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#nullable enable
using System;
using System.Buffers;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Threading;
namespace Ryujinx.Common.Memory
{
/// <summary>
/// An <see cref="IMemoryOwner{T}"/> implementation with an embedded length and fast <see cref="Span{T}"/>
/// accessor, with memory allocated from <seealso cref="ArrayPool{T}.Shared"/>.
/// </summary>
/// <typeparam name="T">The type of item to store.</typeparam>
public sealed class MemoryOwner<T> : IMemoryOwner<T>
{
private readonly int _length;
private T[]? _array;
/// <summary>
/// Initializes a new instance of the <see cref="MemoryOwner{T}"/> class with the specified parameters.
/// </summary>
/// <param name="length">The length of the new memory buffer to use</param>
private MemoryOwner(int length)
{
_length = length;
_array = ArrayPool<T>.Shared.Rent(length);
}
/// <summary>
/// Creates a new <see cref="MemoryOwner{T}"/> instance with the specified length.
/// </summary>
/// <param name="length">The length of the new memory buffer to use</param>
/// <returns>A <see cref="MemoryOwner{T}"/> instance of the requested length</returns>
/// <exception cref="ArgumentOutOfRangeException">Thrown when <paramref name="length"/> is not valid</exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static MemoryOwner<T> Rent(int length) => new(length);
/// <summary>
/// Creates a new <see cref="MemoryOwner{T}"/> instance with the specified length and the content cleared.
/// </summary>
/// <param name="length">The length of the new memory buffer to use</param>
/// <returns>A <see cref="MemoryOwner{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 MemoryOwner<T> RentCleared(int length)
{
MemoryOwner<T> result = new(length);
result._array.AsSpan(0, length).Clear();
return result;
}
/// <summary>
/// Creates a new <see cref="MemoryOwner{T}"/> instance with the content copied from the specified buffer.
/// </summary>
/// <param name="buffer">The buffer to copy</param>
/// <returns>A <see cref="MemoryOwner{T}"/> instance with the same length and content as <paramref name="buffer"/></returns>
public static MemoryOwner<T> RentCopy(ReadOnlySpan<T> buffer)
{
MemoryOwner<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;
}
/// <inheritdoc/>
public Memory<T> Memory
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get
{
T[]? array = _array;
if (array is null)
{
ThrowObjectDisposedException();
}
return new(array, 0, _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
{
T[]? array = _array;
if (array is null)
{
ThrowObjectDisposedException();
}
ref T firstElementRef = ref MemoryMarshal.GetArrayDataReference(array);
return MemoryMarshal.CreateSpan(ref firstElementRef, _length);
}
}
/// <inheritdoc/>
public void Dispose()
{
T[]? array = Interlocked.Exchange(ref _array, null);
if (array is not null)
{
ArrayPool<T>.Shared.Return(array, RuntimeHelpers.IsReferenceOrContainsReferences<T>());
}
}
/// <summary>
/// Throws an <see cref="ObjectDisposedException"/> when <see cref="_array"/> is <see langword="null"/>.
/// </summary>
[DoesNotReturn]
private static void ThrowObjectDisposedException()
{
throw new ObjectDisposedException(nameof(MemoryOwner<T>), "The buffer has already been disposed.");
}
}
}
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