Blazor WASM + looping JsonSerializer.Serialize() results in out-of memory

[JeremyKnaggs]

Describe the bug

I was doing some stress testing and found memory doesn't seem to be released inside a loop running in Blazor WASM apps. If I run the below method, I can watch the browser's memory continue to increase until the app crashes.

To Reproduce

@code {

private void StressMemory()
{

    Dictionary<string, double[]> LotsOfData = new Dictionary<string, double[]>();

    int arraySize = 1000000;
    var ary = new double[arraySize];
    Random r = new Random();

    for (int i = 0; i < 1000; i++)
    {

        Console.WriteLine(i.ToString() + " Starting");
        string key = "key";
        if (!LotsOfData.ContainsKey(key)) LotsOfData.Add(key, ary);
        for (int j = 0; j < arraySize; j++)
        {
            LotsOfData[key][j] = r.NextDouble();
        }
        Console.WriteLine("Serializing: "+i.ToString());

        JsonSerializer.Serialize(LotsOfData);
        Console.WriteLine(i.ToString() + " Done");
    }

}

}

Exceptions (if any)

Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100]
Unhandled exception rendering component: Out of memory
System.OutOfMemoryException: Out of memory
at System.Buffers.TlsOverPerCoreLockedStacksArrayPool1[T].Rent (System.Int32 minimumLength) <0x1a8fcd0 + 0x0014c> in <filename unknown>:0 at System.Text.Json.PooledByteBufferWriter.CheckAndResizeBuffer (System.Int32 sizeHint) <0x1eafe40 + 0x00074> in <filename unknown>:0 at System.Text.Json.PooledByteBufferWriter.GetMemory (System.Int32 sizeHint) <0x1eafd68 + 0x00006> in <filename unknown>:0 at System.Text.Json.Utf8JsonWriter.Grow (System.Int32 requiredSize) <0x1ebc810 + 0x000b6> in <filename unknown>:0 at System.Text.Json.Utf8JsonWriter.WriteNumberValueMinimized (System.Double value) <0x29af080 + 0x0002e> in <filename unknown>:0 at System.Text.Json.Utf8JsonWriter.WriteNumberValue (System.Double value) <0x29aee60 + 0x0003e> in <filename unknown>:0 at System.Text.Json.Serialization.Converters.JsonConverterDouble.Write (System.Text.Json.Utf8JsonWriter writer, System.Double value, System.Text.Json.JsonSerializerOptions options) <0x29aeca0 + 0x0000c> in <filename unknown>:0 at System.Text.Json.JsonPropertyInfoNotNullable4[TClass,TDeclaredProperty,TRuntimeProperty,TConverter].OnWriteEnumerable (System.Text.Json.WriteStackFrame& current, System.Text.Json.Utf8JsonWriter writer) <0x29aeab8 + 0x00088> in :0
at System.Text.Json.JsonPropertyInfo.WriteEnumerable (System.Text.Json.WriteStack& state, System.Text.Json.Utf8JsonWriter writer) <0x1eb0e98 + 0x0001e> in :0
at System.Text.Json.JsonSerializer.HandleEnumerable (System.Text.Json.JsonClassInfo elementClassInfo, System.Text.Json.JsonSerializerOptions options, System.Text.Json.Utf8JsonWriter writer, System.Text.Json.WriteStack& state) <0x1ebb578 + 0x00158> in :0
at System.Text.Json.JsonSerializer.Write (System.Text.Json.Utf8JsonWriter writer, System.Int32 originalWriterDepth, System.Int32 flushThreshold, System.Text.Json.JsonSerializerOptions options, System.Text.Json.WriteStack& state) <0x1eab1f0 + 0x0007a> in :0
at System.Text.Json.JsonSerializer.WriteCore (System.Text.Json.Utf8JsonWriter writer, System.Object value, System.Type type, System.Text.Json.JsonSerializerOptions options) <0x1c887a8 + 0x0008a> in :0
at System.Text.Json.JsonSerializer.WriteCore (System.Text.Json.PooledByteBufferWriter output, System.Object value, System.Type type, System.Text.Json.JsonSerializerOptions options) <0x1c87ef0 + 0x00040> in :0
at System.Text.Json.JsonSerializer.WriteCoreString (System.Object value, System.Type type, System.Text.Json.JsonSerializerOptions options) <0x1c87af8 + 0x0003c> in :0
at System.Text.Json.JsonSerializer.Serialize[TValue] (TValue value, System.Text.Json.JsonSerializerOptions options) <0x299f310 + 0x0000c> in :0
at TestBlazorMemoryRelease.MemoryCheck.MemoryCheck.StressMemory () <0x21e6ac8 + 0x000e8> in :0
at TestBlazorMemoryRelease.Pages.Counter.StressMemory () <0x21e64b0 + 0x0000a> in :0
at Microsoft.AspNetCore.Components.EventCallbackWorkItem.InvokeAsync[T] (System.MulticastDelegate delegate, T arg) <0x20cf748 + 0x0005e> in :0
at Microsoft.AspNetCore.Components.EventCallbackWorkItem.InvokeAsync (System.Object arg) <0x20c95a0 + 0x0000a> in :0
at Microsoft.AspNetCore.Components.ComponentBase.Microsoft.AspNetCore.Components.IHandleEvent.HandleEventAsync (Microsoft.AspNetCore.Components.EventCallbackWorkItem callback, System.Object arg) <0x20c9508 + 0x0000a> in :0
at Microsoft.AspNetCore.Components.EventCallback.InvokeAsync (System.Object arg) <0x20c90d0 + 0x00040> in :0
at Microsoft.AspNetCore.Components.RenderTree.Renderer.DispatchEventAsync (System.UInt64 eventHandlerId, Microsoft.AspNetCore.Components.RenderTree.EventFieldInfo fieldInfo, System.EventArgs eventArgs) <0x20c86c0 + 0x000a8> in :0
f.printErr @ blazor.webassembly.js:1

Further technical details

• ASP.NET Core version
• Include the output of dotnet --info

[JeremyKnaggs]

I realized this is more related to mono: mono/mono#19665

[JeremyKnaggs]

Also: mono/mono#20009