$this->this and avoiding circular references

19 years ago by Alan Pinstein — view source

unread

Hi all-

I've been trying to avoid circular references in some data import
scripts and finally figured out how to do it. However, I wanted to
ask you guys to make sure that what I'm doing is something that's
legit and can be relied on into the future.

Also, please note that I tried searching the archives for "this" and
"this->this" but the searcher keeps removing "this" from my query! So
sorry if this is asked and answered....

So, my objects are in a parent-child relationship and they both have
links to each other... pretty standard circular reference scenario:

ParentObject:

function addChildObject($c)
{
$this->children[] = $c;
$c->setParent($this->this); // this syntax is the only way I
found to make "$this" not get refcounted here
}

Now, to make this work as it should without incrementing the ref
counts when storing the link to the parent, setParent() needs to
have a non-refcounted pointer to the object:

ChildObject:

// need & in both places to make the ref not get ref-counted
function setParent(&$parent)
{
$this->-parent = &$parent;
}

My question is, is "$this->this" valid syntax? Can it be relied on?
Is my overall approach sane?

It's very important that I get memory management working in such a
way here because the objects are used in large loops for importing
data, and without this, the script uses unbounded amounts of memory.
With this, it uses a finite amount of memory and works beautifully.

Thanks in advance,
Alan

19 years ago by Jochem Maas — view source

unread

are you using ph4 or php5?
are you setting $this->this yourself or 'is it just there'?

Alan Pinstein wrote:

Hi all-

I've been trying to avoid circular references in some data import
scripts and finally figured out how to do it. However, I wanted to ask
you guys to make sure that what I'm doing is something that's legit and
can be relied on into the future.

Also, please note that I tried searching the archives for "this" and
"this->this" but the searcher keeps removing "this" from my query! So
sorry if this is asked and answered....

So, my objects are in a parent-child relationship and they both have
links to each other... pretty standard circular reference scenario:

ParentObject:

function addChildObject($c)
{
$this->children[] = $c;
$c->setParent($this->this); // this syntax is the only way

assuming php4, I would say this these lines should be (difficult
to tell though, without more insight/code/brains to play with ;-):

function addChildObject(&$c) {
$this->children[] =& $c;
$c->setParent( $this );
}

I found to make "$this" not get refcounted here
}

Now, to make this work as it should without incrementing the ref
counts when storing the link to the parent, setParent() needs to have
a non-refcounted pointer to the object:

ChildObject:

// need & in both places to make the ref not get ref-counted
function setParent(&$parent)
{
$this->-parent = &$parent;
}

My question is, is "$this->this" valid syntax? Can it be relied on? Is
my overall approach sane?

It's very important that I get memory management working in such a way
here because the objects are used in large loops for importing data,
and without this, the script uses unbounded amounts of memory. With
this, it uses a finite amount of memory and works beautifully.

Thanks in advance,
Alan

19 years ago by Alan Pinstein — view source

unread

are you using ph4 or php5?

PHP5

are you setting $this->this yourself or 'is it just there'?

No, I'm not setting it, just reading it (see addChildObject() code
below), if that's what you mean.

-Alan

Alan Pinstein wrote:

Hi all-
I've been trying to avoid circular references in some data import
scripts and finally figured out how to do it. However, I wanted
to ask you guys to make sure that what I'm doing is something
that's legit and can be relied on into the future.
Also, please note that I tried searching the archives for "this"
and "this->this" but the searcher keeps removing "this" from my
query! So sorry if this is asked and answered....
So, my objects are in a parent-child relationship and they both
have links to each other... pretty standard circular reference
scenario:

ParentObject:

function addChildObject($c)
{
$this->children[] = $c;
$c->setParent($this->this); // this syntax is the only
way

assuming php4, I would say this these lines should be (difficult
to tell though, without more insight/code/brains to play with ;-):

function addChildObject(&$c) {
$this->children[] =& $c;
$c->setParent( $this );
}

I found to make "$this" not get refcounted here
}

Now, to make this work as it should without incrementing the ref
counts when storing the link to the parent, setParent() needs to
have a non-refcounted pointer to the object:

ChildObject:

// need & in both places to make the ref not get ref-counted
function setParent(&$parent)
{
$this->-parent = &$parent;
}
My question is, is "$this->this" valid syntax? Can it be relied
on? Is my overall approach sane?
It's very important that I get memory management working in such
a way here because the objects are used in large loops for
importing data, and without this, the script uses unbounded
amounts of memory. With this, it uses a finite amount of memory
and works beautifully.
Thanks in advance,
Alan

19 years ago by Antony Dovgal — view source

unread

Hi all-

<skip>

Please use php-general@lists.php.net for questions regarding development in PHP.

