initial skeleton of discontinuous buffer object model

src/ImageSharp/ImageSharp.csproj

@@ -25,9 +25,9 @@
   </ItemGroup>
 
   <ItemGroup Condition=" $(TargetFramework.StartsWith('netstandard')) OR '$(TargetFramework)' == 'net472'">
-    <PackageReference Include="System.Numerics.Vectors"/>
-    <PackageReference Include="System.Buffers"/>
-    <PackageReference Include="System.Memory"/>
+    <PackageReference Include="System.Numerics.Vectors" />
+    <PackageReference Include="System.Buffers" />
+    <PackageReference Include="System.Memory" />
   </ItemGroup>
 
   <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard1.3'">

src/ImageSharp/Memory/Allocators/ArrayPoolMemoryAllocator.cs

@@ -89,6 +89,14 @@ namespace SixLabors.ImageSharp.Memory
             this.InitArrayPools();
         }
 
+        /// <summary>
+        /// Gets or sets the length of the largest contiguous buffer that can be handled by this allocator instance.
+        /// </summary>
+        public int MaximumContiguousBufferLength { get; set; } = Int32.MaxValue;
+
+        /// <inheritdoc />
+        protected internal override int GetMaximumContiguousBufferLength() => this.MaximumContiguousBufferLength;
+
         /// <inheritdoc />
         public override IMemoryOwner<T> Allocate<T>(int length, AllocationOptions options = AllocationOptions.None)
         {
@@ -147,4 +155,4 @@ namespace SixLabors.ImageSharp.Memory
             this.normalArrayPool = ArrayPool<byte>.Create(this.PoolSelectorThresholdInBytes, this.maxArraysPerBucketNormalPool);
         }
     }
-}
+}

src/ImageSharp/Memory/Allocators/MemoryAllocator.cs

@@ -10,6 +10,11 @@ namespace SixLabors.ImageSharp.Memory
     /// </summary>
     public abstract class MemoryAllocator
     {
+        /// <summary>
+        /// Gets the length of the largest contiguous buffer that can be handled by this allocator instance.
+        /// </summary>
+        protected internal abstract int GetMaximumContiguousBufferLength();
+
         /// <summary>
         /// Allocates an <see cref="IMemoryOwner{T}" />, holding a <see cref="System.Memory{T}"/> of length <paramref name="length"/>.
         /// </summary>

src/ImageSharp/Memory/Allocators/SimpleGcMemoryAllocator.cs

@@ -11,6 +11,9 @@ namespace SixLabors.ImageSharp.Memory
     /// </summary>
     public sealed class SimpleGcMemoryAllocator : MemoryAllocator
     {
+        /// <inheritdoc />
+        protected internal override int GetMaximumContiguousBufferLength() => int.MaxValue;
+
         /// <inheritdoc />
         public override IMemoryOwner<T> Allocate<T>(int length, AllocationOptions options = AllocationOptions.None)
         {
@@ -27,4 +30,4 @@ namespace SixLabors.ImageSharp.Memory
             return new BasicByteBuffer(new byte[length]);
         }
     }
-}
+}

src/ImageSharp/Memory/BufferArea{T}.cs

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Memory
     /// Represents a rectangular area inside a 2D memory buffer (<see cref="Buffer2D{T}"/>).
     /// This type is kind-of 2D Span, but it can live on heap.
     /// </summary>
-    /// <typeparam name="T">The element type</typeparam>
+    /// <typeparam name="T">The element type.</typeparam>
     internal readonly struct BufferArea<T>
         where T : struct
     {

src/ImageSharp/Memory/DiscontinuousProto/IUniformMemoryGroup{T}.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Collections.Generic;
+
+namespace SixLabors.ImageSharp.Memory.DiscontinuousProto
+{
+    /// <summary>
+    /// Represents a group of one or more uniformly-sized discontinuous memory segments.
+    /// The last segment can be smaller than the preceding ones.
+    /// </summary>
+    /// <typeparam name="T">The element type.</typeparam>
+    public interface IUniformMemoryGroup<T> : IReadOnlyList<Memory<T>> where T : struct
+    {
+        bool IsValid { get; }
+    }
+}

