I had some time tonight and I did some testing of my own.
Apparently, objects whose properties are set inside the literal block do
not share the same hidden map/class with those whose properties are set
later using dot or bracket notation. These latter two however can be used
interchangeably with identical results.
I imagine it was done this way in order to save memory, but it is a
disadvantage when the code has to process structurally identical objects
that are potentially constructed in different places. And the memory
savings are gone in that case as well because there have to be separate
hidden classes for each origin.
I didn't look at the v8 source and I'm only speculating but if this is the
case then perhaps a command line flag that makes literal objects build a
class chain like if one were using dot/bracket notation so that they share
hidden classes would be a neat setting to have for this situation.
On Monday, July 23, 2012 4:15:04 PM UTC-3, Sebastian Ferreyra Pons wrote:
>
> Ok, this means I have a shot at having my code compiled monomorphically by
> creating my objects without prototype, which I don't need anyway because
> such information is useless to me as it's not stored in JSON/BSON.
>
> How about these two objects. would they share the same hidden map?
>
> var o1 = {};
> o1.x = 1;
>
> var o2 = {x:1};
>
> Thanks!
>
> On Monday, July 23, 2012 11:53:20 AM UTC-3, Vyacheslav Egorov wrote:
>>
>> Yes.
>> --
>> Vyacheslav Egorov
>>
>>
>> On Mon, Jul 23, 2012 at 4:48 PM, Sebastian Ferreyra Pons
>> <[email protected]> wrote:
>> >> Yes. In a constructor function, the hidden class begins with an
>> >> element that also includes a prototype. In two different constructor
>> >> functions these initial elements will be different, making their
>> >> hidden classes different.
>> >
>> > Does this mean that if I make sure that both the mongo driver and my
>> code
>> > uses the literal empty object {} for creating new objects they will
>> share
>> > the same root class?
>> >
>> > On Friday, July 20, 2012 2:21:39 AM UTC-3, jMerliN wrote:
>> >>
>> >> Hi Sebastian,
>> >>
>> >> > It is my understanding that hidden classes are not shared between
>> >> > different
>> >> > constructors, even if I construct structurally identical objects
>> with
>> >> > the
>> >> > same properties and in the same order. This seems to imply that
>> >> > deserialized objects coming from mongodb will not share the same
>> hidden
>> >> > class as structurally identical objects created by the constructors,
>> >> > hence
>> >> > functions that use these objects will not be well optimized into
>> native
>> >> > code. Am I right?
>> >>
>> >> Yes. In a constructor function, the hidden class begins with an
>> >> element that also includes a prototype. In two different constructor
>> >> functions these initial elements will be different, making their
>> >> hidden classes different.
>> >>
>> >> If you have hot code that is being impacted because you pass it both
>> >> objects you construct and ones from the MongoDB driver you're using,
>> >> one thing you can do is make your constructor take the MongoDB object
>> >> representation as an input. Then you would be able to make your hot
>> >> code monomorphic. If you don't have any hot code being impacted, it's
>> >> probably not something you should worry about unless your Mongo driver
>> >> is putting objects it constructs into dictionary mode for some reason.
>> >>
>> >> An example: http://jsfiddle.net/xznxP/
>> >>
>> >> "hot" only deoptimizes when given the raw object here, which has a
>> >> different hidden class.
>> >>
>> >> > Is there any hidden class inheritance built into v8? That is, if I
>> >> > create
>> >> > object o={a:1, b:2} and later add o.z=3, will native code optimized
>> for
>> >> > the
>> >> > hidden class before the property-add still work unmodified
>> afterwards?
>> >>
>> >> No.
>> >>
>> >> - Justin
>> >>
>> >> On Jul 19, 4:16 pm, Sebastian Ferreyra Pons <[email protected]>
>> >> wrote:
>> >> > I have two questions.
>> >> >
>> >> > #1
>> >> > I'm developing a Node.js/Mongodb web app.
>> >> >
>> >> > This means that objects used in the code will be created by at least
>> two
>> >> > different code paths:
>> >> >
>> >> > 1. Constructor functions
>> >> > 2. Deserialization code in the mongo driver.
>> >> >
>> >> > It is my understanding that hidden classes are not shared between
>> >> > different
>> >> > constructors, even if I construct structurally identical objects
>> with
>> >> > the
>> >> > same properties and in the same order. This seems to imply that
>> >> > deserialized objects coming from mongodb will not share the same
>> hidden
>> >> > class as structurally identical objects created by the constructors,
>> >> > hence
>> >> > functions that use these objects will not be well optimized into
>> native
>> >> > code. Am I right?
