imagedestroy and similar

[=?iso-8859-1?B?QW5kcukgSORuc2Vs?=]

Hi,

is there a difference between imagedestroy($i h) and unset($ih)?

The same with other similar functions like closedir, mysql_close,
curl_close, mysql_free_resu lt, etc.

And by the way... will the garbage collector even detect an "implicit
unset" when a resource is used for the last time?

Regards,
André

[Jerry Stuckle]

Re: imagedestroy and similar

ljb wrote:

andre@webkr.de wrote:

>Hi,
>>
>is there a difference between imagedestroy($i h) and unset($ih)?
>>
>The same with other similar functions like closedir, mysql_close,
>curl_close, mysql_free_resu lt, etc.
>>
>And by the way... will the garbage collector even detect an "implicit
>unset" when a resource is used for the last time?

>
In the case of GD, I think imagedestroy does nothing more than unset. But
you probably should not assume that in general. If the resource is properly
implemented, then yes unsetting it should do all the necessary cleanup.
>
The garbage collector does not detect when a resource is used for the last
time. It does detect when it goes out of scope. For example, a resource
variable local to a function ... when the function returns, the resource
should be cleaned up.

One correction - the gc eventually detects when the resource is no
longer being used. But such detection is almost always not immediate,
and may in fact take quite some time.

It's much better to destroy the resources when you're done with them and
not leave it up to the gc. Doing the latter is just plain sloppy, lazy
or both.

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[gosha bine]

Re: imagedestroy and similar

On 20.04.2007 02:17 André Hänsel wrote:

Hi,
>
is there a difference between imagedestroy($i h) and unset($ih)?

No. unset() checks if a variable is referenced elsewhere and if not,
destroys the variable and its value immediately. This is called
"reference counting".

>
The same with other similar functions like closedir, mysql_close,
curl_close, mysql_free_resu lt, etc.

Yes, if an extension author took care of registering his destructor in
zend core.

>
And by the way... will the garbage collector even detect an "implicit
unset" when a resource is used for the last time?

php doesn't use "garbage collector", memory is reclaimed immediately as
it becomes inaccesible.

>
Regards,
André
>

--
gosha bine

extended php parser ~ http://code.google.com/p/pihipi
blok ~ http://www.tagarga.com/blok

[Jerry Stuckle]

Re: imagedestroy and similar

gosha bine wrote:

On 20.04.2007 02:17 André Hänsel wrote:

>Hi,
>>
>is there a difference between imagedestroy($i h) and unset($ih)?

>
No. unset() checks if a variable is referenced elsewhere and if not,
destroys the variable and its value immediately. This is called
"reference counting".
>

>>
>The same with other similar functions like closedir, mysql_close,
>curl_close, mysql_free_resu lt, etc.

>
Yes, if an extension author took care of registering his destructor in
zend core.
>

>>
>And by the way... will the garbage collector even detect an "implicit
>unset" when a resource is used for the last time?

>
php doesn't use "garbage collector", memory is reclaimed immediately as
it becomes inaccesible.
>

>>
>Regards,
>André
>>

>
>

Andre,

Not completely true.

Yes, memory is reclaimed immediately when you unset the resource. But if
you don't unset it before the end of the page, there may be a delay
before PHP gets around to cleaning things up. It doesn't necessarily do
it immediately.

Also, there is a garbage collector for sessions to clean up old session
files. But that's different.


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Remove the "x" from my email address
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jstucklex@attgl obal.net
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[Jerry Stuckle]

Re: imagedestroy and similar

ljb wrote:

jstucklex@attgl obal.net wrote:

>ljb wrote:

>>>...
>>The garbage collector does not detect when a resource is used for the last
>>time. It does detect when it goes out of scope. For example, a resource
>>variable local to a function ... when the function returns, the resource
>>should be cleaned up.

>One correction - the gc eventually detects when the resource is no
>longer being used. But such detection is almost always not immediate,
>and may in fact take quite some time.

>
Just for discussion, is there a case where PHP can "detect when the
resource is no longer being used" other than when the variable referencing
the resource goes out of scope? I believe you that there is, but I can't
think of any.
>
Also are you saying that if the resource is a local variable in a function,
and the function returns, there can be a delay before the resource is
cleaned up (for example, a database connection is closed)?

I was referring specifically to when the page completes. Cleanup may
not be done immediately. I don't know for sure about when a function exits.

And no, there is no way for PHP to predict if a resource still being
referenced by a variable is going to be used or not. I'd love it if
they could - I'd use that to write a program to predict the lottery
numbers :-)


--
=============== ===
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