Extensive garbage collection when using an event with a connection from script

[DoctorGester]

Hi,

We have a game server instance running in JS which is managed from C# code.

Knowing how expensive interop between C# and JS is, I have reduced the interaction scope to a minimum, however I can't figure out if it's possible to reduce the GC pressure and amount of allocations produced by C# code when invoking an event handler.

Specifically, the code looks something like this:

public delegate void OnGameTick(double time);

    public event OnGameTick? Tick;

    public void Start() {
        gameScript.Start();

        var remainingTimeLimitMs = 0L;
        var time = Stopwatch.StartNew();

        while (true) {
            var tickTimeMs = 33L;

            while (remainingTimeLimitMs >= tickTimeMs) {
                Tick?.Invoke(gameTime);
                gameTime += (tickTimeMs / 1000d);
                remainingTimeLimitMs -= tickTimeMs;
            }

            Thread.Sleep((int) tickTimeMs);

            remainingTimeLimitMs += time.ElapsedMilliseconds;
            time.Restart();
        }
    }

And the script trivially connects to the Tick handler with

    GameScript.Tick.connect(time => {
        GameRules.SetGameTime(time);
        update();
    });

Now, the call to Tick?.Invoke(gameTime) produces an intense number of allocations in the Small Object Heap, multiple gigabytes per minute. Is there a way to invoke script functions and pass data in a more garbage collector friendly way?

[ClearScriptLib]

Hi @DoctorGester,

Now, the call to Tick?.Invoke(gameTime) produces an intense number of allocations in the Small Object Heap, multiple gigabytes per minute.

Hmm, can you tell what all those objects are? Also, do you know approximately how many events your application fires per minute?

Thanks!

[DoctorGester]

That's right, but your inner loop above (the one that fires the event) doesn't use timing primitives. On the other hand, if that inner while isn't expected to loop many times per outer while, then moving it into the script engine isn't likely to be a big win.

Yes the inner loop is not expected to be fired many times, it maybe expected to loop twice at most.

ClearScript could provide a synchronous delay implemented entirely in unmanaged code

That would actually be great.

What other host services would you need to invoke with similar frequency?

Not sure I understood the question here, what is meant by host services here?

[ClearScriptLib]

ClearScript could provide a synchronous delay implemented entirely in unmanaged code

That would actually be great.

Great! Would a simple sleep(milliseconds) be sufficient?

What other host services would you need to invoke with similar frequency?

Not sure I understood the question here, what is meant by host services here?

Sorry, "host services" simply refers to facilities not covered by the JavaScript environment and not amenable to a pure JavaScript implementation. A sleep function is one example. We were wondering if there's anything else we could provide that would enable you to move your outer loop into the script engine.

[DoctorGester]

Great! Would a simple sleep(milliseconds) be sufficient?

Yes!

Sorry, "host services" simply refers to facilities not covered by the JavaScript environment and not amenable to a pure JavaScript implementation

Oh I see, sure. I would also need some way to actually measure time more or less accurately, such as performance.now() in browsers/nodejs. I'm currently using a C# implementation of that, but that itself can incur serious overhead, so I'm not sure if it would work for ms-precision measurements.

[ClearScriptLib]

Hi @DoctorGester,

Great! Would a simple sleep(milliseconds) be sufficient?

Yes!

We've looked at this and found that the even the best OS sleep primitives are a bit unpredictable, at least on Windows, so the function we're adding looks like this:

Performance.sleep(delay, precise);

If precise is false or unspecified, sleep uses an OS sleep primitive. If precise is true, it performs a "cooperative spin wait", which provides excellent precision at the cost of mild CPU load (≤3% in our tests).

Additionally, we're adding a way to increase native timer resolution, enhancing the precision of the OS sleep primitive. It's only effective on Windows, but Linux and macOS don't seem to need it anyway.

The Performance object will also provide a now method and a timeOrigin property that mirror similar Web and Node.js APIs. Hopefully that'll cover your timing needs. If not, please let us know!

Cheers!

[DoctorGester]

Great, that sounds like exactly what we need!

[ClearScriptLib]

Version 7.4.5 added AddPerformanceObject and SetTimerResolution to V8ScriptEngineFlags.