StitchATon2/Infra/Buffers/ImmovableMemory.cs

using System.Buffers;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace StitchATon2.Infra.Buffers;

internal sealed unsafe class ImmovableMemory<T> : MemoryManager<T>, IBuffer<T> where T : unmanaged
{
    internal readonly T* Pointer;
    private bool _disposed;

    public ImmovableMemory(int length)
    {
        Pointer = (T*)NativeMemory.Alloc((nuint)length, (nuint)Unsafe.SizeOf<T>());
        Length = length;
    }
    
    protected override void Dispose(bool disposing)
    {
        if (_disposed) return;
        NativeMemory.Free(Pointer);
        _disposed = true;
    }

    public override Span<T> GetSpan()
        => _disposed 
            ? throw new ObjectDisposedException(nameof(ImmovableMemory<T>)) 
            : new Span<T>(Pointer, Length);

    public override MemoryHandle Pin(int elementIndex = 0)
        => _disposed
            ? throw new ObjectDisposedException(nameof(ImmovableMemory<T>))
            : new MemoryHandle(Pointer + elementIndex);

    public override void Unpin()
    {
    }

    public ref T this[int index]
    {
        get
        {
            if (_disposed) throw new ObjectDisposedException(nameof(ImmovableMemory<T>));
            return ref Unsafe.AsRef<T>(Pointer + index);
        }
    }

    public Span<T> Span => GetSpan();
    
    public int Length { get; }
}