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Date: Mon, 9 Jan 2006 13:57:32 -0500
To: Tim Starling <t.starling@physics.unimelb.edu.au>
Subject: Re: [PHP-DEV] 16-bit reference count in PHP 4's zval
From: apinstein@mac.com (Alan Pinstein)

It seems that the problem you're encountering could be fixed  
trivially by moving the initialization of $stuff into the constructor.

However, it's difficult to tell from the provided code whether $stuff  
is intended as a static member...  but if it's not, seems like a very  
simple fix...

I don't personally know about PHP4 internals, but it would seem that  
the reason it breaks as-is is that ALL CacheEntry objects initially  
report to the same (statically created) empty array. So, moving it  
into the constructor would at least create n empty arrays rather than  
segfaulting.

Right? Then you wouldn't even need to change your runtime environment  
(ie PHP version) to solve the problem.

Alan

On Jan 8, 2006, at 5:00 PM, Tim Starling wrote:

> Zeev Suraski wrote:
>> Tim,
>>
>> Your analysis was correct until the last sentence - PHP surely does
>> support arrays with more than 64K entries.  It just doesn't  
>> support the
>> same entry being linked from more than 64K locations (which is much,
>> much more rare occurrence).
>
> Well yes, I was just stirring. It's more common than you might  
> think though.
> My own case was somewhat similar to this:
>
> <?
> class CacheEntry {
>         var $name;
>         var $stuff = array();
>
>         function CacheEntry( $name ) {
>                 $this->name = $name;
>         }
> }
>
> $cache = array();
> for ( $i=0; $i<100000; $i++) {
>         $cache[] = new CacheEntry( "Cache entry $i" );
> }
> ?>
>
> ...which will segfault on exit due to the excess references to the  
> empty
> array object created for the initialisation of the unused member  
> variable
> $stuff. Generally speaking, arrays of objects with initialised but  
> unused
> member variables will cause problems. Our code (MediaWiki) has  
> plenty of
> such arrays, the reason we don't see this more often is because the  
> arrays
> usually contain less than 64K entries. The size of the arrays  
> depend on user
> input.
>
> -- Tim Starling
>
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