MemoryCache Evict Bug

[xboxeer]

Describe the bug

When we have a limit to the MemoryCache, its Evict logic does not behavior as expected This is a bug we found in community Why do I need to call twice the Set on my size limited MemoryCache when I hit the size limit?, the replier of this thread helped build a reproduce sample

To Reproduce

the below code can reproduce this issue

class Program
    {
        private static MemoryCache _cache;
        private static MemoryCacheEntryOptions _options;

        static void Main(string[] args)
        {
            _cache = new MemoryCache(new MemoryCacheOptions
            {
                SizeLimit = 2
            });

            _options = new MemoryCacheEntryOptions
            {
                Size = 1
            };
            _options.PostEvictionCallbacks.Add(new PostEvictionCallbackRegistration
            {
                EvictionCallback = (key, value, reason, state) =>
                {
                    if (reason == EvictionReason.Capacity)
                    {
                        Console.WriteLine($"Evicting '{key}' for capacity");
                    }
                }
            });

            Console.WriteLine(TestCache("first"));
            Console.WriteLine(TestCache("second"));
            Console.WriteLine(TestCache("third")); // starts compaction

            Thread.Sleep(1000);

            Console.WriteLine(TestCache("third"));
            Console.WriteLine(TestCache("third")); // now from cache
        }

        private static object TestCache(string id)
        {
            if (_cache.TryGetValue(id, out var cachedEntry))
            {
                return cachedEntry;
            }

            _cache.Set(id, $"{id} - cached", _options);
            return id;
        }
    }

Expected result should be

first
second
Evicting 'first' for capacity
third
third - cached

The actual result is

first
second
third
Evicting 'third' for capacity
Evicting 'first' for capacity
third
third - cached

Exceptions (if any)

Further technical details

• ASP.NET Core version 3.1
• Include the output of dotnet --info .NET Core SDK (reflecting any global.json): Version: 3.1.402 Commit: 9b5de826fd

Runtime Environment: OS Name: Windows OS Version: 10.0.19042 OS Platform: Windows RID: win10-x64 Base Path: C:\Program Files\dotnet\sdk\3.1.402\

Host (useful for support): Version: 3.1.8 Commit: 9c1330dedd

.NET Core SDKs installed: 2.1.202 [C:\Program Files\dotnet\sdk] 2.1.504 [C:\Program Files\dotnet\sdk] 2.1.505 [C:\Program Files\dotnet\sdk] 2.1.507 [C:\Program Files\dotnet\sdk] 2.1.508 [C:\Program Files\dotnet\sdk] 2.1.509 [C:\Program Files\dotnet\sdk] 2.1.511 [C:\Program Files\dotnet\sdk] 2.1.602 [C:\Program Files\dotnet\sdk] 2.1.700 [C:\Program Files\dotnet\sdk] 2.2.108 [C:\Program Files\dotnet\sdk] 2.2.300 [C:\Program Files\dotnet\sdk] 3.0.100 [C:\Program Files\dotnet\sdk] 3.1.402 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed: Microsoft.AspNetCore.All 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.All 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.All 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.All 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.All 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.All 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.All 2.1.22 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.All 2.2.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.All 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.App 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 2.1.22 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 2.2.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 3.0.1-dev [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 3.0.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.NETCore.App 1.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.1.22 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.2.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.WindowsDesktop.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

• The IDE (VS / VS Code/ VS4Mac) you're running on, and it's version VS 2019 16.7.3

[ghost]

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