New pooled memory types (#6821)

* feat: add new types MemoryOwner and SpanOwner

* use SpanOwner instead of new array allocation

* change for loop condition to `fences.Length` instead of `count` to elide Span boundary checks on `fences`

src/Ryujinx.Common/Memory/MemoryOwner.cs

@@ -0,0 +1,140 @@
+#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);
+            }
+        }
+
+        /// <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.");
+        }
+    }
+}