From 854ea5d0962921a8f1831376f77b1bef8a57b75a Mon Sep 17 00:00:00 2001
From: Anton Firszov <antonfir@gmail.com>
Date: Mon, 21 Feb 2022 23:25:22 +0100
Subject: [PATCH] workaround for #2001 / 
 https://github.com/dotnet/runtime/issues/65466

---
 .../UniformUnmanagedMemoryPoolMemoryAllocator.cs    | 13 +++++++++++--
 .../UniformUnmanagedPoolMemoryAllocatorTests.cs     | 13 +++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/ImageSharp/Memory/Allocators/UniformUnmanagedMemoryPoolMemoryAllocator.cs b/src/ImageSharp/Memory/Allocators/UniformUnmanagedMemoryPoolMemoryAllocator.cs
index 16a3cb73d1..5f591a9bb3 100644
--- a/src/ImageSharp/Memory/Allocators/UniformUnmanagedMemoryPoolMemoryAllocator.cs
+++ b/src/ImageSharp/Memory/Allocators/UniformUnmanagedMemoryPoolMemoryAllocator.cs
@@ -74,6 +74,10 @@ namespace SixLabors.ImageSharp.Memory
             this.nonPoolAllocator = new UnmanagedMemoryAllocator(unmanagedBufferSizeInBytes);
         }
 
+        // This delegate allows overriding the method returning the available system memory,
+        // so we can test our workaround for https://github.com/dotnet/runtime/issues/65466
+        internal static Func<long> GetTotalAvailableMemoryBytes { get; set; } = () => GC.GetGCMemoryInfo().TotalAvailableMemoryBytes;
+
         /// <inheritdoc />
         protected internal override int GetBufferCapacityInBytes() => this.poolBufferSizeInBytes;
 
@@ -152,8 +156,13 @@ namespace SixLabors.ImageSharp.Memory
             // https://github.com/dotnet/runtime/issues/55126#issuecomment-876779327
             if (Environment.Is64BitProcess || !RuntimeInformation.FrameworkDescription.StartsWith(".NET 5.0"))
             {
-                GCMemoryInfo info = GC.GetGCMemoryInfo();
-                return info.TotalAvailableMemoryBytes / 8;
+                long total = GetTotalAvailableMemoryBytes();
+
+                // Workaround for https://github.com/dotnet/runtime/issues/65466
+                if (total > 0)
+                {
+                    return total / 8;
+                }
             }
 #endif
 
diff --git a/tests/ImageSharp.Tests/Memory/Allocators/UniformUnmanagedPoolMemoryAllocatorTests.cs b/tests/ImageSharp.Tests/Memory/Allocators/UniformUnmanagedPoolMemoryAllocatorTests.cs
index 45a7cc278e..0c59e334c5 100644
--- a/tests/ImageSharp.Tests/Memory/Allocators/UniformUnmanagedPoolMemoryAllocatorTests.cs
+++ b/tests/ImageSharp.Tests/Memory/Allocators/UniformUnmanagedPoolMemoryAllocatorTests.cs
@@ -379,5 +379,18 @@ namespace SixLabors.ImageSharp.Tests.Memory.Allocators
                 g1.GetSpan()[0] = 42;
             }
         }
+
+        [Fact]
+        public void Issue2001_NegativeMemoryReportedByGc()
+        {
+            RemoteExecutor.Invoke(RunTest).Dispose();
+
+            static void RunTest()
+            {
+                // Emulate GC.GetGCMemoryInfo() issue https://github.com/dotnet/runtime/issues/65466
+                UniformUnmanagedMemoryPoolMemoryAllocator.GetTotalAvailableMemoryBytes = () => -402354176;
+                _ = MemoryAllocator.Create();
+            }
+        }
     }
 }