Re: Weak References

2015-09-07 Thread Isiah Meadows 
Resending this as a new message because of my apparently broken
WYSIWYDG (what you see is what you don't get) email client... :-(

Hopefully this doesn't itself get corrupted...

> My original email featured a use case, although I had to rewrite it to use 
> explicit garbage collection. I need a way to watch for when the object is 
> garbage collected.
>
> ```js
> function rotateStream(interval, format) {
> const res = {}
> setStream(res, format)
>
> let stream = new WeakReference(res) , format)
>
> let timer = setInterval(() => {
> setStream(stream.get(), format)
> }, interval)
>
> stream.onCollect(() => {
> // reference is dead, clear this timer
> clearTimer(timer)
> // break local strong references
> timer = stream = null
> })
>
> // Return a strong reference
> return res
> }
> ```
>
> The complicating part is that I also need the interval callback to weakly 
> reference the value. Otherwise, I've always got one active strong reference 
> to the stream. This is with a listener for when the value is garbage 
> collected.
>
> Here's the version without a listener (it's simpler, but more crude):
>
> ```js
> function rotateStream(interval, format) {
> const res = {}
> setStream(res, format)
>
> let stream = new WeakReference(res)
>
> setInterval(function () {
> try {
> setStream(stream.get(), format)
> } catch (e) {
> // reference is dead, clear this timer
> clearInterval(this)
>
> // break strong reference to weak one
> stream = null
> }
> }, interval)
>
> // Return a strong reference
> return res
> }
> ```
>
> Sorry for the ambiguity.
>
> (edited out a few bugs from the original)

(it got corrupted when saving somehow :-( )


On Sun, Sep 6, 2015 at 11:34 PM, Mark S. Miller  wrote:
>
>
> On Sun, Sep 6, 2015 at 8:04 PM, Isiah Meadows 
> wrote:
>>
>> My original email featured a use case, although I had to rewrite it to use
>> explicit garbage collection. I need a way to watch for when the object is
>> garbage collected.
>>
>> ```js
>
> [...Somehow reformatted in transit...]
>
>>
>> ```
>
>
> Hi Isiah, the text in the above code block somehow got reformatted in
> transit. You can see the problem at
> https://mail.mozilla.org/pipermail/es-discuss/2015-September/044141.html
> https://esdiscuss.org/topic/weak-references#content-10
>
> Since the code below does not have the callback, I don't yet have enough
> context to understand your message. When the GC notifies that the stream is
> to be collected, by notifying some callback, why does that callback need to
> access the stream? What does the callback do with the stream during the
> notification that the stream is condemned?
>
> Is the interval callback somehow related to the GC notification callback? As
> you see, I just don't get it yet.
>>
>>
>> The complicating part is that I also need the interval callback to weakly
>> reference the value. Otherwise, I've always got one active strong reference
>> to the stream. This is with a listener for when the value is garbage
>> collected.
>>
>> Here's the version without a listener (it's simpler, but more crude):
>>
>> ```js
>> function rotateStream(interval, format) {
>> const res = {}
>> setStream(res, format)
>>
>> let stream = new WeakReference(res)
>>
>> setInterval(function () {
>> try {
>> setStream(stream.get(), format)
>> } catch (e) {
>> // reference is dead, clear this timer
>> clearInterval(this)
>>
>> // break strong reference to weak one
>> stream = null
>> }
>> }, interval)
>>
>> // Return a strong reference
>> return res
>> }
>> ```
>>
>> Sorry for the ambiguity.
>>
>> (edited out a few bugs from the original)
>>
>>
>
> --
> Cheers,
> --MarkM



-- 
Isiah Meadows
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Re: Weak References

2015-09-07 Thread Mark S. Miller 
On Mon, Sep 7, 2015 at 10:19 AM, Isiah Meadows 
wrote:

> Resending this as a new message because of my apparently broken
> WYSIWYDG (what you see is what you don't get) email client... :-(
>
> Hopefully this doesn't itself get corrupted...
>
> > My original email featured a use case, although I had to rewrite it to
> use explicit garbage collection. I need a way to watch for when the object
> is garbage collected.
> >
> > ```js
> > function rotateStream(interval, format) {
> > const res = {}
> > setStream(res, format)
> >
> > let stream = new WeakReference(res) , format)
>

Unbalanced parens.


