Use graduated buffers

Author: JimBobSquarePants

src/ImageSharp/IO/ChunkedMemoryStream.cs

@@ -16,39 +16,17 @@ namespace SixLabors.ImageSharp.IO
     /// </summary>
     internal sealed class ChunkedMemoryStream : Stream
     {
-        /// <summary>
-        /// The default length in bytes of each buffer chunk when allocating large buffers.
-        /// </summary>
-        public const int DefaultLargeChunkSize = 1024 * 1024 * 4; // 4 Mb
-
-        /// <summary>
-        /// The threshold at which to switch to using the large buffer.
-        /// </summary>
-        public const int DefaultLargeChunkThreshold = DefaultLargeChunkSize / 4; // 1 Mb
-
-        /// <summary>
-        /// The default length in bytes of each buffer chunk when allocating small buffers.
-        /// </summary>
-        public const int DefaultSmallChunkSize = DefaultLargeChunkSize / 32; // 128 Kb
-
         // The memory allocator.
         private readonly MemoryAllocator allocator;
 
         // Data
         private MemoryChunk memoryChunk;
 
-        // The length, in bytes, of each large buffer chunk
-        private readonly int largeChunkSize;
-
-        // The length, in bytes of the total allocation threshold that triggers switching from
-        // small to large buffer chunks.
-        private readonly int largeChunkThreshold;
-
-        // The current length, in bytes, of each buffer chunk
-        private int chunkSize;
+        // The total number of allocated chunks
+        private int chunkCount;
 
-        // The total allocation length, in bytes
-        private int totalAllocation;
+        // The length of the largest contiguous buffer that can be handled by the allocator.
+        private readonly int allocatorCapacity;
 
         // Has the stream been disposed.
         private bool isDisposed;
@@ -72,12 +50,7 @@ public ChunkedMemoryStream(MemoryAllocator allocator)
         {
             Guard.NotNull(allocator, nameof(allocator));
 
-            // Tweak our buffer sizes to take the minimum of the provided buffer sizes
-            // or values scaled from the allocator buffer capacity which provides us with the largest
-            // available contiguous buffer size.
-            this.largeChunkSize = Math.Min(DefaultLargeChunkSize, allocator.GetBufferCapacityInBytes());
-            this.largeChunkThreshold = Math.Min(DefaultLargeChunkThreshold, this.largeChunkSize / 4);
-            this.chunkSize = Math.Min(DefaultSmallChunkSize, this.largeChunkSize / 32);
+            this.allocatorCapacity = allocator.GetBufferCapacityInBytes();
             this.allocator = allocator;
         }
 
@@ -236,7 +209,7 @@ protected override void Dispose(bool disposing)
                 this.memoryChunk = null;
                 this.writeChunk = null;
                 this.readChunk = null;
-                this.totalAllocation = 0;
+                this.chunkCount = 0;
             }
             finally
             {
@@ -548,13 +521,10 @@ private void EnsureNotDisposed()
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private MemoryChunk AllocateMemoryChunk()
         {
-            if (this.totalAllocation >= this.largeChunkThreshold)
-            {
-                this.chunkSize = this.largeChunkSize;
-            }
-
-            IMemoryOwner<byte> buffer = this.allocator.Allocate<byte>(this.chunkSize);
-            this.totalAllocation += this.chunkSize;
+            // Tweak our buffer sizes to take the minimum of the provided buffer sizes
+            // or the allocator buffer capacity which provides us with the largest
+            // available contiguous buffer size.
+            IMemoryOwner<byte> buffer = this.allocator.Allocate<byte>(Math.Min(this.allocatorCapacity, GetChunkSize(this.chunkCount++)));
 
             return new MemoryChunk
             {
@@ -573,6 +543,16 @@ private void ReleaseMemoryChunks(MemoryChunk chunk)
             }
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static int GetChunkSize(int i)
+        {
+#pragma warning disable IDE1006 // Naming Styles
+            const int _128K = 1 << 17;
+            const int _4M = 1 << 22;
+            return i < 16 ? _128K * (1 << (i / 4)) : _4M;
+#pragma warning restore IDE1006 // Naming Styles
+        }
+
         private sealed class MemoryChunk : IDisposable
         {
             private bool isDisposed;