--
Wbr,
Antony Dovgal

19 years ago by dz@bitxtender.com — view source

unread

I don't think PHP-general would be of much help here. After all, his
question was whether this behavior is intentional or not, and if it
can be relied upon in the future. To me, it's an engine thing. And
I'm interested in what the devs can say about this, too.

David

Am 07.12.2005 um 17:27 schrieb Antony Dovgal:

Hi all-

<skip>
Please use php-general@lists.php.net for questions regarding
development in PHP.

Wbr, Antony Dovgal

19 years ago by Roman Ivanov — view source

unread

Antony Dovgal wrote:

Hi all-

<skip>
Please use php-general@lists.php.net for questions regarding development
in PHP.

Please stop bashing other people's messages for the sole reason they do
not deal with C code. The question was perfectly relevant.

19 years ago by Alan Pinstein — view source

unread

Well I posted there first, and someone helped me believe that & on
objects does indeed legitimately not bump the refcount, but no one
knows about $this->this. And there's another similar thread on the
dev list anyway which was answered usefully: http://
aspn.activestate.com/ASPN/Mail/Message/php-Dev/1555640

Plus, this is kind of an internals question because the topic not
documented publicly and it has to do with things that are opaque to
userland like refcounts and how "$this" works.

Alan

Hi all-

<skip>
Please use php-general@lists.php.net for questions regarding
development in PHP.

Wbr, Antony Dovgal

19 years ago by Alan Pinstein — view source

unread

My question is closely related to the one discussed on this php-dev
thread:

http://thread.gmane.org/gmane.comp.php.devel/32430

Someone just sent me this link, which I didn't find myself when
searching b/c the searches strip "this" from queries.

Anyway, the question is related to reference counting of objects when
assigned by value and by reference. It is a very important OO topic
as the ability to have a non-ref-counted object "handle" is basically
requisite to prevent circular reference deadlocks in OO projects.

If the way I have proposed doesn't work, then what is the official
way? And there must be one, otherwise, there is no way to avoid
huge memory leaks (deferred release until end-of-script, I know, but
it's a memory leak in the context of the script while it's running)
with this kind of OO arrangement.

In particular what confuses me is, why does, at least on PHP 5.0.4,
this:

$obj = &$this->this; // doesn't seem to increment the refcount of the
object

behaves differently from:

$obj = &$this; // does seem to increment the refcount to the object

References to $this should not only be valid, but are pretty much
required for proper memory management in an OO environment, unless
there is some other sanctioned way to get a weak reference... now I
am not sure if the fact that making a & reference to an object
doesn't increment the refcount is intended behavior, or an unintended
side effect that may change. This is one of my major questions.

Also, in regards to the thread linked above, I'd say that making &
$this an error is not desirable behavior; but maybe changing the
value of $this should be (ie in C terms, $this is not an lvalue).
Although, in C++/Obj-C you can even change this/self... in fact
it's common in Obj-C:

(id) init
{
if (self = [super init]) { /* etc */ }
return self;
}

Of course PHP is not Obj-C, but it's OO and garbage collected in a
similar way, so PHP has the same need for manipulating $this; that
is, creating weak references.

Alan

Hi all-

<skip>
Please use php-general@lists.php.net for questions regarding
development in PHP.

Wbr, Antony Dovgal

19 years ago by Andi Gutmans — view source

unread

Hi Alan,

Generally speaking, if you create a circular reference (whether by
reference or by value), then you will have a "memory leak" until the
end of the request. This is not only true for objects (and circular
references might be indirect) but also for arrays.
This is a side-effect of reference counting systems, but within the
way PHP is used within a request/response paradigm, it shouldn't be a
real limiting factor in real-life usage. On the contrary, for these
kind of apps, garbage collecting systems have potential to be
significantly slower.

