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Re: php daemon [message #179595 is a reply to message #179594]

Sun, 11 November 2012 21:36

Jerry Stuckle
Messages: 2598
Registered: September 2010

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Senior Member

On 11/11/2012 4:22 PM, Christoph Becker wrote:
> Jerry Stuckle wrote:
>> On 11/11/2012 3:05 PM, Christoph Becker wrote:
>>> Jerry Stuckle wrote:
>>>> All you can do is unset() variables. However, this does not release
>>>> memory immediately. It would wait for the garbage collector to run.
>>>
>>> I'm very much surprised. I /assumed/ that PHP uses reference counting,
>>> which would typically release the allocated memory as soon as the
>>> reference count of a value is 0.
>>>
>>
>> It does. But memory is not released until the garbage collector is run.
>> See the PHP documentation.
>
> Thanks for the pointer to the PHP documentation. According to
> <http://php.net/manual/en/features.gc.refcounting-basics.php>:
>
> | A PHP variable is stored in a container called a "zval". A zval
> | container contains, besides the variable's type and value, two
> | additional bits of information.
> | [...]
> | Variable containers get destroyed when the "refcount" reaches zero.
> | [...]
> | Again, when the "refcount" reaches zero, the variable container is
> | removed from memory.
>
> As this simple reference counting garbage collection isn't able to free
> circular structures, a garbage collector [1] to do so was introduced in
> PHP 5.3. Unfortunately the documentation isn't particularly clear here:
>
> | If the refcount is decreased and hits zero, the zval can be freed.
>
> But from the subsequent documentation I conclude, that the zval is
> actually freed, when the refcount is decreased to zero.
>
> [1] <http://www.php.net/manual/en/features.gc.collecting-cycles.php
>

No, that is the purpose of the garbage collector - which runs
occasionally at times determined by the php.ini file.

Notice the documentation says the zval CAN be freed - not the zval WILL
be freed. Two entirely different statements.

This is for performance reasons. It is much more to the running script
efficient to free a group of unused pieces of memory asynchronously than
to free the memory synchronously (every time the refcount goes to zero).

Note that PHP is not the only language to do it this way. Java does
also, for instance.

--
==================
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Jerry Stuckle
JDS Computer Training Corp.
jstucklex(at)attglobal(dot)net
==================

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[Message index]

		php daemon By: SL on Sun, 11 November 2012 17:18
		Re: php daemon By: Jerry Stuckle on Sun, 11 November 2012 19:04
		Re: php daemon By: Christoph Becker on Sun, 11 November 2012 20:05
		Re: php daemon By: Jerry Stuckle on Sun, 11 November 2012 20:35
		Re: php daemon By: Christoph Becker on Sun, 11 November 2012 21:22
		Re: php daemon By: Jerry Stuckle on Sun, 11 November 2012 21:36
		Re: php daemon By: Christoph Becker on Sun, 11 November 2012 22:17
		Re: php daemon By: Jerry Stuckle on Sun, 11 November 2012 23:11
		Re: php daemon By: Christoph Becker on Mon, 12 November 2012 13:35
		Re: php daemon By: Jerry Stuckle on Mon, 12 November 2012 13:38
		Re: php daemon By: Jerry Stuckle on Tue, 13 November 2012 12:44
		Re: php daemon By: Christoph Becker on Wed, 14 November 2012 20:19
		Re: php daemon By: Jerry Stuckle on Wed, 14 November 2012 21:33
		Re: php daemon By: Christoph Becker on Wed, 14 November 2012 22:13
		Re: php daemon By: Jerry Stuckle on Thu, 15 November 2012 12:41
		Re: php daemon By: Christoph Becker on Thu, 15 November 2012 15:55
		Re: php daemon By: SL on Mon, 12 November 2012 15:45
		Re: php daemon By: The Natural Philosoph on Mon, 12 November 2012 16:08
		Re: php daemon By: Goran on Tue, 13 November 2012 07:57
		Re: php daemon By: Jerry Stuckle on Tue, 13 November 2012 12:47
		Re: php daemon By: Goran on Tue, 13 November 2012 13:54
		Re: php daemon By: The Natural Philosoph on Tue, 13 November 2012 14:13
		Re: php daemon By: Jerry Stuckle on Tue, 13 November 2012 17:23
		Re: php daemon By: Goran on Wed, 14 November 2012 07:43
		Re: php daemon By: Jerry Stuckle on Wed, 14 November 2012 10:51
		Re: php daemon By: Goran on Thu, 15 November 2012 13:08
		Re: php daemon By: Jerry Stuckle on Thu, 15 November 2012 13:46
		Re: php daemon By: Goran on Thu, 15 November 2012 15:09
		Re: php daemon By: Jerry Stuckle on Thu, 15 November 2012 16:25
		Re: php daemon By: Tim Streater on Thu, 15 November 2012 16:20

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