EventListener does not project GCPerHeapHistory_V3 values array

[noahfalk]

The GCPerHeapHistory_V3 event has an array called 'Values'. This array of structs should be projected into the EventListener event model but it is absent. Most likely this is a broader issue handling array typed fields, or perhaps dynamically sized array-typed fields.

Repro:

using System;
using System.Collections.Generic;
using System.Diagnostics.Tracing;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp19
{
    class Program
    {
        static List<object> s_objects = new List<object>();

        static void Main(string[] args)
        {
            GCEventListener listener = new GCEventListener();
            Task.Run(AllocateMemory);
            Console.ReadLine();
        }

        static void AllocateMemory()
        {
            while (true)
            {
                s_objects.Add(new byte[50_000]);
                Thread.Sleep(10);
            }
        }
    }

    public class GCEventListener : EventListener
    {
        enum ClrRuntimeEventKeywords
        {
            GC = 0x1
        }

        protected override void OnEventSourceCreated(EventSource eventSource)
        {
            if (eventSource.Name.Equals("Microsoft-Windows-DotNETRuntime"))
            {
                EnableEvents(eventSource, EventLevel.Informational, (EventKeywords)ClrRuntimeEventKeywords.GC);
            }
        }
        protected override void OnEventWritten(EventWrittenEventArgs eventData)
        {
            if (eventData.EventName == "GCPerHeapHistory_V3")
            {
                Console.WriteLine(eventData.EventName);
                foreach (string name in eventData.PayloadNames)
                {
                    Console.WriteLine("    " + name);
                }
            }
        }
    }
}

Expected behavior: this app should print a payload field named "Values" in addition to the others
(and assuming that works you should be able to retrieve the array and access the nested fields)
Actual behavior: the app prints over payload fields, but not "Values"

[dionrhys]

This would be lovely to have so we could calculate before/peak size across the generations. It doesn't look like there are any other EventListener-based events that expose this.

I'm using your gist (https://gist.github.com/noahfalk/935e43bf69e3737f55164ac16f2d2ee6) as a workaround right now. I'm using EventPipe and the TraceEvent library so I can make use of its GCEnd event to get at TraceGC.HeapSizePeakMB and TraceGC.GenSizeBeforeMB[].

To be honest that works well and I can also get at TraceEventSource.Clr.GCAllocationTick for sampling allocations over time as well.

Is EventPipe the way to go here these days? I'm having a hard time figuring out whether EventListener or EventPipe (or something else) is the way to go for in-process GC monitoring.

[noahfalk]

Is EventPipe the way to go here these days? I'm having a hard time figuring out whether EventListener or EventPipe (or something else) is the way to go for in-process GC monitoring.

I think the tradeoffs right now are:
EventListener - doesn't depend on any extra libraries, has some limitations in what data is provided for each event (no stack trace, this issue above), no built-in analysis or abstractions on top of the raw events
EventPipe - requires the Microsoft.Diagnostics.NetCore.Client and TraceEvent NuGet packages use it easily, surfaces all the event data, TraceEvent includes some analysis and higher level abstractions if you want them

As long as you aren't worried about the extra dependencies (adds about ~3MB to the app) I'd suggest EventPipe.