Andi

At 08:15 PM 12/7/2005, Alan Pinstein wrote:

My question is closely related to the one discussed on this php-dev
thread:

http://thread.gmane.org/gmane.comp.php.devel/32430

Someone just sent me this link, which I didn't find myself when
searching b/c the searches strip "this" from queries.

Anyway, the question is related to reference counting of objects when
assigned by value and by reference. It is a very important OO topic
as the ability to have a non-ref-counted object "handle" is basically
requisite to prevent circular reference deadlocks in OO projects.

If the way I have proposed doesn't work, then what is the official
way? And there must be one, otherwise, there is no way to avoid
huge memory leaks (deferred release until end-of-script, I know, but
it's a memory leak in the context of the script while it's running)
with this kind of OO arrangement.

In particular what confuses me is, why does, at least on PHP 5.0.4,
this:

$obj = &$this->this; // doesn't seem to increment the refcount of the
object

behaves differently from:

$obj = &$this; // does seem to increment the refcount to the object

References to $this should not only be valid, but are pretty much
required for proper memory management in an OO environment, unless
there is some other sanctioned way to get a weak reference... now I
am not sure if the fact that making a & reference to an object
doesn't increment the refcount is intended behavior, or an unintended
side effect that may change. This is one of my major questions.

Also, in regards to the thread linked above, I'd say that making &
$this an error is not desirable behavior; but maybe changing the
value of $this should be (ie in C terms, $this is not an lvalue).
Although, in C++/Obj-C you can even change this/self... in fact
it's common in Obj-C:

(id) init
{
if (self = [super init]) { /* etc */ }
return self;
}

Of course PHP is not Obj-C, but it's OO and garbage collected in a
similar way, so PHP has the same need for manipulating $this; that
is, creating weak references.

Alan

Hi all-

<skip>
Please use php-general@lists.php.net for questions regarding
development in PHP.

Wbr, Antony Dovgal

19 years ago by Alan Pinstein — view source

unread

Generally speaking, if you create a circular reference (whether by
reference or by value), then you will have a "memory leak" until
the end of the request. This is not only true for objects (and
circular references might be indirect) but also for arrays.

sure, of course...

This is a side-effect of reference counting systems, but within the
way PHP is used within a request/response paradigm, it shouldn't be
a real limiting factor in real-life usage.

Well I'd say that using a PHP-CLI script to import bulk data is a
real-life usage and this is definitely a limiting factor. Do you
disagree?

On the contrary, for these kind of apps, garbage collecting systems
have potential to be significantly slower.

Well, Cocoa solves the problem in a manner I consider quite graceful.
In 99% of situations, you don't touch memory management and things
work themselves out like in PHP. However, there is a concept of a
WEAK REFERENCE (a non-ref-counted ptr to the object) that is used
specifically in these cases to prevent circular references.

With this type of system, there is no additional overhead because the
GC doesn't have to "detect" circular references and determine if the
objects are orphaned but deadlocked... instead this is a situation
left to the developer to manage.

Now I understand that PHP isn't Obj-C and it's a higher-level
language and that's fine.

However, my question, which still remains unanswered, is that I've
found a way that "seems" to create a weak reference and I'm simply
asking if what I am doing is condoned or just lucky (and thus a bad
idea that will probably break in the future)...

And, if it's just lucky, then what is the solution to the problem? Am
I just SOL? Is the answer simply that if you need to create
circular references in PHP, then you must accept memory leakage?

Alan

19 years ago by Robert Cummings — view source

unread

And, if it's just lucky, then what is the solution to the problem? Am
I just SOL? Is the answer simply that if you need to create
circular references in PHP, then you must accept memory leakage?

If you know you have a circular reference you can always use unset() to
break the reference and thus break the circle.

Cheers,
Rob.