src/ImageSharp/Memory/DiscontinuousProto/InvalidMemoryOperationException.cs

@@ -0,0 +1,8 @@
+using System;
+
+namespace SixLabors.ImageSharp.Memory.DiscontinuousProto
+{
+    public class InvalidMemoryOperationException : InvalidOperationException
+    {
+    }
+}

src/ImageSharp/Memory/DiscontinuousProto/UniformMemoryGroupView{T}.cs

@@ -0,0 +1,76 @@
+using System;
+using System.Buffers;
+using System.Collections;
+using System.Collections.Generic;
+
+namespace SixLabors.ImageSharp.Memory.DiscontinuousProto
+{
+    /// <summary>
+    /// Implements <see cref="IUniformMemoryGroup{T}"/>, defining a view for <see cref="UniformMemoryGroup{T}"/>
+    /// rather than owning the segments.
+    /// </summary>
+    /// <remarks>
+    /// This type provides an indirection, protecting the users of publicly exposed memory API-s
+    /// from internal memory-swaps. Whenever an internal swap happens, the <see cref="UniformMemoryGroupView{T}"/>
+    /// instance becomes invalid, throwing an exception on all operations.
+    /// </remarks>
+    /// <typeparam name="T">The element type.</typeparam>
+    public class UniformMemoryGroupView<T> : IUniformMemoryGroup<T> where T : struct
+    {
+        private readonly UniformMemoryGroup<T> owner;
+        private readonly MemoryOwnerWrapper[] memoryWrappers;
+
+        public UniformMemoryGroupView(UniformMemoryGroup<T> owner)
+        {
+            this.IsValid = true;
+            this.owner = owner;
+            this.memoryWrappers = new MemoryOwnerWrapper[owner.Count];
+
+            for (int i = 0; i < owner.Count; i++)
+            {
+                this.memoryWrappers[i] = new MemoryOwnerWrapper(this, i);
+            }
+        }
+
+        public IEnumerator<Memory<T>> GetEnumerator() => throw new NotImplementedException();
+
+        IEnumerator IEnumerable.GetEnumerator() => this.GetEnumerator();
+
+        public int Count { get; }
+
+        public Memory<T> this[int index] => throw new NotImplementedException();
+
+        public bool IsValid { get; internal set; }
+
+        class MemoryOwnerWrapper : MemoryManager<T>
+        {
+            private UniformMemoryGroupView<T> view;
+
+            private int index;
+
+            public MemoryOwnerWrapper(UniformMemoryGroupView<T> view, int index)
+            {
+                this.view = view;
+                this.index = index;
+            }
+
+            protected override void Dispose(bool disposing)
+            {
+            }
+
+            public override Span<T> GetSpan()
+            {
+                if (!this.view.IsValid)
+                {
+                    throw new InvalidOperationException();
+                }
+
+                return this.view[this.index].Span;
+            }
+
+            public override MemoryHandle Pin(int elementIndex = 0) => throw new NotImplementedException();
+
+            public override void Unpin() => throw new NotImplementedException();
+        }
+    }
+}

