[PHP] Reading class variable value always returns NULL
Hi,
So I have this strange situation where I assign a classvariable a
value, but when I read the value it is NULL.
The class has one variable declared:
=
class A {
private $_cookies;
}
=
In a method of this class I assign this classvariable plus an
undeclared classvariable and a local variable the value 1:
=
$this->_cookies = 1;
$this->_cookies2 = 1;
$cookies3 = 1;
=
When I now read the values of those variables, the classvariables are
NULL while the local variable is 1:
=
$logEntry .= 'cookies: ' . var_export($this->_cookies, true) . PHP_EOL;
$logEntry .= 'cookies2: ' . var_export($this->_cookies2, true) . PHP_EOL;
$logEntry .= 'cookies3: ' . var_export($cookies3, true) . PHP_EOL;
=
cookies: NULL
cookies2: NULL
cookies3: 1
=
But when reading the whole object, the classvariables are 1:
=
$logEntry .= var_export($this, true) . PHP_EOL;
=
A::__set_state(array(
'_cookies' => 1,
'_cookies2' => 1,
))
=
This happens periodically on a busy webserver. It seems that when it
happens, all classvariables cannot be read anymore (return NULL).
After restarting Apache it does not happen anymore, just to happen
again after some minutes.
The system is current Debian Squeeze:
Linux: linux-image-2.6.32-5-amd64
Apache: apache2-mpm-prefork 2.2.16-6+squeeze7
PHP: PHP 5.3.3-7+squeeze13 with Suhosin-Patch (cli) (built: Jun 10
2012 07:31:32)
php -m:
https://raw.github.com/gist/3331641/2f7e80bd03abfb728b659634d3f4bac0131f4d6a/gistfile1.txt
php -i:
https://raw.github.com/gist/3331651/bcf6e3654bf391482627505447848de173d0bbab/gistfile1.txt
Does anyone have an idea what could cause this, or how to further debug?
Thanks,
Reto
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Re: [PHP] Reading class variable value always returns NULL
Hi,
Thanks for your input Robert and Volmar! I have googled again with
"instance variable" instead of "class variable" - but have not found
any similar reports.
I'm pretty sure those are the same objects. The application usually
runs alright. We only see the instance variables becoming NULL since
about a week.
We had 3 small software upgrade coming from debian since we observe
the problem. We think they cannot be related. Still we have reverted
all of those and still see the problem.
Next step is that we setup a exact copy of the machine. Maybe it is a
hardware problem...
Thanks,
Reto
On Mon, Aug 13, 2012 at 5:09 PM, Robert Cummings wrote:
> On 12-08-12 08:32 AM, Reto Kaiser wrote:
>>
>> Hi,
>>
>> So I have this strange situation where I assign a classvariable a
>> value, but when I read the value it is NULL.
>>
>> The class has one variable declared:
>> =
>> class A {
>> private $_cookies;
>> }
>> =
>
>
> That is a private instance variable NOT a class variable.
>
> To declare a class variable you would do the following:
>
>
> class A
> {
> private static $_cookies;
> }
>
> ?>
>
>
>> In a method of this class I assign this classvariable plus an
>> undeclared classvariable and a local variable the value 1:
>> =
>> $this->_cookies = 1;
>> $this->_cookies2 = 1;
>> $cookies3 = 1;
>> =
>>
>> When I now read the values of those variables, the classvariables are
>> NULL while the local variable is 1:
>> =
>> $logEntry .= 'cookies: ' . var_export($this->_cookies, true) . PHP_EOL;
>> $logEntry .= 'cookies2: ' . var_export($this->_cookies2, true) . PHP_EOL;
>> $logEntry .= 'cookies3: ' . var_export($cookies3, true) . PHP_EOL;
>> =
>> cookies: NULL
>> cookies2: NULL
>> cookies3: 1
>> =
>>
>> But when reading the whole object, the classvariables are 1:
>> =
>> $logEntry .= var_export($this, true) . PHP_EOL;
>> =
>> A::__set_state(array(
>> '_cookies' => 1,
>> '_cookies2' => 1,
>> ))
>> =
>>
>>
>> This happens periodically on a busy webserver. It seems that when it
>> happens, all classvariables cannot be read anymore (return NULL).
>> After restarting Apache it does not happen anymore, just to happen
>> again after some minutes.
