The current answer is in the current spec for HostResolveImportedModule <https://www.ecma-international.org/ecma-262/#sec-hostresolveimportedmodule> :
> Each time this operation is called with a specific referencingScriptOrModule, specifier pair as arguments > it must return the same Module Record instance if it completes normally. In other words: The runtime generally cannot safely collect modules because all modules are "always" referenced by the thing that imported it. It gets more strict in HTML where all modules are globally referenced in the "module map". So even when it *looks* like a module isn't referenced by previous kinds of references (object properties etc.), there really isn't such a thing as an "unreferenced" module as long as the realm/context is alive. In short: There's no "module cache" in ES modules, it's an append-only module map. This also means that if you expect something to require GC, you maybe shouldn't be loading it as a module. E.g. JSON loaded via some future import mechanism would never be GC'd. In the fictional example of the huge MMORPG with many planets, you'd likely want to load the things you care about GC'ing via fetch() or some other mechanism that allows managing lifetime yourself.[1] Cheers, Jan On Wed, Jul 1, 2020 at 5:00 AM <[email protected]> wrote: > Send es-discuss mailing list submissions to > [email protected] > > To subscribe or unsubscribe via the World Wide Web, visit > https://mail.mozilla.org/listinfo/es-discuss > or, via email, send a message with subject or body 'help' to > [email protected] > > You can reach the person managing the list at > [email protected] > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of es-discuss digest..." > Today's Topics: > > 1. Re: Are ES Modules garbage collected? If so, do they > re-execute on next import? (Isiah Meadows) > > > > ---------- Forwarded message ---------- > From: Isiah Meadows <[email protected]> > To: Andrea Giammarchi <[email protected]> > Cc: Isiah Meadows <[email protected]>, Gus Caplan <[email protected]>, > es-discuss <[email protected]> > Bcc: > Date: Wed, 1 Jul 2020 00:47:30 -0700 > Subject: Re: Are ES Modules garbage collected? If so, do they re-execute > on next import? > That's part of the caching I'm referring to. And if the cache entry > for it has been evicted, I would *not* expect it to necessarily return > the same instance, consistent with the behavior with `require` and > `require.cache` in Node (and similar with most other module loaders > that support cache eviction). > > ----- > > Isiah Meadows > [email protected] > www.isiahmeadows.com > > On Tue, Jun 30, 2020 at 11:57 PM Andrea Giammarchi > <[email protected]> wrote: > > > > even if dereferenced, a dynamic import could re-reference it any time, > and I would expect it to still be the same module, it'd be a surprise > otherwise (cached things, same namespace checks, etc). > > > > On Wed, Jul 1, 2020 at 7:33 AM Isiah Meadows <[email protected]> > wrote: > >> > >> Just to expand on that, if the module record itself is dereferenced > >> (like if it's evicted from the cache somehow), then yes, it should be > >> collected as appropriate. However, I'm not aware of any major > >> implementation that offers that functionality. > >> > >> ----- > >> > >> Isiah Meadows > >> [email protected] > >> www.isiahmeadows.com > >> > >> On Tue, Jun 30, 2020 at 6:22 PM Gus Caplan <[email protected]> wrote: > >> > > >> > Modules in the spec are cached by specifier by modules that import > them. Modules in major implementations are additionally cached for the > entire realm by absolute URLs. I would say that for actual code (functions > and classes and whatnot) leaks aren't really a problem. Even if you import > a ton of levels, that's not that much memory. The main concern I've seen > raised is JSON modules, where once you import them the JSON object, which > can be quite large, will never be collected. Of course, there is a simple > solution to that (fetch) so it isn't a world ending problem. > >> > > >> > On Tue, Jun 30, 2020 at 7:41 PM #!/JoePea <[email protected]> wrote: > >> >> > >> >> I am curious: can modules be garbage collected if the exports are not > >> >> references by anything anymore? And if so, will the module be > >> >> re-evaluated the next time it is imported? > >> >> > >> >> I haven't tried an experiment to answer this yet. I'll be back to > post > >> >> findings if someone doesn't post an official answer first. > >> >> > >> >> I'm thinking about code longevity. For example, if we make > >> >> long-running web-based applications with many routes and features > (for > >> >> sake of example imagine a desktop environment, or a MMORPG game, with > >> >> apps or components that are loaded within the same context). Over > >> >> time, if imports are not collected, then it means we have a memory > >> >> leak. > >> >> > >> >> Imagine, for example, an infinite-universe MMORPG where you can land > >> >> on different planets where the code for features of a planet are > >> >> provided by third parties as ES Modules. I know, this might not be a > >> >> safe idea to import any code into an app, but just imagine it for > sake > >> >> of example (imagine we have a continuous integration system to test > >> >> and verify code security, or something, before that code is allowed > to > >> >> be consumed in the app). Imagine you play this app for many many > days, > >> >> and visit many places, and you leave the app running the whole time > >> >> (because farming for resources is disabled if the app is not running, > >> >> or something). > >> >> > >> >> I would imagine that we want unused modules (when we leave a planet, > >> >> for example) to be (destroyed) garbage collected so that we don't > >> >> waste memory. > >> >> > >> >> #!/JoePea > >> >> _______________________________________________ > >> >> es-discuss mailing list > >> >> [email protected] > >> >> https://mail.mozilla.org/listinfo/es-discuss > >> > > >> > _______________________________________________ > >> > es-discuss mailing list > >> > [email protected] > >> > https://mail.mozilla.org/listinfo/es-discuss > >> _______________________________________________ > >> es-discuss mailing list > >> [email protected] > >> https://mail.mozilla.org/listinfo/es-discuss > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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