> >
> > let timer = setInterval(() => {
> > setStream(stream.get(), format)
> > }, interval)
> >
> > stream.onCollect(() => {
> > // reference is dead, clear this timer
> > clearTimer(timer)
> > // break local strong references
> > timer = stream = null
> > })
> >
> > // Return a strong reference
> > return res
> > }
> > ```
> >
> > The complicating part is that I also need the interval callback to
> weakly reference the value. Otherwise, I've always got one active strong
> reference to the stream. This is with a listener for when the value is
> garbage collected.
> >
> > Here's the version without a listener (it's simpler, but more crude):
> >
> > ```js
> > function rotateStream(interval, format) {
> > const res = {}
> > setStream(res, format)
> >
> > let stream = new WeakReference(res)
> >
> > setInterval(function () {
> > try {
> > setStream(stream.get(), format)
> > } catch (e) {
> > // reference is dead, clear this timer
> > clearInterval(this)
> >
> > // break strong reference to weak one
> > stream = null
> > }
> > }, interval)
> >
> > // Return a strong reference
> > return res
> > }
> > ```
> >
> > Sorry for the ambiguity.
> >
> > (edited out a few bugs from the original)
>
> (it got corrupted when saving somehow :-( )
>
>
> On Sun, Sep 6, 2015 at 11:34 PM, Mark S. Miller 
> wrote:
> >
> >
> > On Sun, Sep 6, 2015 at 8:04 PM, Isiah Meadows 
> > wrote:
> >>
> >> My original email featured a use case, although I had to rewrite it to
> use
> >> explicit garbage collection. I need a way to watch for when the object
> is
> >> garbage collected.
> >>
> >> ```js
> >
> > [...Somehow reformatted in transit...]
> >
> >>
> >> ```
> >
> >
> > Hi Isiah, the text in the above code block somehow got reformatted in
> > transit. You can see the problem at
> > https://mail.mozilla.org/pipermail/es-discuss/2015-September/044141.html
> > https://esdiscuss.org/topic/weak-references#content-10
> >
> > Since the code below does not have the callback, I don't yet have enough
> > context to understand your message. When the GC notifies that the stream
> is
> > to be collected, by notifying some callback, why does that callback need
> to
> > access the stream? What does the callback do with the stream during the
> > notification that the stream is condemned?
> >
> > Is the interval callback somehow related to the GC notification
> callback? As
> > you see, I just don't get it yet.
> >>
> >>
> >> The complicating part is that I also need the interval callback to
> weakly
> >> reference the value. Otherwise, I've always got one active strong
> reference
> >> to the stream. This is with a listener for when the value is garbage
> >> collected.
> >>
> >> Here's the version without a listener (it's simpler, but more crude):
> >>
> >> ```js
> >> function rotateStream(interval, format) {
> >> const res = {}
> >> setStream(res, format)
> >>
> >> let stream = new WeakReference(res)
> >>
> >> setInterval(function () {
> >> try {
> >> setStream(stream.get(), format)
> >> } catch (e) {
> >> // reference is dead, clear this timer
> >> clearInterval(this)
> >>
> >> // break strong reference to weak one
> >> stream = null
> >> }
> >> }, interval)
> >>
> >> // Return a strong reference
> >> return res
> >> }
> >> ```
> >>
> >> Sorry for the ambiguity.
> >>
> >> (edited out a few bugs from the original)
> >>
> >>
> >
> > --
> > Cheers,
> > --MarkM
>
>
>
> --
> Isiah Meadows
>



-- 
Cheers,
--MarkM
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Re: Weak References

2015-09-07 Thread Mark S. Miller 
I also don't get the purpose of this code. What is it trying to achieve?
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Re: Weak References

2015-09-07 Thread Isiah Meadows 
It's replacing the prototype of a stream periodically to point to a new
writable file output stream pointing to a new file, but I want to kill the
interval timer when the object is garbage collected.

Something like this:

1. Create new stream.
2. Point it to a log file.
3. Every tick on a given interval, do this:
3.1. Change the destination of the stream to a new log file.
4. When the stream itself is GC'd, do this:
4.1. Clear the timer.
4.2. Clear all local references to both the timer and the stream.
5. Return the stream.