.------------------------------------------------------------.
| InterJinn Application Framework - http://www.interjinn.com |
:------------------------------------------------------------:
| An application and templating framework for PHP. Boasting |
| a powerful, scalable system for accessing system services |
| such as forms, properties, sessions, and caches. InterJinn |
| also provides an extremely flexible architecture for |
| creating re-usable components quickly and easily. |
`------------------------------------------------------------'

19 years ago by Wez Furlong — view source

unread

However, my question, which still remains unanswered, is that I've
found a way that "seems" to create a weak reference and I'm simply
asking if what I am doing is condoned or just lucky (and thus a bad
idea that will probably break in the future)...

The general rule of thumb is that if what you're doing makes you feel
dirty inside, or feels wrong, or that it might not work in the future,
then you shouldn't rely on it working that way.

I'm not saying that this hack is or is not planned to go away, but there
is a real possibility that it might go away as the side-effect of some other
change.

So, if it works for you, that's fine... but if you're writing something that you
want to be used successfully with future PHP versions, then you should avoid
using it.

And, if it's just lucky, then what is the solution to the problem? Am
I just SOL? Is the answer simply that if you need to create
circular references in PHP, then you must accept memory leakage?

While I love the idea of writing everything in PHP, if you find
yourself up against
a limitation that you can't avoid without nasty hacks, then perhaps PHP
is the wrong tool for that particular job.

--Wez.

19 years ago by Jochem Maas — view source

unread

Andi - your email client seems to be leaking :-)

Andi Gutmans wrote:

Hi Alan,

Generally speaking, if you create a circular reference (whether by
reference or by value), then you will have a "memory leak" until the end
of the request. This is not only true for objects (and circular
references might be indirect) but also for arrays.
This is a side-effect of reference counting systems, but within the way
PHP is used within a request/response paradigm, it shouldn't be a real
limiting factor in real-life usage. On the contrary, for these kind of
apps, garbage collecting systems have potential to be significantly slower.

Andi

At 08:15 PM 12/7/2005, Alan Pinstein wrote:

My question is closely related to the one discussed on this php-dev
thread:

http://thread.gmane.org/gmane.comp.php.devel/32430

Someone just sent me this link, which I didn't find myself when
searching b/c the searches strip "this" from queries.

Anyway, the question is related to reference counting of objects when
assigned by value and by reference. It is a very important OO topic
as the ability to have a non-ref-counted object "handle" is basically
requisite to prevent circular reference deadlocks in OO projects.

If the way I have proposed doesn't work, then what is the official
way? And there must be one, otherwise, there is no way to avoid
huge memory leaks (deferred release until end-of-script, I know, but
it's a memory leak in the context of the script while it's running)
with this kind of OO arrangement.

In particular what confuses me is, why does, at least on PHP 5.0.4,
this:

$obj = &$this->this; // doesn't seem to increment the refcount of the
object

behaves differently from:

$obj = &$this; // does seem to increment the refcount to the
object

References to $this should not only be valid, but are pretty much
required for proper memory management in an OO environment, unless
there is some other sanctioned way to get a weak reference... now I
am not sure if the fact that making a & reference to an object
doesn't increment the refcount is intended behavior, or an unintended
side effect that may change. This is one of my major questions.

Also, in regards to the thread linked above, I'd say that making &
$this an error is not desirable behavior; but maybe changing the
value of $this should be (ie in C terms, $this is not an lvalue).
Although, in C++/Obj-C you can even change this/self... in fact
it's common in Obj-C:

(id) init
{
if (self = [super init]) { /* etc */ }
return self;
}

Of course PHP is not Obj-C, but it's OO and garbage collected in a
similar way, so PHP has the same need for manipulating $this; that
is, creating weak references.

Alan

Hi all-

<skip>
Please use php-general@lists.php.net for questions regarding
development in PHP.

Wbr, Antony Dovgal

19 years ago by Andi Gutmans — view source

unread

Sorry about that. I think it might be a problem with the server not my client.
If it persists please let me know.