>> >> >
>> >> > #2
>> >> > Is there any hidden class inheritance built into v8? That is, if I
>> >> > create
>> >> > object o={a:1, b:2} and later add o.z=3, will native code optimized
>> for
>> >> > the
>> >> > hidden class before the property-add still work unmodified
>> afterwards?
>> >
>> > --
>> > v8-users mailing list
>> > [email protected]
>> > http://groups.google.com/group/v8-users
>>
>
On Monday, July 23, 2012 4:15:04 PM UTC-3, Sebastian Ferreyra Pons wrote:
>
> Ok, this means I have a shot at having my code compiled monomorphically by
> creating my objects without prototype, which I don't need anyway because
> such information is useless to me as it's not stored in JSON/BSON.
>
> How about these two objects. would they share the same hidden map?
>
> var o1 = {};
> o1.x = 1;
>
> var o2 = {x:1};
>
> Thanks!
>
> On Monday, July 23, 2012 11:53:20 AM UTC-3, Vyacheslav Egorov wrote:
>>
>> Yes.
>> --
>> Vyacheslav Egorov
>>
>>
>> On Mon, Jul 23, 2012 at 4:48 PM, Sebastian Ferreyra Pons
>> <[email protected]> wrote:
>> >> Yes. In a constructor function, the hidden class begins with an
>> >> element that also includes a prototype. In two different constructor
>> >> functions these initial elements will be different, making their
>> >> hidden classes different.
>> >
>> > Does this mean that if I make sure that both the mongo driver and my
>> code
>> > uses the literal empty object {} for creating new objects they will
>> share
>> > the same root class?
>> >
>> > On Friday, July 20, 2012 2:21:39 AM UTC-3, jMerliN wrote:
>> >>
>> >> Hi Sebastian,
>> >>
>> >> > It is my understanding that hidden classes are not shared between
>> >> > different
>> >> > constructors, even if I construct structurally identical objects
>> with
>> >> > the
>> >> > same properties and in the same order. This seems to imply that
>> >> > deserialized objects coming from mongodb will not share the same
>> hidden
>> >> > class as structurally identical objects created by the constructors,
>> >> > hence
>> >> > functions that use these objects will not be well optimized into
>> native
>> >> > code. Am I right?
>> >>
>> >> Yes. In a constructor function, the hidden class begins with an
>> >> element that also includes a prototype. In two different constructor
>> >> functions these initial elements will be different, making their
>> >> hidden classes different.
>> >>
>> >> If you have hot code that is being impacted because you pass it both
>> >> objects you construct and ones from the MongoDB driver you're using,
>> >> one thing you can do is make your constructor take the MongoDB object
>> >> representation as an input. Then you would be able to make your hot
>> >> code monomorphic. If you don't have any hot code being impacted, it's
>> >> probably not something you should worry about unless your Mongo driver
>> >> is putting objects it constructs into dictionary mode for some reason.
>> >>
>> >> An example: http://jsfiddle.net/xznxP/
>> >>
>> >> "hot" only deoptimizes when given the raw object here, which has a
>> >> different hidden class.
>> >>
>> >> > Is there any hidden class inheritance built into v8? That is, if I
>> >> > create
>> >> > object o={a:1, b:2} and later add o.z=3, will native code optimized
>> for
>> >> > the
>> >> > hidden class before the property-add still work unmodified
>> afterwards?
>> >>
>> >> No.
>> >>
>> >> - Justin
>> >>
>> >> On Jul 19, 4:16 pm, Sebastian Ferreyra Pons <[email protected]>
>> >> wrote:
>> >> > I have two questions.
>> >> >
>> >> > #1
>> >> > I'm developing a Node.js/Mongodb web app.
>> >> >
>> >> > This means that objects used in the code will be created by at least
>> two
>> >> > different code paths:
>> >> >
>> >> > 1. Constructor functions
>> >> > 2. Deserialization code in the mongo driver.
>> >> >
>> >> > It is my understanding that hidden classes are not shared between
>> >> > different
>> >> > constructors, even if I construct structurally identical objects
>> with
>> >> > the
>> >> > same properties and in the same order. This seems to imply that
>> >> > deserialized objects coming from mongodb will not share the same
>> hidden
>> >> > class as structurally identical objects created by the constructors,
>> >> > hence
>> >> > functions that use these objects will not be well optimized into
>> native
>> >> > code. Am I right?
