From 12a3816c122f0d86968922480bd2e53f42bde365 Mon Sep 17 00:00:00 2001
From: Stephen Halter <halter73@gmail.com>
Date: Thu, 5 May 2016 15:00:58 -0700
Subject: [PATCH] Make some MemoryPoolBlock operations volatile

- Making MemoryPoolBlock.End volatile and using Volatile.Write for
  MemoryPoolBlock.Next prevents a race that could cause threads consuming
  blocks to skip produced bytes.
---
 src/Microsoft.AspNetCore.Server.Kestrel/Http/SocketInput.cs | 2 +-
 .../Infrastructure/MemoryPoolBlock.cs                       | 6 +++---
 .../Infrastructure/MemoryPoolIterator.cs                    | 5 +++--
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Server.Kestrel/Http/SocketInput.cs b/src/Microsoft.AspNetCore.Server.Kestrel/Http/SocketInput.cs
index 1588e83011..40532e17b4 100644
--- a/src/Microsoft.AspNetCore.Server.Kestrel/Http/SocketInput.cs
+++ b/src/Microsoft.AspNetCore.Server.Kestrel/Http/SocketInput.cs
@@ -105,7 +105,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
                     }
                     else
                     {
-                        _tail.Next = _pinned;
+                        Volatile.Write(ref _tail.Next, _pinned);
                         _tail = _pinned;
                     }
 
diff --git a/src/Microsoft.AspNetCore.Server.Kestrel/Infrastructure/MemoryPoolBlock.cs b/src/Microsoft.AspNetCore.Server.Kestrel/Infrastructure/MemoryPoolBlock.cs
index 25cab8c4f4..1bcd60ecaa 100644
--- a/src/Microsoft.AspNetCore.Server.Kestrel/Infrastructure/MemoryPoolBlock.cs
+++ b/src/Microsoft.AspNetCore.Server.Kestrel/Infrastructure/MemoryPoolBlock.cs
@@ -57,14 +57,14 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
         /// the Start is guaranteed to be equal to Array.Offset. The value of Start may be assigned anywhere between Data.Offset and
         /// Data.Offset + Data.Count, and must be equal to or less than End.
         /// </summary>
-        public int Start { get; set; }
+        public int Start;
 
         /// <summary>
         /// The End represents the offset into Array where the range of "active" bytes ends. At the point when the block is leased
         /// the End is guaranteed to be equal to Array.Offset. The value of Start may be assigned anywhere between Data.Offset and
         /// Data.Offset + Data.Count, and must be equal to or less than End.
         /// </summary>
-        public int End { get; set; }
+        public volatile int End;
 
         /// <summary>
         /// Reference to the next block of data when the overall "active" bytes spans multiple blocks. At the point when the block is
@@ -72,7 +72,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
         /// working memory. The "active" memory is grown when bytes are copied in, End is increased, and Next is assigned. The "active" 
         /// memory is shrunk when bytes are consumed, Start is increased, and blocks are returned to the pool.
         /// </summary>
-        public MemoryPoolBlock Next { get; set; }
+        public MemoryPoolBlock Next;
 
         ~MemoryPoolBlock()
         {
diff --git a/src/Microsoft.AspNetCore.Server.Kestrel/Infrastructure/MemoryPoolIterator.cs b/src/Microsoft.AspNetCore.Server.Kestrel/Infrastructure/MemoryPoolIterator.cs
index 8d65c5c377..202d15191f 100644
--- a/src/Microsoft.AspNetCore.Server.Kestrel/Infrastructure/MemoryPoolIterator.cs
+++ b/src/Microsoft.AspNetCore.Server.Kestrel/Infrastructure/MemoryPoolIterator.cs
@@ -4,6 +4,7 @@
 using System;
 using System.Diagnostics;
 using System.Numerics;
+using System.Threading;
 
 namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
 {
@@ -767,7 +768,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
                 {
                     var nextBlock = pool.Lease();
                     block.End = blockIndex;
-                    block.Next = nextBlock;
+                    Volatile.Write(ref block.Next, nextBlock);
                     block = nextBlock;
 
                     blockIndex = block.Data.Offset;
@@ -820,7 +821,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
                     {
                         var nextBlock = pool.Lease();
                         block.End = blockIndex;
-                        block.Next = nextBlock;
+                        Volatile.Write(ref block.Next, nextBlock);
                         block = nextBlock;
 
                         blockIndex = block.Data.Offset;