At 08:37 AM 12/9/2005, Jochem Maas wrote:

Andi - your email client seems to be leaking :-)

Andi Gutmans wrote:

Hi Alan,
Generally speaking, if you create a circular reference (whether by
reference or by value), then you will have a "memory leak" until
the end of the request. This is not only true for objects (and
circular references might be indirect) but also for arrays.
This is a side-effect of reference counting systems, but within the
way PHP is used within a request/response paradigm, it shouldn't be
a real limiting factor in real-life usage. On the contrary, for
these kind of apps, garbage collecting systems have potential to be
significantly slower.
Andi
At 08:15 PM 12/7/2005, Alan Pinstein wrote:

My question is closely related to the one discussed on this php-dev
thread:

http://thread.gmane.org/gmane.comp.php.devel/32430

Someone just sent me this link, which I didn't find myself when
searching b/c the searches strip "this" from queries.

Anyway, the question is related to reference counting of objects when
assigned by value and by reference. It is a very important OO topic
as the ability to have a non-ref-counted object "handle" is basically
requisite to prevent circular reference deadlocks in OO projects.

If the way I have proposed doesn't work, then what is the official
way? And there must be one, otherwise, there is no way to avoid
huge memory leaks (deferred release until end-of-script, I know, but
it's a memory leak in the context of the script while it's running)
with this kind of OO arrangement.

In particular what confuses me is, why does, at least on PHP 5.0.4,
this:

$obj = &$this->this; // doesn't seem to increment the refcount of the
object

behaves differently from:

$obj = &$this; // does seem to increment the refcount to the object

References to $this should not only be valid, but are pretty much
required for proper memory management in an OO environment, unless
there is some other sanctioned way to get a weak reference... now I
am not sure if the fact that making a & reference to an object
doesn't increment the refcount is intended behavior, or an unintended
side effect that may change. This is one of my major questions.

Also, in regards to the thread linked above, I'd say that making &
$this an error is not desirable behavior; but maybe changing the
value of $this should be (ie in C terms, $this is not an lvalue).
Although, in C++/Obj-C you can even change this/self... in fact
it's common in Obj-C:

(id) init
{
if (self = [super init]) { /* etc */ }
return self;
}

Of course PHP is not Obj-C, but it's OO and garbage collected in a
similar way, so PHP has the same need for manipulating $this; that
is, creating weak references.

Alan

Hi all-

<skip>
Please use php-general@lists.php.net for questions regarding
development in PHP.

Wbr, Antony Dovgal

19 years ago by Jochem Maas — view source

unread

Andi Gutmans wrote:

Sorry about that. I think it might be a problem with the server not my
client.
If it persists please let me know.

given what your work has done for me I can't consider it a
problem :-) just thought it was kinda funny.

regarding the actually topic of this thread I'm very interested
in the concept of 'weak references' (as Apple seems to call them),
what '$this->this' is all about, and whether using reference notation
with object variable assignment is even allowed, whether it it makes
a difference and what the future holds with regard to being able to
use/create references to object 'handles'.

I remember someone else asking on this list about the ability/possiblity
of being able to make the distinction between object 'handles' and references
to object 'handles' - I can't remember anythnig conclusive coming out of
the discussion.

regardless I feel that Alan did make some valid points in this area,
given that the core/dev team may think that Alan's app (in this case) would
be better off being refactored it might be an idea for some documentation
to be created that gives an indication on how to overcome these percieved
referencing problems (i.e. some strategies on how to design something
that does work with in the confines of php's capabilities)

for the record I have an OO based import script that imports about 13
files, one of which has 500,000 lines of data, and I see that the memory usage
of my script grows and grows (upto about 100Mb) - I figure it could do it
alot more efficiently, having some ammunition regarding how to tackle
such an issue (in general terms) would be a great benefit - given the
generic nature of the problem I believe many more developers could benefit.

kind rgds,
Jochem

At 08:37 AM 12/9/2005, Jochem Maas wrote:

Andi - your email client seems to be leaking :-)

Andi Gutmans wrote:

Hi Alan,
Generally speaking, if you create a circular reference (whether by
reference or by value), then you will have a "memory leak" until the
end of the request. This is not only true for objects (and circular
references might be indirect) but also for arrays.
This is a side-effect of reference counting systems, but within the
way PHP is used within a request/response paradigm, it shouldn't be a
real limiting factor in real-life usage. On the contrary, for these
kind of apps, garbage collecting systems have potential to be
significantly slower.
Andi
At 08:15 PM 12/7/2005, Alan Pinstein wrote:

My question is closely related to the one discussed on this php-dev
thread:

http://thread.gmane.org/gmane.comp.php.devel/32430

Someone just sent me this link, which I didn't find myself when
searching b/c the searches strip "this" from queries.