src/ImageSharp/Memory/DiscontinuousProto/UniformMemoryGroup{T}.Allocated.cs

@@ -0,0 +1,69 @@
+using System;
+using System.Buffers;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace SixLabors.ImageSharp.Memory.DiscontinuousProto
+{
+    public abstract partial class UniformMemoryGroup<T>
+    {
+        private class Allocated : UniformMemoryGroup<T>
+        {
+            private IMemoryOwner<T>[] memoryOwners;
+
+            public Allocated(IMemoryOwner<T>[] memoryOwners)
+            {
+                this.memoryOwners = memoryOwners;
+            }
+
+            public override IEnumerator<Memory<T>> GetEnumerator()
+            {
+                this.EnsureNotDisposed();
+                return this.memoryOwners.Select(mo => mo.Memory).GetEnumerator();
+            }
+
+
+            public override int Count
+            {
+                get
+                {
+                    this.EnsureNotDisposed();
+                    return this.memoryOwners.Length;
+                }
+            }
+
+            public override Memory<T> this[int index]
+            {
+                get
+                {
+                    this.EnsureNotDisposed();
+                    return this.memoryOwners[index].Memory;
+                }
+            }
+
+            public override void Dispose()
+            {
+                if (this.memoryOwners == null)
+                {
+                    return;
+                }
+
+                foreach (IMemoryOwner<T> memoryOwner in this.memoryOwners)
+                {
+                    memoryOwner.Dispose();
+                }
+
+                this.memoryOwners = null;
+                this.IsValid = false;
+            }
+
+            private void EnsureNotDisposed()
+            {
+                if (this.memoryOwners == null)
+                {
+                    throw new ObjectDisposedException(nameof(UniformMemoryGroup<T>));
+                }
+            }
+        }
+    }
+}

src/ImageSharp/Memory/DiscontinuousProto/UniformMemoryGroup{T}.External.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Collections.Generic;
+
+namespace SixLabors.ImageSharp.Memory.DiscontinuousProto
+{
+    public abstract partial class UniformMemoryGroup<T>
+    {
+        private class External : UniformMemoryGroup<T>
+        {
+            private readonly ReadOnlyMemory<Memory<T>> source;
+
+            public External(ReadOnlyMemory<Memory<T>> source)
+            {
+                // TODO: sizes should be uniform, validate!
+
+                this.source = source;
+            }
+
+            public override IEnumerator<Memory<T>> GetEnumerator()
+            {
+                for (int i = 0; i < this.source.Length; i++)
+                {
+                    yield return this.source.Span[i];
+                }
+            }
+
+            public override int Count => this.source.Length;
+
+            public override Memory<T> this[int index] => this.source.Span[index];
+
+            public override void Dispose()
+            {
+                // No ownership nothing to dispose
+            }
+        }
+    }
+}

src/ImageSharp/Memory/DiscontinuousProto/UniformMemoryGroup{T}.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+namespace SixLabors.ImageSharp.Memory.DiscontinuousProto
+{
+    /// <summary>
+    /// Represents a group of one or more uniformly-sized discontinuous memory segments, owned by this instance.
+    /// </summary>
+    /// <typeparam name="T">The element type.</typeparam>
+    public abstract partial class UniformMemoryGroup<T> : IUniformMemoryGroup<T>, IDisposable where T : struct
+    {
+        public abstract IEnumerator<Memory<T>> GetEnumerator();
+
+        IEnumerator IEnumerable.GetEnumerator() => this.GetEnumerator();
+
+        public abstract int Count { get; }
+
+        public abstract Memory<T> this[int index] { get; }
+
+        public abstract void Dispose();
+
+        public bool IsValid { get; protected set; }
+
+        public static UniformMemoryGroup<T> Allocate(MemoryAllocator allocator, long length)
+        {
+            long bufferCount = length / allocator.GetMaximumContiguousBufferLength();
+
+            // TODO: Allocate bufferCount buffers
+            throw new NotImplementedException();
+        }
+
+        public static UniformMemoryGroup<T> Wrap(params Memory<T>[] source) => Wrap(source.AsMemory());
+
+        public static UniformMemoryGroup<T> Wrap(ReadOnlyMemory<Memory<T>> source)
+        {
+            return new External(source);
+        }
+    }
+}

tests/ImageSharp.Tests/TestUtilities/TestMemoryAllocator.cs

@@ -24,6 +24,8 @@ namespace SixLabors.ImageSharp.Tests.Memory
 
         public IList<AllocationRequest> AllocationLog => this.allocationLog;
 
+        protected internal override int GetMaximumContiguousBufferLength() => int.MaxValue;
+
         public override IMemoryOwner<T> Allocate<T>(int length, AllocationOptions options = AllocationOptions.None)
         {
             T[] array = this.AllocateArray<T>(length, options);
@@ -152,4 +154,4 @@ namespace SixLabors.ImageSharp.Tests.Memory
             }
         }
     }
-}
+}