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This still doesn't fix the biggest issue with running non-javascript code in the browser: browsers still offer no way to know when a value is collected. e.g. i

This still doesn't fix the biggest issue with running non-javascript code in the browser: browsers still offer no way to know when a value is collected. e.g. if I allocate a callback function, and hand it to setTimeout, I have no way to know when to collect it. Sure, you can encode rules about some of the common functions; but as soon as you get to e.g. attaching an 'onreadystatechange' to an XHR: you can't follow all the different code paths. Every time a proposal comes up to fix this: - GC callbacks - Weak valued maps - Proxy with collection trap The proposal gets squashed. Unless this is attended to Javascript remains the required language on the web.

BrendanEich 11y ago
Read up, you've missed a memo :-P. Plan for Harmony-era weak refs is to notify in next event loop turn. Note turn-based notification. No way will exact GC schedule be leaked via callbacks from the GC. Ditto anything like Java's post-mortem finalization. But your "e.g." is unclear, though. Why do you need to manually deallocate a callback function passed to setTimeout?
- daurnimator 11y ago
  > Read up, you've missed a memo :-P. Plan for Harmony-era weak refs is to notify in next event loop turn. Got a link to the memo? I haven't heard about this one. > Why do you need to manually deallocate a callback function passed to setTimeout? One of my use cases is running lua in the browser. see lua.vm.js: https://kripken.github.io/lua.vm.js/repl.html https://kripken.github.io/lua.vm.js/repl.html When you pass a lua function to a javascript function, I create a 'proxy' object that holds a reference to the function in the lua VM. Only if javascript tells me it's "done" with it can I drop the ref inside the lua VM.
  - chadaustin 11y ago
    FWIW, this is exactly the same problem we had with making it possible for Embind to allow passing C++ functions into setTimeout. We'd need to synthesize a JavaScript function that holds a wrapper object for the C++ function, and that wrapper object would need to be deallocated when the timer is done. For general callbacks, this is a hard problem, and finalizers would provide a clean way to solve it.
  - BrendanEich 11y ago
    See, e.g., https://esdiscuss.org/topic/weak-event-listener#content-2 https://esdiscuss.org/topic/weak-event-listener#content-2 It's hard to find something fresh. I will stir the pot at the July TC39 meeting and get the committee on the record for weak refs with turn-delayed notification, or bust!
    - daurnimator 11y ago
      > See, e.g., > https://esdiscuss.org/topic/weak-event-listener#content-2 https://esdiscuss.org/topic/weak-event-listener#content-2 > It's hard to find something fresh. I will stir the pot at the July TC39 meeting and get the committee on the record for weak refs with turn-delayed notification, or bust! As recently as September last year you told me it may happen... but with an indeterminate timeframe: https://mail.mozilla.org/pipermail/es-discuss/2014-September/039078.html https://mail.mozilla.org/pipermail/es-discuss/2014-September...
      - BrendanEich 11y ago
        Yeah, it needs an active champion. I'll poke likely champs.
- kevingadd 11y ago
  Weak refs are actually going in??? I got the impression they were dead because TC39 disliked them so much.
krebby 11y ago
You and I had this exact conversation at Eataly a few months back. WeakMaps are cool, but JS is a garbage-collected language. All you have to do to GC something is stop referencing it. WeakMaps are only really useful when you don't control the referenced object's lifecycle. Even then, you can simply invert your map or check in your callback.
- daurnimator 11y ago
  > JS is a garbage-collected language. All you have to do to GC something is stop referencing it. That works well for JS... but if you are trying to use asm.js (or now wasm), you need to act on things getting garbage collected inside of your code.
  - krebby 11y ago
    You're talking about implementing your own GC inside JS. A valid use case, but a niche one. JS the language doesn't really need to expose GC internals. JS the compile target does. (Though it can be worked around).
    - daurnimator 11y ago
      > You're talking about implementing your own GC inside JS. A valid use case, but a niche one. Any asm.js code that calls into DOM apis is going to need this. Otherwise they don't know when to free stuff. Most of the current asm.js code out there just binds a single canvas element, and works with that. But if you want to actually call anything else....

BrendanEich 11y ago

Read up, you've missed a memo :-P. Plan for Harmony-era weak refs is to notify in next event loop turn. Note turn-based notification. No way will exact GC schedule be leaked via callbacks from the GC. Ditto anything like Java's post-mortem finalization. But your "e.g." is unclear, though. Why do you need to manually deallocate a callback function passed to setTimeout?

daurnimator 11y ago
> Read up, you've missed a memo :-P. Plan for Harmony-era weak refs is to notify in next event loop turn. Got a link to the memo? I haven't heard about this one. > Why do you need to manually deallocate a callback function passed to setTimeout? One of my use cases is running lua in the browser. see lua.vm.js: https://kripken.github.io/lua.vm.js/repl.html https://kripken.github.io/lua.vm.js/repl.html When you pass a lua function to a javascript function, I create a 'proxy' object that holds a reference to the function in the lua VM. Only if javascript tells me it's "done" with it can I drop the ref inside the lua VM.
- chadaustin 11y ago
  FWIW, this is exactly the same problem we had with making it possible for Embind to allow passing C++ functions into setTimeout. We'd need to synthesize a JavaScript function that holds a wrapper object for the C++ function, and that wrapper object would need to be deallocated when the timer is done. For general callbacks, this is a hard problem, and finalizers would provide a clean way to solve it.
- BrendanEich 11y ago
  See, e.g., https://esdiscuss.org/topic/weak-event-listener#content-2 https://esdiscuss.org/topic/weak-event-listener#content-2 It's hard to find something fresh. I will stir the pot at the July TC39 meeting and get the committee on the record for weak refs with turn-delayed notification, or bust!
  - daurnimator 11y ago
    > See, e.g., > https://esdiscuss.org/topic/weak-event-listener#content-2 https://esdiscuss.org/topic/weak-event-listener#content-2 > It's hard to find something fresh. I will stir the pot at the July TC39 meeting and get the committee on the record for weak refs with turn-delayed notification, or bust! As recently as September last year you told me it may happen... but with an indeterminate timeframe: https://mail.mozilla.org/pipermail/es-discuss/2014-September/039078.html https://mail.mozilla.org/pipermail/es-discuss/2014-September...
    - BrendanEich 11y ago
      Yeah, it needs an active champion. I'll poke likely champs.
kevingadd 11y ago
Weak refs are actually going in??? I got the impression they were dead because TC39 disliked them so much.

krebby 11y ago

You and I had this exact conversation at Eataly a few months back. WeakMaps are cool, but JS is a garbage-collected language. All you have to do to GC something is stop referencing it. WeakMaps are only really useful when you don't control the referenced object's lifecycle. Even then, you can simply invert your map or check in your callback.

daurnimator 11y ago
> JS is a garbage-collected language. All you have to do to GC something is stop referencing it. That works well for JS... but if you are trying to use asm.js (or now wasm), you need to act on things getting garbage collected inside of your code.
- krebby 11y ago
  You're talking about implementing your own GC inside JS. A valid use case, but a niche one. JS the language doesn't really need to expose GC internals. JS the compile target does. (Though it can be worked around).
  - daurnimator 11y ago
    > You're talking about implementing your own GC inside JS. A valid use case, but a niche one. Any asm.js code that calls into DOM apis is going to need this. Otherwise they don't know when to free stuff. Most of the current asm.js code out there just binds a single canvas element, and works with that. But if you want to actually call anything else....