Exposing object handles to userland

8 years ago by tyson andre — view source — reply

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There was a proposal back in 2015 to implement
a function spl_object_id(object $o) : int, which directly returns the object handle (similar tospl_object_hash`, but as an integer, not a string).
I'm interested in finishing implementing spl_object_id for php 7.2

I already have working code implementing spl_object_id() at
https://github.com/TysonAndre/php-src/pull/1
The implementation XORs the object handle with the
exact same random bits that spl_object_hash would.

Previous emails from 2015 can be seen here:

https://marc.info/?t=143835274500003&r=1&w=2

Previous comment by a PHP maintainer in support of spl_object_id()

https://marc.info/?l=php-internals&m=143837339210596&w=2

I'm unsure if an RFC is necessary. I have two pending questions.

Can two objects can have the same object id
but different object handlers?
(e.g. iterators of some built in classes?)
I'm not familiar enough with PHP's history to be sure.
Can the the largest object handle be larger
than the size of zend_long in 32-bit systems?

Example places where this would be useful:

https://marc.info/?l=php-internals&m=143849841618494&w=2
I also recently wanted to track a large number of (cloneable)
small sets of objects in an application that sometimes used a lot of memory,
and the fact that arrays support copy on write helped save memory
relative to SplObjectHash if arrays and integer keys were used.
See https://github.com/etsy/phan/pull/729#issuecomment-299289378

Tyson Andre (tandre)

8 years ago by Stanislav Malyshev — view source — reply

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Hi!

Can two objects can have the same object id
but different object handlers?
(e.g. iterators of some built in classes?)
I'm not familiar enough with PHP's history to be sure.

Yes, if extension using non-standard handlers is in use.

Can the the largest object handle be larger
than the size of zend_long in 32-bit systems?

Handle is uint32_t, so probably no.

--
Stas Malyshev
smalyshev@gmail.com

8 years ago by Anatol Belski — view source — reply

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Hi,

-----Original Message-----
From: Stanislav Malyshev [mailto:smalyshev@gmail.com]
Sent: Wednesday, July 5, 2017 5:28 AM
To: tyson andre tysonandre775@hotmail.com; internals@lists.php.net
Subject: Re: [PHP-DEV] Exposing object handles to userland

Hi!

Can two objects can have the same object id
but different object handlers?
(e.g. iterators of some built in classes?)
I'm not familiar enough with PHP's history to be sure.

Yes, if extension using non-standard handlers is in use.

Can the the largest object handle be larger
than the size of zend_long in 32-bit systems?

Handle is uint32_t, so probably no.

On 32-bit zend_long is a signed 32-bit int, so it can theoretically overflow, while sizeof is same.

Regards

Anatol

8 years ago by Stanislav Malyshev — view source — reply

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Hi!

On 32-bit zend_long is a signed 32-bit int, so it can theoretically overflow, while sizeof is same.

Well, it's the same issue we having on representing any unsigned values,
I guess. Since int<->uint in this case is one-to-one, should be ok to
just use the negative nums, if they are used as IDs and not to calculate
anything, etc. So I don't think it's much of a problem here.

--
Stas Malyshev
smalyshev@gmail.com

8 years ago by Nikita Popov — view source — reply

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On Wed, Jul 5, 2017 at 2:01 AM, tyson andre tysonandre775@hotmail.com
wrote:

There was a proposal back in 2015 to implement
a function spl_object_id(object $o) : int, which directly returns the object handle (similar tospl_object_hash`, but as an integer, not a string).
I'm interested in finishing implementing spl_object_id for php 7.2

I already have working code implementing spl_object_id() at
https://github.com/TysonAndre/php-src/pull/1
The implementation XORs the object handle with the
exact same random bits that spl_object_hash would.

You can drop the masking. It was never effective at what it's supposed to
do (hide memory addresses), but as this is the object ID only, it is
completely unnecessary here.

Previous emails from 2015 can be seen here:

https://marc.info/?t=143835274500003&r=1&w=2

Previous comment by a PHP maintainer in support of spl_object_id()

https://marc.info/?l=php-internals&m=143837339210596&w=2

I'm unsure if an RFC is necessary. I have two pending questions.

I'm +1 on the addition and would be fine with including it without RFC, if
there are no objections on internals.

Can two objects can have the same object id
but different object handlers?
(e.g. iterators of some built in classes?)
I'm not familiar enough with PHP's history to be sure.

No: In PHP 7 this is not possible, which is also why spl_object_hash() no
longer includes the handlers.

Can the the largest object handle be larger
than the size of zend_long in 32-bit systems?

Only in the sense that it could theoretically wrap around to negative
numbers. Of course those would still serve as IDs just as well.

Example places where this would be useful:

https://marc.info/?l=php-internals&m=143849841618494&w=2

I also recently wanted to track a large number of (cloneable)
small sets of objects in an application that sometimes used a lot of
memory,
and the fact that arrays support copy on write helped save memory
relative to SplObjectHash if arrays and integer keys were used.
See https://github.com/etsy/phan/pull/729#issuecomment-299289378

Tyson Andre (tandre)

8 years ago by Stanislav Malyshev — view source — reply

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Hi!

No: In PHP 7 this is not possible, which is also why spl_object_hash() no
longer includes the handlers.

Ah, I missed that part.

--
Stas Malyshev
smalyshev@gmail.com

8 years ago by Sara Golemon — view source — reply

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I'm unsure if an RFC is necessary. I have two pending questions.