>> >> >
>> >> > #2
>> >> > Is there any hidden class inheritance built into v8? That is, if I
>> >> > create
>> >> > object o={a:1, b:2} and later add o.z=3, will native code optimized
>> for
>> >> > the
>> >> > hidden class before the property-add still work unmodified
>> afterwards?
>> >
>> > --
>> > v8-users mailing list
>> > [email protected]
>> > http://groups.google.com/group/v8-users
>>
>
On Monday, July 23, 2012 4:15:04 PM UTC-3, Sebastian Ferreyra Pons wrote:
>
> Ok, this means I have a shot at having my code compiled monomorphically by
> creating my objects without prototype, which I don't need anyway because
> such information is useless to me as it's not stored in JSON/BSON.
>
> How about these two objects. would they share the same hidden map?
>
> var o1 = {};
> o1.x = 1;
>
> var o2 = {x:1};
>
> Thanks!
>
> On Monday, July 23, 2012 11:53:20 AM UTC-3, Vyacheslav Egorov wrote:
>>
>> Yes.
>> --
>> Vyacheslav Egorov
>>
>>
>> On Mon, Jul 23, 2012 at 4:48 PM, Sebastian Ferreyra Pons
>> <[email protected]> wrote:
>> >> Yes. In a constructor function, the hidden class begins with an
>> >> element that also includes a prototype. In two different constructor
>> >> functions these initial elements will be different, making their
>> >> hidden classes different.
>> >
>> > Does this mean that if I make sure that both the mongo driver and my
>> code
>> > uses the literal empty object {} for creating new objects they will
>> share
>> > the same root class?
>> >
>> > On Friday, July 20, 2012 2:21:39 AM UTC-3, jMerliN wrote:
>> >>
>> >> Hi Sebastian,
>> >>
>> >> > It is my understanding that hidden classes are not shared between
>> >> > different
>> >> > constructors, even if I construct structurally identical objects
>> with
>> >> > the
>> >> > same properties and in the same order. This seems to imply that
>> >> > deserialized objects coming from mongodb will not share the same
>> hidden
>> >> > class as structurally identical objects created by the constructors,
>> >> > hence
>> >> > functions that use these objects will not be well optimized into
>> native
>> >> > code. Am I right?
>> >>
>> >> Yes. In a constructor function, the hidden class begins with an
>> >> element that also includes a prototype. In two different constructor
>> >> functions these initial elements will be different, making their
>> >> hidden classes different.
>> >>
>> >> If you have hot code that is being impacted because you pass it both
>> >> objects you construct and ones from the MongoDB driver you're using,
>> >> one thing you can do is make your constructor take the MongoDB object
>> >> representation as an input. Then you would be able to make your hot
>> >> code monomorphic. If you don't have any hot code being impacted, it's
>> >> probably not something you should worry about unless your Mongo driver
>> >> is putting objects it constructs into dictionary mode for some reason.
>> >>
>> >> An example: http://jsfiddle.net/xznxP/
>> >>
>> >> "hot" only deoptimizes when given the raw object here, which has a
>> >> different hidden class.
>> >>
>> >> > Is there any hidden class inheritance built into v8? That is, if I
>> >> > create
>> >> > object o={a:1, b:2} and later add o.z=3, will native code optimized
>> for
>> >> > the
>> >> > hidden class before the property-add still work unmodified
>> afterwards?
>> >>
>> >> No.
>> >>
>> >> - Justin
>> >>
>> >> On Jul 19, 4:16 pm, Sebastian Ferreyra Pons <[email protected]>
>> >> wrote:
>> >> > I have two questions.
>> >> >
>> >> > #1
>> >> > I'm developing a Node.js/Mongodb web app.
>> >> >
>> >> > This means that objects used in the code will be created by at least
>> two
>> >> > different code paths:
>> >> >
>> >> > 1. Constructor functions
>> >> > 2. Deserialization code in the mongo driver.
>> >> >
>> >> > It is my understanding that hidden classes are not shared between
>> >> > different
>> >> > constructors, even if I construct structurally identical objects
>> with
>> >> > the
>> >> > same properties and in the same order. This seems to imply that
>> >> > deserialized objects coming from mongodb will not share the same
>> hidden
>> >> > class as structurally identical objects created by the constructors,
>> >> > hence
>> >> > functions that use these objects will not be well optimized into
>> native
>> >> > code. Am I right?
>> >> >
>> >> > #2
>> >> > Is there any hidden class inheritance built into v8? That is, if I
>> >> > create
>> >> > object o={a:1, b:2} and later add o.z=3, will native code optimized
>> for
>> >> > the
>> >> > hidden class before the property-add still work unmodified
>> afterwards?
