[JSC] Prune about-to-be-notified rejected promises list at GC flip

• Component: JavaScriptCore
• Status: NEW ---

[Ross Kirsling]

From bug 197172 comment 36:

> If you have a loop with:
> 
> let p = new Promise((resolve, reject) => {
>     ...
>     reject(p)
> });
>
> p will be kept alive until the the microtasks are drained. Which means programs will OOM if they never drain all their microtasks...
>
> I think, at least, you'll need to clear handled promises at the GC flip. See where we call finalizeUnconditionalFinalizers.

Given the WHATWG spec*, I don't believe this is something we can address for the normal, web-hosted case (i.e. the "unhandledrejection" event), but it would be a possible improvement for rejection tracking in a standalone JSContext (which has no spec).

[*] https://html.spec.whatwg.org/multipage/webappapis.html#unhandled-promise-rejections