Anyway, the question is related to reference counting of objects when
assigned by value and by reference. It is a very important OO topic
as the ability to have a non-ref-counted object "handle" is basically
requisite to prevent circular reference deadlocks in OO projects.

If the way I have proposed doesn't work, then what is the official
way? And there must be one, otherwise, there is no way to avoid
huge memory leaks (deferred release until end-of-script, I know, but
it's a memory leak in the context of the script while it's running)
with this kind of OO arrangement.

In particular what confuses me is, why does, at least on PHP 5.0.4,
this:

$obj = &$this->this; // doesn't seem to increment the refcount of
the
object

behaves differently from:

$obj = &$this; // does seem to increment the refcount to
the object

References to $this should not only be valid, but are pretty much
required for proper memory management in an OO environment, unless
there is some other sanctioned way to get a weak reference... now I
am not sure if the fact that making a & reference to an object
doesn't increment the refcount is intended behavior, or an unintended
side effect that may change. This is one of my major questions.

Also, in regards to the thread linked above, I'd say that making &
$this an error is not desirable behavior; but maybe changing the
value of $this should be (ie in C terms, $this is not an lvalue).
Although, in C++/Obj-C you can even change this/self... in fact
it's common in Obj-C:

(id) init
{
if (self = [super init]) { /* etc */ }
return self;
}

Of course PHP is not Obj-C, but it's OO and garbage collected in a
similar way, so PHP has the same need for manipulating $this; that
is, creating weak references.

Alan

Hi all-

<skip>
Please use php-general@lists.php.net for questions regarding
development in PHP.

Wbr, Antony Dovgal

19 years ago by Alan Pinstein — view source

unread

regarding the actually topic of this thread I'm very interested
in the concept of 'weak references' (as Apple seems to call them),
what '$this->this' is all about, and whether using reference notation
with object variable assignment is even allowed, whether it it makes
a difference and what the future holds with regard to being able to
use/create references to object 'handles'.

Yes, back to the thread :)

So a colleague on the propel-dev list has convinced me that my
approach is bad, mostly because of how references behave in PHP.
While doing my "research" I stumbled on to the fact that making
references doesn't bump refcounts, and got so excited by the
potential "solution" to my problem that I forgot about the flip-side
of using references, which is that it binds the reference to the same
place as the original. Thus, when the original changes, it changes
the target of your "stored link". So my solution in the end won't
work at all.

However, the need is definitely still there.

Andi briefly mentioned an alternative solution, and I am eagerly
awaiting his complete response... c'mon with it Andi!

Another poster recommended that maybe PHP isn't the right "tool" for
the job [of importing data]. This would imply that PHP is for your
web pages, but no other part of your application. Well, if I am
starting out on a new project, I'd like for the entire project to be
in one language. I want to be able to have all of my business logic
for my application's model in one place, and be able to use this core
model from the web, scripts, etc.

This poster's comment would indicate that PHP's stated purpose is as
a web tool only, and isn't intended as a project (now or in the
future) to be a universal solution to building applications. If this
is the case, I'd consider it a shame, and it would have me seriously
reconsider using PHP long term. A mindset like this is why there is
such anti-php sentiment from the ruby and python people. Whether you
like it or not, PHP has become a complete language platform. I like
the PHP paradigm overall, but need to be able to have projects
entirely in PHP for it to be worthwhile to use. If I have to develop
my core model in Java [or whatever], I am not sure that I would use
PHP to do the front-end.

Although, on a side note, I did recently use the excellent php-java-
bridge to build a PHP front-end to a Java search engine, and it works
very well. Not sure yet about performance, though.