>> >
>> > --
>> > v8-users mailing list
>> > [email protected]
>> > http://groups.google.com/group/v8-users
>>
>
On Monday, July 23, 2012 4:15:04 PM UTC-3, Sebastian Ferreyra Pons wrote:
>
> Ok, this means I have a shot at having my code compiled monomorphically by
> creating my objects without prototype, which I don't need anyway because
> such information is useless to me as it's not stored in JSON/BSON.
>
> How about these two objects. would they share the same hidden map?
>
> var o1 = {};
> o1.x = 1;
>
> var o2 = {x:1};
>
> Thanks!
>
> On Monday, July 23, 2012 11:53:20 AM UTC-3, Vyacheslav Egorov wrote:
>>
>> Yes.
>> --
>> Vyacheslav Egorov
>>
>>
>> On Mon, Jul 23, 2012 at 4:48 PM, Sebastian Ferreyra Pons
>> <[email protected]> wrote:
>> >> Yes. In a constructor function, the hidden class begins with an
>> >> element that also includes a prototype. In two different constructor
>> >> functions these initial elements will be different, making their
>> >> hidden classes different.
>> >
>> > Does this mean that if I make sure that both the mongo driver and my
>> code
>> > uses the literal empty object {} for creating new objects they will
>> share
>> > the same root class?
>> >
>> > On Friday, July 20, 2012 2:21:39 AM UTC-3, jMerliN wrote:
>> >>
>> >> Hi Sebastian,
>> >>
>> >> > It is my understanding that hidden classes are not shared between
>> >> > different
>> >> > constructors, even if I construct structurally identical objects
>> with
>> >> > the
>> >> > same properties and in the same order. This seems to imply that
>> >> > deserialized objects coming from mongodb will not share the same
>> hidden
>> >> > class as structurally identical objects created by the constructors,
>> >> > hence
>> >> > functions that use these objects will not be well optimized into
>> native
>> >> > code. Am I right?
>> >>
>> >> Yes. In a constructor function, the hidden class begins with an
>> >> element that also includes a prototype. In two different constructor
>> >> functions these initial elements will be different, making their
>> >> hidden classes different.
>> >>
>> >> If you have hot code that is being impacted because you pass it both
>> >> objects you construct and ones from the MongoDB driver you're using,
>> >> one thing you can do is make your constructor take the MongoDB object
>> >> representation as an input. Then you would be able to make your hot
>> >> code monomorphic. If you don't have any hot code being impacted, it's
>> >> probably not something you should worry about unless your Mongo driver
>> >> is putting objects it constructs into dictionary mode for some reason.
>> >>
>> >> An example: http://jsfiddle.net/xznxP/
>> >>
>> >> "hot" only deoptimizes when given the raw object here, which has a
>> >> different hidden class.
>> >>
>> >> > Is there any hidden class inheritance built into v8? That is, if I
>> >> > create
>> >> > object o={a:1, b:2} and later add o.z=3, will native code optimized
>> for
>> >> > the
>> >> > hidden class before the property-add still work unmodified
>> afterwards?
>> >>
>> >> No.
>> >>
>> >> - Justin
>> >>
>> >> On Jul 19, 4:16 pm, Sebastian Ferreyra Pons <[email protected]>
>> >> wrote:
>> >> > I have two questions.
>> >> >
>> >> > #1
>> >> > I'm developing a Node.js/Mongodb web app.
>> >> >
>> >> > This means that objects used in the code will be created by at least
>> two
>> >> > different code paths:
>> >> >
>> >> > 1. Constructor functions
>> >> > 2. Deserialization code in the mongo driver.
>> >> >
>> >> > It is my understanding that hidden classes are not shared between
>> >> > different
>> >> > constructors, even if I construct structurally identical objects
>> with
>> >> > the
>> >> > same properties and in the same order. This seems to imply that
>> >> > deserialized objects coming from mongodb will not share the same
>> hidden
>> >> > class as structurally identical objects created by the constructors,
>> >> > hence
>> >> > functions that use these objects will not be well optimized into
>> native
>> >> > code. Am I right?
>> >> >
>> >> > #2
>> >> > Is there any hidden class inheritance built into v8? That is, if I
>> >> > create
>> >> > object o={a:1, b:2} and later add o.z=3, will native code optimized
>> for
>> >> > the
>> >> > hidden class before the property-add still work unmodified
>> afterwards?
>> >
>> > --
>> > v8-users mailing list
>> > [email protected]
>> > http://groups.google.com/group/v8-users
>>
>
--
v8-users mailing list
[email protected]
http://groups.google.com/group/v8-users
