From 5b0ce2dd4038d8978f9be6baff38b7ef70caaff8 Mon Sep 17 00:00:00 2001
From: Ben <benmwatson@users.noreply.github.com>
Date: Thu, 22 Jul 2021 14:14:07 -0700
Subject: [PATCH] Fix overflow error in ReturnBlocks (#187)

* Fix overflow error in ReturnBlocks

* Check for underflow/overflow in debug builds

Co-authored-by: Ben Watson <bewatson@microsoft.com>
---
 UnitTests/Tests.cs                            | 29 +++++++++++++++++++
 UnitTests/UnitTests.csproj                    |  1 +
 ...Microsoft.IO.RecyclableMemoryStream.csproj |  1 +
 src/RecyclableMemoryStreamManager.cs          |  2 +-
 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/UnitTests/Tests.cs b/UnitTests/Tests.cs
index a6729cf1..64dd1092 100644
--- a/UnitTests/Tests.cs
+++ b/UnitTests/Tests.cs
@@ -3384,6 +3384,35 @@ private RecyclableMemoryStream GetRandomStream()
         }
         #endregion
 
+        #region Bug Reports
+        // Issue #176 - SmallPoolInUseSize, SmallPoolFreeSize
+        [Test]
+        public void Issue176_PoolInUseSizeDoesNotDecrease()
+        {
+            long maximumFreeSmallPoolBytes = 32000L * 128000; //4096000000
+            long maximumFreeLargePoolBytes = UInt32.MaxValue;
+            int blockSize = 128000;
+
+            var mgr = new RecyclableMemoryStreamManager(blockSize, 1<<20, 8 * (1<<20),
+                                              maximumFreeSmallPoolBytes, maximumFreeLargePoolBytes);
+
+            MemoryStream fillStream = mgr.GetStream("pool", requiredSize: 128000, asContiguousBuffer: true);
+            byte[] block1 = new byte[128000];
+            long test1 = 4096000000;
+            int test2 = 128000;
+            for (int i = 0; i < 32000; i++)
+            {
+                fillStream.Write(block1, 0, 128000);
+                test1 -= test2;
+            }
+
+            Assert.That(test1, Is.EqualTo(0));
+            Assert.That(mgr.SmallPoolInUseSize, Is.EqualTo(maximumFreeSmallPoolBytes));
+            fillStream.Dispose();
+            Assert.That(mgr.SmallPoolInUseSize, Is.EqualTo(0));
+        }
+        #endregion
+
         protected abstract bool AggressiveBufferRelease { get; }
 
         protected virtual bool UseExponentialLargeBuffer
diff --git a/UnitTests/UnitTests.csproj b/UnitTests/UnitTests.csproj
index ec11a7ff..548f8d9d 100644
--- a/UnitTests/UnitTests.csproj
+++ b/UnitTests/UnitTests.csproj
@@ -3,6 +3,7 @@
     <AssemblyName>Microsoft.IO.RecyclableMemoryStream.UnitTests</AssemblyName>
     <TargetFramework>net5.0</TargetFramework>
     <DebugType>Full</DebugType> <!-- NUnit in VS2017 needs this instead of the new slimmer PDBs -->
+    <CheckForOverflowUnderflow>true</CheckForOverflowUnderflow>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="nunit" Version="3.13.2" />
diff --git a/src/Microsoft.IO.RecyclableMemoryStream.csproj b/src/Microsoft.IO.RecyclableMemoryStream.csproj
index 53f9a450..bdc5111d 100644
--- a/src/Microsoft.IO.RecyclableMemoryStream.csproj
+++ b/src/Microsoft.IO.RecyclableMemoryStream.csproj
@@ -21,6 +21,7 @@
     <PackageProjectUrl>https://github.com/Microsoft/Microsoft.IO.RecyclableMemoryStream</PackageProjectUrl>
     <IncludeBuildOutput>true</IncludeBuildOutput>
     <LangVersion>9.0</LangVersion>
+    <CheckForOverflowUnderflow Condition="'$(Configuration)' == 'Debug'">true</CheckForOverflowUnderflow>
   </PropertyGroup>
   <!-- for assembly signing we use a magic variable coupled with a special build definition which skips UTs -->
   <PropertyGroup Condition="'$(SignedBuild)' == 'true'">
diff --git a/src/RecyclableMemoryStreamManager.cs b/src/RecyclableMemoryStreamManager.cs
index 219bc137..f3725846 100644
--- a/src/RecyclableMemoryStreamManager.cs
+++ b/src/RecyclableMemoryStreamManager.cs
@@ -562,7 +562,7 @@ internal void ReturnBlocks(ICollection<byte[]> blocks, Guid id, string tag)
                 throw new ArgumentNullException(nameof(blocks));
             }
 
-            var bytesToReturn = blocks.Count * this.BlockSize;
+            long bytesToReturn = (long)blocks.Count * (long)this.BlockSize;
             Interlocked.Add(ref this.smallPoolInUseSize, -bytesToReturn);
 
             foreach (var block in blocks)