Alan

19 years ago by dz@bitxtender.com — view source

unread

Would you mind explaining that "indirect property accessing" method,
Andi? Or did you mean avoiding circular references altogether by
having a third "intermediate" layer that would return the respective
object when handed a GUID or something, so that effectively, one of
the partners in the circle doesn't store the other partner directly,
but just a unique identifier usind which you can retrieve it? (that's
the way you have to do it in JavaScript if you don't want IE to crash
due to memleaks when referencing from DOM elements to JS objects and
vice versa)

Thanks,

David

Am 09.12.2005 um 18:08 schrieb Andi Gutmans:

Sorry about that. I think it might be a problem with the server not
my client.
If it persists please let me know.

At 08:37 AM 12/9/2005, Jochem Maas wrote:

Andi - your email client seems to be leaking :-)

Andi Gutmans wrote:

Hi Alan,
Generally speaking, if you create a circular reference (whether
by reference or by value), then you will have a "memory leak"
until the end of the request. This is not only true for objects
(and circular references might be indirect) but also for arrays.
This is a side-effect of reference counting systems, but within
the way PHP is used within a request/response paradigm, it
shouldn't be a real limiting factor in real-life usage. On the
contrary, for these kind of apps, garbage collecting systems have
potential to be significantly slower.
Andi
At 08:15 PM 12/7/2005, Alan Pinstein wrote:

My question is closely related to the one discussed on this php-dev
thread:

http://thread.gmane.org/gmane.comp.php.devel/32430

Someone just sent me this link, which I didn't find myself when
searching b/c the searches strip "this" from queries.

Anyway, the question is related to reference counting of objects
when
assigned by value and by reference. It is a very important OO topic
as the ability to have a non-ref-counted object "handle" is
basically
requisite to prevent circular reference deadlocks in OO projects.

If the way I have proposed doesn't work, then what is the official
way? And there must be one, otherwise, there is no way to avoid
huge memory leaks (deferred release until end-of-script, I know,
but
it's a memory leak in the context of the script while it's running)
with this kind of OO arrangement.

In particular what confuses me is, why does, at least on PHP 5.0.4,
this:

$obj = &$this->this; // doesn't seem to increment the
refcount of the
object

behaves differently from:

$obj = &$this; // does seem to increment the refcount
to the object

References to $this should not only be valid, but are pretty much
required for proper memory management in an OO environment, unless
there is some other sanctioned way to get a weak reference... now I
am not sure if the fact that making a & reference to an object
doesn't increment the refcount is intended behavior, or an
unintended
side effect that may change. This is one of my major questions.

Also, in regards to the thread linked above, I'd say that making
& $this an error is not desirable behavior; but maybe changing the
value of $this should be (ie in C terms, $this is not an lvalue).
Although, in C++/Obj-C you can even change this/self... in fact
it's common in Obj-C:

(id) init
{
if (self = [super init]) { /* etc */ }
return self;
}

Of course PHP is not Obj-C, but it's OO and garbage collected in a
similar way, so PHP has the same need for manipulating $this; that
is, creating weak references.

Alan

Hi all-

<skip>
Please use php-general@lists.php.net for questions regarding
development in PHP.

Wbr, Antony Dovgal

19 years ago by Alan Pinstein — view source

unread

Heh no problem. I'll cc the list for you.

So basically propel creates an object to represent each table in a
DB. Foreign key relationships are maintained, and the propel objects
cache the results.

So, in a simple scenario with "Account" and "Transactions", your
"Account" object keeps an internal "collection" of transactions and
each "transaction" keeps an internal reference to its "Account".
There's the circular reference.

So, if you could explain your idea (a) as a solution to this
architecture, that'd be great.

Also, why don't you describe (b) anyway just for fun :)

Alan

Not cc:'ing internals@ because for some reason it doesn't seem to
like me today (problem with our mail queue and lists.php.net)
Well I didn't have an exact solution in mind because I don't know
the exact problem you have and how you'd like to solve it. I was
thinking of two ways:
a) Doing some kind of id to object mapping (possibly using
overloading __get/__set).
b) Come to think of it, my (b), indirect references, isn't a good
idea :)

Andi

At 10:24 AM 12/9/2005, David Zülke wrote:

Would you mind explaining that "indirect property accessing" method,
Andi? Or did you mean avoiding circular references altogether by
having a third "intermediate" layer that would return the respective
object when handed a GUID or something, so that effectively, one of
the partners in the circle doesn't store the other partner directly,
but just a unique identifier usind which you can retrieve it? (that's
the way you have to do it in JavaScript if you don't want IE to crash
due to memleaks when referencing from DOM elements to JS objects and
vice versa)

Thanks,

David

Am 09.12.2005 um 18:08 schrieb Andi Gutmans:

Sorry about that. I think it might be a problem with the server not
my client.
If it persists please let me know.

