Runtime: Memory leak caused by use of ArrayPool<byte>.Shared in underlying libraries.

[bcuff]

Our application eventually runs out of memory after a few days of running. We've traced down the majority of heap usage to buffers allocated by the DefaultArrayPool.

We would like the ability to turn off or replace the ArrayPool.Shared implementation. Currently we're using a reflection hack to work around the issue.

Workaround:

    public class NullArrayPool<T> : ArrayPool<T>
    {
        public override T[] Rent(int minimumLength)
        {
            return new T[minimumLength];
        }

        public override void Return(T[] array, bool clearArray = false)
        {
        }
    }

    public static class ArrayPoolUtil
    {
        public static void SetShared<T>(ArrayPool<T> arrayPool)
        {
            var flags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static;
            var q = from field in typeof(ArrayPool<T>).GetTypeInfo().GetFields(flags)
                    where field.IsStatic && (field.Name == "s_sharedInstance" || field.Name == "<Shared>k__BackingField")
                    select field;
            var target = q.FirstOrDefault();
            if (target == null) throw new InvalidOperationException("Unable to set ArrayPool.Shared");
            target.SetValue(null, arrayPool);
        }
    }

    public static void Main()
    {
            ArrayPoolUtil.SetShared(new NullArrayPool<byte>()); // works around memory leak
            // ...
    }

[jkotas]

Yes, ArrayPool can keep a lot of unused memory alive.

I think a better fix would be to make GC aware of it and allow it to flush it.
https://github.com/dotnet/coreclr/issues/7747

[bcuff]

It would be great to have a better implementation that responded to memory pressure. I look forward to that happening.

That said... it would still be useful to swap out the implementation for the following reasons:

• Applications that don't want to trade memory for CPU
• Applications where the default implementation doesn't work well in some specific case

[stephentoub]

Closing as addressed by https://github.com/dotnet/coreclr/pull/17078.