tests/ImageSharp.Tests/IO/ChunkedMemoryStreamTests.cs

@@ -18,6 +18,16 @@ namespace SixLabors.ImageSharp.Tests.IO
     /// </summary>
     public class ChunkedMemoryStreamTests
     {
+        /// <summary>
+        /// The default length in bytes of each buffer chunk when allocating large buffers.
+        /// </summary>
+        private const int DefaultLargeChunkSize = 1024 * 1024 * 4; // 4 Mb
+
+        /// <summary>
+        /// The default length in bytes of each buffer chunk when allocating small buffers.
+        /// </summary>
+        private const int DefaultSmallChunkSize = DefaultLargeChunkSize / 32; // 128 Kb
+
         private readonly MemoryAllocator allocator;
 
         public ChunkedMemoryStreamTests() => this.allocator = Configuration.Default.MemoryAllocator;
@@ -51,11 +61,11 @@ public void MemoryStream_ReadTest_Negative()
         }
 
         [Theory]
-        [InlineData(ChunkedMemoryStream.DefaultSmallChunkSize)]
-        [InlineData((int)(ChunkedMemoryStream.DefaultSmallChunkSize * 1.5))]
-        [InlineData(ChunkedMemoryStream.DefaultSmallChunkSize * 4)]
-        [InlineData((int)(ChunkedMemoryStream.DefaultSmallChunkSize * 5.5))]
-        [InlineData(ChunkedMemoryStream.DefaultSmallChunkSize * 16)]
+        [InlineData(DefaultSmallChunkSize)]
+        [InlineData((int)(DefaultSmallChunkSize * 1.5))]
+        [InlineData(DefaultSmallChunkSize * 4)]
+        [InlineData((int)(DefaultSmallChunkSize * 5.5))]
+        [InlineData(DefaultSmallChunkSize * 16)]
         public void MemoryStream_ReadByteTest(int length)
         {
             using MemoryStream ms = this.CreateTestStream(length);
@@ -72,11 +82,11 @@ public void MemoryStream_ReadByteTest(int length)
         }
 
         [Theory]
-        [InlineData(ChunkedMemoryStream.DefaultSmallChunkSize)]
-        [InlineData((int)(ChunkedMemoryStream.DefaultSmallChunkSize * 1.5))]
-        [InlineData(ChunkedMemoryStream.DefaultSmallChunkSize * 4)]
-        [InlineData((int)(ChunkedMemoryStream.DefaultSmallChunkSize * 5.5))]
-        [InlineData(ChunkedMemoryStream.DefaultSmallChunkSize * 16)]
+        [InlineData(DefaultSmallChunkSize)]
+        [InlineData((int)(DefaultSmallChunkSize * 1.5))]
+        [InlineData(DefaultSmallChunkSize * 4)]
+        [InlineData((int)(DefaultSmallChunkSize * 5.5))]
+        [InlineData(DefaultSmallChunkSize * 16)]
         public void MemoryStream_ReadByteBufferTest(int length)
         {
             using MemoryStream ms = this.CreateTestStream(length);
@@ -95,11 +105,11 @@ public void MemoryStream_ReadByteBufferTest(int length)
         }
 
         [Theory]
-        [InlineData(ChunkedMemoryStream.DefaultSmallChunkSize)]
-        [InlineData((int)(ChunkedMemoryStream.DefaultSmallChunkSize * 1.5))]
-        [InlineData(ChunkedMemoryStream.DefaultSmallChunkSize * 4)]
-        [InlineData((int)(ChunkedMemoryStream.DefaultSmallChunkSize * 5.5))]
-        [InlineData(ChunkedMemoryStream.DefaultSmallChunkSize * 16)]
+        [InlineData(DefaultSmallChunkSize)]
+        [InlineData((int)(DefaultSmallChunkSize * 1.5))]
+        [InlineData(DefaultSmallChunkSize * 4)]
+        [InlineData((int)(DefaultSmallChunkSize * 5.5))]
+        [InlineData(DefaultSmallChunkSize * 16)]
         public void MemoryStream_ReadByteBufferSpanTest(int length)
         {
             using MemoryStream ms = this.CreateTestStream(length);