__PHP_Incomplete_Class_Name wrong

Question

We're randomly getting some very strange error logs. They don't happen on every page hit, even with the same parameters/actions/etc, and they don't seem repeatable, each one is different in its crash location, and context. But almost all have incorrect __PHP_Incomplete_Class_Name as the cause.

One such error is:

main(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "LoginLogging" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition

The problem being, there is no "LoginLogging" class. The object it's referring to was of type ScormElement when it was saved into the session. Doing a dump of the variable gives:

__PHP_Incomplete_Class::__set_state(array(
 '__PHP_Incomplete_Class_Name' => 'LoginLogging',
 'intUserId' => '64576',
 '__intUserId' => '64576',
 'intScormId' => '665',
 '__intScormId' => '665',
 'intScoId' => '9255',
 '__intScoId' => '9255',
 'strElement' => 'cmi.core.lesson_location',
 '__strElement' => 'cmi.core.lesson_location',
 'strValue' => '1',
 'dttTimeModified' => QDateTime::__set_state(array(
   'blnDateNull' => false,
   'blnTimeNull' => false,
   'strSerializedData' => '2011-08-31T08:05:22-0600',
   'date' => '2011-08-31 08:05:22',
   'timezone_type' => 1,
   'timezone' => '-06:00',
 )),
 '__strVirtualAttributeArray' => array (),
 '__blnRestored' => true,
 'objUser' => NULL,
 'objScorm' => NULL,
)

All the properties are retained correctly, and match the class definition for ScormElement. But the class name is wrong. There is no class named LoginLogging.

What is causing this and how do we fix it???

Edit: This is just an example. Other errors are very similar in structure, but affect other class types, and have different incomplete names. However, ALL incomplete names have the same string length of the correct class name.

Edit 2011-10-27: I'm still seeing these error logs, and have had no success in finding a solution. Any help would be appreciated.

PHP 5.3.3, APC, default session handler.

Answer 1

As written in the quote in your question __PHP_Incomplete_Class_Name is a special class name in PHP that is used whenever the class definition could not be found when unserializing (unserialize()).

It's suggested to either ensure the class definition is available or to provide some autoloading for the missing class.

You commented that PHP is looking for the wrong classname here:

wrong: LoginLogging
right: ScormElement

It's hard to say with the information given why the classname is being changed on serialization/unserialization. The information you've given (especially the dump) in your question is incomplete.

So the options are limited to some general suggestions:

You could inspect the serialized string which classname is given in there so you could at least say if it happens with serialization or unserialization. You can easily inspect serialized data with the Serialized PHP Library which has a text-dumper for debug purposes.

Additionally there is the unserialize_callback_func Ini-Directive you can use to further trace the problem.

<?php
$serialized_object='O:1:"a":1:{s:5:"value";s:3:"100";}';

// unserialize_callback_func directive available as of PHP 4.2.0
ini_set('unserialize_callback_func', 'mycallback'); // set your callback_function

function mycallback($classname) 
{
    // just include a file containing your classdefinition
    // you get $classname to figure out which classdefinition is required
}

As you write the problem does not occur any longer, I suspect that at some point the serialization on your site was broken storing invalid data. Which framework/libraries/application are you using? Which component takes care about serialization?