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Groups > comp.lang.php > #7526

Re: php daemon

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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.

-- 
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
==================

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php daemon "sl@exabyte" <sb5309@hotmail.com> - 2012-11-12 01:18 +0800
  Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-11 14:04 -0500
    Re: php daemon Christoph Becker <cmbecker69@gmx.de> - 2012-11-11 21:05 +0100
      Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-11 15:35 -0500
        Re: php daemon Christoph Becker <cmbecker69@gmx.de> - 2012-11-11 22:22 +0100
          Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-11 16:36 -0500
            Re: php daemon Christoph Becker <cmbecker69@gmx.de> - 2012-11-11 23:17 +0100
              Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-11 18:11 -0500
                Re: php daemon Christoph Becker <cmbecker69@gmx.de> - 2012-11-12 14:35 +0100
                Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-12 08:38 -0500
                Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-13 07:44 -0500
                Re: php daemon Christoph Becker <cmbecker69@gmx.de> - 2012-11-14 21:19 +0100
                Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-14 16:33 -0500
                Re: php daemon Christoph Becker <cmbecker69@gmx.de> - 2012-11-14 23:13 +0100
                Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-15 07:41 -0500
                Re: php daemon Christoph Becker <cmbecker69@gmx.de> - 2012-11-15 16:55 +0100
    Re: php daemon "sl@exabyte" <sb5309@hotmail.com> - 2012-11-12 23:45 +0800
      Re: php daemon The Natural Philosopher <tnp@invalid.invalid> - 2012-11-12 16:08 +0000
  Re: php daemon Goran <goran@nospam.com> - 2012-11-13 08:57 +0100
    Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-13 07:47 -0500
      Re: php daemon Goran <goran@nospam.com> - 2012-11-13 14:54 +0100
        Re: php daemon The Natural Philosopher <tnp@invalid.invalid> - 2012-11-13 14:13 +0000
        Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-13 12:23 -0500
          Re: php daemon Goran <goran@nospam.com> - 2012-11-14 08:43 +0100
            Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-14 05:51 -0500
              Re: php daemon Goran <goran@nospam.com> - 2012-11-15 14:08 +0100
                Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-15 08:46 -0500
                Re: php daemon Goran <goran@nospam.com> - 2012-11-15 16:09 +0100
                Re: php daemon Jerry Stuckle <jstucklex@attglobal.net> - 2012-11-15 11:25 -0500
                Re: php daemon Tim Streater <timstreater@greenbee.net> - 2012-11-15 16:20 +0000

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