The catch is that I don't want the stream strongly referenced in any local
closures because it would end up never being collected - there would always
be an active strong reference to it. I don't think a
`Reflect.onOnlyOneReferenceLeft(obj, callback)` would make it into the
language, so weak references are the best way to avoid this. And if I were
doing this in Java or C++, I would most definitely use weak
references/pointers for this use case. (This is out of the land of what
automatic garbage collection can handle at this point.)

On Mon, Sep 7, 2015, 13:33 Mark S. Miller  wrote:

> I also don't get the purpose of this code. What is it trying to achieve?
>
>
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Re: Weak References

2015-09-07 Thread Mark S. Miller 
function rotateStreamHelper(weakRes, interval, format) {
  let timer = setInterval(() => setStream(weakRes.get(), format),
  interval);
  weakRes.register(() => clearInterval(timer));
}

function rotateStream(interval, format) {
  const res = {};
  setStream(res, format);

  rotateStreamHelper(new WeakRef(res), interval, format);

  // Return a strong reference
  return res;
}


Given
http://wiki.ecmascript.org/doku.php?id=strawman:weak_references
does this implement your intention?



On Mon, Sep 7, 2015 at 10:53 AM, Isiah Meadows 
wrote:

> It's replacing the prototype of a stream periodically to point to a new
> writable file output stream pointing to a new file, but I want to kill the
> interval timer when the object is garbage collected.
>
> Something like this:
>
> 1. Create new stream.
> 2. Point it to a log file.
> 3. Every tick on a given interval, do this:
> 3.1. Change the destination of the stream to a new log file.
> 4. When the stream itself is GC'd, do this:
> 4.1. Clear the timer.
> 4.2. Clear all local references to both the timer and the stream.
> 5. Return the stream.
>
> The catch is that I don't want the stream strongly referenced in any local
> closures because it would end up never being collected - there would always
> be an active strong reference to it. I don't think a
> `Reflect.onOnlyOneReferenceLeft(obj, callback)` would make it into the
> language, so weak references are the best way to avoid this. And if I were
> doing this in Java or C++, I would most definitely use weak
> references/pointers for this use case. (This is out of the land of what
> automatic garbage collection can handle at this point.)
>
> On Mon, Sep 7, 2015, 13:33 Mark S. Miller  wrote:
>
>> I also don't get the purpose of this code. What is it trying to achieve?
>>
>>


-- 
Cheers,
--MarkM
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Re: Weak References

2015-09-07 Thread Isiah Meadows 
Yes.

On Mon, Sep 7, 2015, 14:30 Mark S. Miller  wrote:

> function rotateStreamHelper(weakRes, interval, format) {
>   let timer = setInterval(() => setStream(weakRes.get(), format),
>   interval);
>   weakRes.register(() => clearInterval(timer));
> }
>
> function rotateStream(interval, format) {
>   const res = {};
>   setStream(res, format);
>
>   rotateStreamHelper(new WeakRef(res), interval, format);
>
>   // Return a strong reference
>   return res;
> }
>
>
> Given
> http://wiki.ecmascript.org/doku.php?id=strawman:weak_references
> does this implement your intention?
>
>
>
> On Mon, Sep 7, 2015 at 10:53 AM, Isiah Meadows 
> wrote:
>
>> It's replacing the prototype of a stream periodically to point to a new
>> writable file output stream pointing to a new file, but I want to kill the
>> interval timer when the object is garbage collected.
>>
>> Something like this:
>>
>> 1. Create new stream.
>> 2. Point it to a log file.
>> 3. Every tick on a given interval, do this:
>> 3.1. Change the destination of the stream to a new log file.
>> 4. When the stream itself is GC'd, do this:
>> 4.1. Clear the timer.
>> 4.2. Clear all local references to both the timer and the stream.
>> 5. Return the stream.
>>
>> The catch is that I don't want the stream strongly referenced in any
>> local closures because it would end up never being collected - there would
>> always be an active strong reference to it. I don't think a
>> `Reflect.onOnlyOneReferenceLeft(obj, callback)` would make it into the
>> language, so weak references are the best way to avoid this. And if I were
>> doing this in Java or C++, I would most definitely use weak
>> references/pointers for this use case. (This is out of the land of what
>> automatic garbage collection can handle at this point.)
>>
>> On Mon, Sep 7, 2015, 13:33 Mark S. Miller  wrote:
>>
>>> I also don't get the purpose of this code. What is it trying to achieve?
>>>
>>>
>
>
> --
> Cheers,
> --MarkM
>
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