ClearScript 7.5

[andersekdahl]

Hi!
We've been using ClearScript for something like 10 years now, and we're forever grateful to this library and what it helped us do in .NET!

We upgraded to ClearScript 7.5 a couple of months ago and I recently came across quite a lot of AccessViolationExceptions that crashed our application. It went mostly unnoticed as we have 5 instances behind a load balancer. We've had about a handful of crashes per day this week and we've most likely had that since we upgraded. We looked at different crash dumps but couldn't find anything that pointed at this being our fault. So today we tried downgrading ClearScript to 7.4 and not only did the crashes disappear, our response times got almost cut in half.

I'm not sure how much of this is actionable, but I wanted to bring it up. We'd be happy to help to try to pin point the issues. We still have a couple of crash dumps that we can share in private if that would be helpful. We can also share more details about we're using ClearScript of course.

[ClearScriptLib]

Hi @andersekdahl,

Thanks for your kind words, and sorry about the issues you're encountering. We'll be happy to take a look at a crash dump if you can share one.

Thanks!

[andersekdahl]

I spoke too soon about the performance regression, even though the ClearScript change was the only thing we deployed it seems we had a spike of fast requests after deploy that made the average look like everything suddenly got faster. When digging deeper I see no change in the time it takes for the ClearScript calls we make between 7.4 and 7.5.

Do you have an email I can send a link with the crash dumps to?

[ClearScriptLib]

Hi @andersekdahl,

Do you have an email I can send a link with the crash dumps to?

Yes. Please send it to clearscript@clearfoundry.net.

Thanks!

[andersekdahl]

I've sent you an email now!

[ClearScriptLib]

Hi @andersekdahl,

Thanks for sharing your crash dumps. We've taken a look, and all of them indicate null pointer access deep within V8's handling of ephemerons – a concept V8 uses internally to implement JavaScript APIs such as WeakRef, WeakSet, WeakMap, and FinalizationRegistry. Does your application use any of them?

In any case, the V8 version that ClearScript 7.5 uses is now over a year old, which is ancient by V8 standards, and ephemeron handling – and GC in general – is one of the most frequently patched and rapidly evolving areas of V8. With issues like this, the rule is "upgrade first, investigate later", and, unfortunately, ClearScript 7.5 is still our latest release.

Historically, we've issued releases much more frequently, but things have slowed down recently. ClearScript is a side project, and we simply haven't had much time. Nevertheless, this is the sort of issue that we prioritize over new features, so we'll try to get a new release out ASAP, paired with the latest stable V8 release.

In the meantime, we'd love to know more about how your application uses ClearScript. For example, does it spin up new V8ScriptEngine instances frequently? Are those instances long-lived? Does your application only run trusted scripts? Any information could be helpful.

Thank you!

[andersekdahl]

I can't see any references to any of the weak APIs in our code, but there might be uses of them in npm packages we use which gets executed in ClearScript. I'll take a look tomorrow.

We're creating V8ScriptEngine instances at startup, one instance per core which I think is 16. Then we reuse those instances during the whole lifetime of our application. Then we periodically run GC on the instances after they've served X number of requests.

I really appreciate you looking into this and prioritizing it, but do know that there's no real stress from us at least. We're just happy that this library exist and has worked so well for us!