Unless someone insists upon it, I'll put my release manager hat on and
say I'm fine with it just going in without an RFC.

-Sara

8 years ago by tyson andre — view source — reply

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Updated https://github.com/TysonAndre/php-src/pull/1 , which is now much shorter.

In response to Nikita Popov's comments:

I'm +1 on the addition and would be fine with including it without RFC, if
there are no objections on internals.

How long should I wait to see if there are objections before creating a pull request?

Can two objects can have the same object id
but different object handlers?
No: In PHP 7 this is not possible, which is also why spl_object_hash() no
longer includes the handlers.

True. Checking again, the implementation of spl_object_hash
doesn't include the handlers, so I don't need to worry.

You can drop the masking. It was never effective at what it's supposed to
do (hide memory addresses), but as this is the object ID only, it is
completely unnecessary here.
[...]
Only in the sense that it could theoretically wrap around to negative
numbers. Of course those would still serve as IDs just as well.

That makes sense. I'm omitting the XOR
(and returning the unobfuscated object handle/id)
in the proposed change, then.

8 years ago by michal.brzuchalski@gmail.com — view source — reply

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06.07.2017 07:24 "tyson andre" tysonandre775@hotmail.com napisał(a):

Updated https://github.com/TysonAndre/php-src/pull/1 , which is now much
shorter.

In response to Nikita Popov's comments:

I'm +1 on the addition and would be fine with including it without RFC,
if
there are no objections on internals.

How long should I wait to see if there are objections before creating a
pull request?

AFAIK you can create PR any time.

Can two objects can have the same object id
but different object handlers?
No: In PHP 7 this is not possible, which is also why spl_object_hash()
no
longer includes the handlers.

True. Checking again, the implementation of spl_object_hash
doesn't include the handlers, so I don't need to worry.

You can drop the masking. It was never effective at what it's supposed
to
do (hide memory addresses), but as this is the object ID only, it is
completely unnecessary here.
[...]
Only in the sense that it could theoretically wrap around to negative
numbers. Of course those would still serve as IDs just as well.

That makes sense. I'm omitting the XOR
(and returning the unobfuscated object handle/id)
in the proposed change, then.

8 years ago by tyson andre — view source — reply

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How long should I wait to see if there are objections before creating a pull request?
AFAIK you can create PR any time.

I created a PR implementing spl_object_id(object $o) : int several days ago,
at https://github.com/php/php-src/pull/2611

8 years ago by Marco Pivetta — view source — reply

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Asking here, since it's not clear to me: is this a good/fitting replacement
for spl_object_hash()?

How long should I wait to see if there are objections before creating a
pull request?
AFAIK you can create PR any time.

I created a PR implementing spl_object_id(object $o) : int several days
ago,
at https://github.com/php/php-src/pull/2611

8 years ago by Nikita Popov — view source — reply

unread

Asking here, since it's not clear to me: is this a good/fitting
replacement for spl_object_hash()?

How long should I wait to see if there are objections before creating
a pull request?
AFAIK you can create PR any time.

I created a PR implementing spl_object_id(object $o) : int several days
ago,
at https://github.com/php/php-src/pull/2611

Yes. spl_object_id() provides the same guarantees as spl_object_hash() --
but is much faster and has a more compact output (an integer instead of an
iirc 32 byte string).

Nikita

8 years ago by Benjamin Eberlei — view source — reply

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On Tue, Jul 11, 2017 at 11:52 AM, Marco Pivetta ocramius@gmail.com
wrote:

Asking here, since it's not clear to me: is this a good/fitting
replacement for spl_object_hash()?

How long should I wait to see if there are objections before creating
a pull request?
AFAIK you can create PR any time.

I created a PR implementing spl_object_id(object $o) : int several days
ago,
at https://github.com/php/php-src/pull/2611

Yes. spl_object_id() provides the same guarantees as spl_object_hash() --
but is much faster and has a more compact output (an integer instead of an
iirc 32 byte string).

Just to clarify, that means object ids are still re-used between objects if
one gets destroyed? The initial bug report was about creating a second
function that solves this problem.

Nikita

8 years ago by tyson andre — view source — reply

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Just to clarify, that means object ids are still re-used between
objects if one gets destroyed?
The initial bug report was about creating a second function that solves this problem.

Correct. This is intended to return the object handles.
The most recent discussion from 2015 was only about object handles.
An intended side effect is that object ids are re-used, the same way spl_object_hash is reused.

i.e. this is not intended to solve https://bugs.php.net/bug.php?id=52657 , and NEWS should not link to that bug id.

Having unique integers wouldn't work as an integer in long runs of processes 32-bit builds

After ~4 billion objects were constructed, the 32-bit integer would be reused.

As for a globally unique object id (let's call that spl_object_uuid),
I don't think it'll ever get included.
I also don't have any need for it.

It would require adding an additional field to zend_object,
which would hurt performance and increase overall memory usage
(e.g. increasing 64-bit integer)
No other programming languages I'm aware of have that
(globally unique object id, even after object is garbage collected)
as a native feature.

Exposing object handles to userland

I created a PR implementing spl_object_id(object $o) : int several days ago, at https://github.com/php/php-src/pull/2611

I created a PR implementing spl_object_id(object $o) : int several days ago, at https://github.com/php/php-src/pull/2611

I created a PR implementing spl_object_id(object $o) : int several days
ago,
at https://github.com/php/php-src/pull/2611

I created a PR implementing spl_object_id(object $o) : int several days
ago,
at https://github.com/php/php-src/pull/2611