summary>
/// A stack-only type that rents a buffer of a specified length from <seealso cref="ArrayPool{T}.Shared"/>.
/// It does not implement <see cref="IDisposable"/> to avoid being boxed, but should still be disposed. This
/// is easy since C# 8, which allows use of C# `using` constructs on any type that has a public Dispose() method.
/// To keep this type simple, fast, and read-only, it does not check or guard against multiple disposals.
/// For all these reasons, all usage should be with a `using` block or statement.
/// </summary>
/// <typeparam name="T">The type of item to store.</typeparam>
public readonly ref struct SpanOwner<T>
{
private readonly int _length;
private readonly T[] _array;
/// <summary>
/// Initializes a new instance of the <see cref="SpanOwner{T}"/> struct with the specified parameters.
/// </summary>
/// <param name="length">The length of the new memory buffer to use</param>
private SpanOwner(int length)
{
_length = length;
_array = ArrayPool<T>.Shared.Rent(length);
}
/// <summary>
/// Gets an empty <see cref="SpanOwner{T}"/> instance.
/// </summary>
public static SpanOwner<T> Empty
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get => new(0);
}
/// <summary>
/// Creates a new <see cref="SpanOwner{T}"/> instance with the specified length.
/// </summary>
/// <param name="length">The length of the new memory buffer to use</param>
/// <returns>A <see cref="SpanOwner{T}"/> instance of the requested length</returns>
/// <exception cref="ArgumentOutOfRangeException">Thrown when <paramref name="length"/> is not valid</exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static SpanOwner<T> Rent(int length) => new(length);
/// <summary>
/// Creates a new <see cref="SpanOwner{T}"/> instance with the length and the content cleared.
/// </summary>
/// <param name="length">The length of the new memory buffer to use</param>
/// <returns>A <see cref="SpanOwner{T}"/> instance of the requested length and the content cleared</returns>
/// <exception cref="ArgumentOutOfRangeException">Thrown when <paramref name="length"/> is not valid</exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static SpanOwner<T> RentCleared(int length)
{
SpanOwner<T> result = new(length);
result._array.AsSpan(0, length).Clear();
return result;
}
/// <summary>
/// Creates a new <see cref="SpanOwner{T}"/> instance with the content copied from the specified buffer.
/// </summary>
/// <param name="buffer">The buffer to copy</param>
/// <returns>A <see cref="SpanOwner{T}"/> instance with the same length and content as <paramref name="buffer"/></returns>
public static SpanOwner<T> RentCopy(ReadOnlySpan<T> buffer)
{
SpanOwner<T> result = new(buffer.Length);
buffer.CopyTo(result._array);
return result;
}
/// <summary>
/// Gets the number of items in the current instance
/// </summary>
public int Length
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get => _length;
}
/// <summary>
/// Gets a <see cref="Span{T}"/> wrapping the memory belonging to the current instance.
/// </summary>
/// <remarks>
/// Uses a trick made possible by the .NET 6+ runtime array layout.
/// </remarks>
public Span<T> Span
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get
{
ref T firstElementRef = ref MemoryMarshal.GetArrayDataReference(_array);
return MemoryMarshal.CreateSpan(ref firstElementRef, _length);
}
}
/// <summary>
/// Implements the duck-typed <see cref="IDisposable.Dispose"/> method.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public void Dispose()
{
ArrayPool<T>.Shared.Return(_array);
}
}
}
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