At 08:37 AM 12/9/2005, Jochem Maas wrote:

Andi - your email client seems to be leaking :-)

Andi Gutmans wrote:

Hi Alan,
Generally speaking, if you create a circular reference (whether
by reference or by value), then you will have a "memory leak"
until the end of the request. This is not only true for objects
(and circular references might be indirect) but also for arrays.
This is a side-effect of reference counting systems, but within
the way PHP is used within a request/response paradigm, it
shouldn't be a real limiting factor in real-life usage. On the
contrary, for these kind of apps, garbage collecting systems have
potential to be significantly slower.
Andi
At 08:15 PM 12/7/2005, Alan Pinstein wrote:

My question is closely related to the one discussed on this
php-dev
thread:

http://thread.gmane.org/gmane.comp.php.devel/32430

Someone just sent me this link, which I didn't find myself when
searching b/c the searches strip "this" from queries.

Anyway, the question is related to reference counting of objects
when
assigned by value and by reference. It is a very important OO
topic
as the ability to have a non-ref-counted object "handle" is
basically
requisite to prevent circular reference deadlocks in OO projects.

If the way I have proposed doesn't work, then what is the
official
way? And there must be one, otherwise, there is no way to avoid
huge memory leaks (deferred release until end-of-script, I know,
but
it's a memory leak in the context of the script while it's
running)
with this kind of OO arrangement.

In particular what confuses me is, why does, at least on PHP
5.0.4,
this:

$obj = &$this->this; // doesn't seem to increment the
refcount of the
object

behaves differently from:

$obj = &$this; // does seem to increment the refcount
to the object

References to $this should not only be valid, but are pretty much
required for proper memory management in an OO environment,
unless
there is some other sanctioned way to get a weak reference...
now I
am not sure if the fact that making a & reference to an object
doesn't increment the refcount is intended behavior, or an
unintended
side effect that may change. This is one of my major questions.

Also, in regards to the thread linked above, I'd say that making
& $this an error is not desirable behavior; but maybe changing
the
value of $this should be (ie in C terms, $this is not an lvalue).
Although, in C++/Obj-C you can even change this/self... in fact
it's common in Obj-C:

(id) init
{
if (self = [super init]) { /* etc */ }
return self;
}

Of course PHP is not Obj-C, but it's OO and garbage collected
in a
similar way, so PHP has the same need for manipulating $this;
that
is, creating weak references.

Alan

Hi all-

<skip>
Please use php-general@lists.php.net for questions regarding
development in PHP.

Wbr, Antony Dovgal

$this->this and avoiding circular references

Please use php-general@lists.php.net for questions regarding development in PHP.

Please use php-general@lists.php.net for questions regarding development in PHP.

Please use php-general@lists.php.net for questions regarding development in PHP.

Please use php-general@lists.php.net for questions regarding development in PHP.

Cheers, Rob.

Please use php-general@lists.php.net for questions regarding development in PHP.

Please use php-general@lists.php.net for questions regarding development in PHP.

Please use php-general@lists.php.net for questions regarding development in PHP.

Please use php-general@lists.php.net for questions regarding development in PHP.

Please use php-general@lists.php.net for questions regarding development in PHP.

Please use php-general@lists.php.net for questions regarding
development in PHP.

Please use php-general@lists.php.net for questions regarding
development in PHP.

Please use php-general@lists.php.net for questions regarding
development in PHP.

Please use php-general@lists.php.net for questions regarding
development in PHP.

Cheers,
Rob.

Please use php-general@lists.php.net for questions regarding
development in PHP.

Please use php-general@lists.php.net for questions regarding
development in PHP.

Please use php-general@lists.php.net for questions regarding
development in PHP.

Please use php-general@lists.php.net for questions regarding
development in PHP.

Please use php-general@lists.php.net for questions regarding
development in PHP.