>>
>> The system is current Debian Squeeze:
>> Linux: linux-image-2.6.32-5-amd64
>> Apache: apache2-mpm-prefork 2.2.16-6+squeeze7
>> PHP: PHP 5.3.3-7+squeeze13 with Suhosin-Patch (cli) (built: Jun 10
>> 2012 07:31:32)
>> php -m:
>> https://raw.github.com/gist/3331641/2f7e80bd03abfb728b659634d3f4bac0131f4d6a/gistfile1.txt
>> php -i:
>> https://raw.github.com/gist/3331651/bcf6e3654bf391482627505447848de173d0bbab/gistfile1.txt
>>
>> Does anyone have an idea what could cause this, or how to further debug?
>
>
> I can't really speak to your specific problem (unless you're using two
> different instances of the class), just thought I'd clear up the difference
> between class variables and instance variables.
>
> Cheers,
> Rob.
> --
> E-Mail Disclaimer: Information contained in this message and any
> attached documents is considered confidential and legally protected.
> This message is intended solely for the addressee(s). Disclosure,
> copying, and distribution are prohibited unless authorized.
--
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Re: [PHP] Reading class variable value always returns NULL
Hi,
We have since deployed another webserver machine and observe the exact
same behavior there.
So it is not a hardware problem.
We have also disabled various php modules, but this didn't help either.
Any debug suggestions are welcome! :)
Reto
On Tue, Aug 14, 2012 at 10:40 AM, Reto Kaiser wrote:
> Hi,
>
> Thanks for your input Robert and Volmar! I have googled again with
> "instance variable" instead of "class variable" - but have not found
> any similar reports.
>
> I'm pretty sure those are the same objects. The application usually
> runs alright. We only see the instance variables becoming NULL since
> about a week.
>
> We had 3 small software upgrade coming from debian since we observe
> the problem. We think they cannot be related. Still we have reverted
> all of those and still see the problem.
> Next step is that we setup a exact copy of the machine. Maybe it is a
> hardware problem...
>
> Thanks,
> Reto
>
> On Mon, Aug 13, 2012 at 5:09 PM, Robert Cummings wrote:
>> On 12-08-12 08:32 AM, Reto Kaiser wrote:
>>>
>>> Hi,
>>>
>>> So I have this strange situation where I assign a classvariable a
>>> value, but when I read the value it is NULL.
>>>
>>> The class has one variable declared:
>>> =
>>> class A {
>>> private $_cookies;
>>> }
>>> =
>>
>>
>> That is a private instance variable NOT a class variable.
>>
>> To declare a class variable you would do the following:
>>
>> >
>> class A
>> {
>> private static $_cookies;
>> }
>>
>> ?>
>>
>>
>>> In a method of this class I assign this classvariable plus an
>>> undeclared classvariable and a local variable the value 1:
>>> =
>>> $this->_cookies = 1;
>>> $this->_cookies2 = 1;
>>> $cookies3 = 1;
>>> =
>>>
>>> When I now read the values of those variables, the classvariables are
>>> NULL while the local variable is 1:
>>> =
>>> $logEntry .= 'cookies: ' . var_export($this->_cookies, true) . PHP_EOL;
>>> $logEntry .= 'cookies2: ' . var_export($this->_cookies2, true) . PHP_EOL;
>>> $logEntry .= 'cookies3: ' . var_export($cookies3, true) . PHP_EOL;
>>> =
>>> cookies: NULL
>>> cookies2: NULL
>>> cookies3: 1
>>> =
>>>
>>> But when reading the whole object, the classvariables are 1:
>>> =
>>> $logEntry .= var_export($this, true) . PHP_EOL;
>>> =
>>> A::__set_state(array(
>>> '_cookies' => 1,
>>> '_cookies2' => 1,
>>> ))
>>> =
>>>
>>>
>>> This happens periodically on a busy webserver. It seems that when it
>>> happens, all classvariables cannot be read anymore (return NULL).
>>> After restarting Apache it does not happen anymore, just to happen
>>> again after some minutes.
>>>
>>> The system is current Debian Squeeze:
>>> Linux: linux-image-2.6.32-5-amd64
>>> Apache: apache2-mpm-prefork 2.2.16-6+squeeze7
>>> PHP: PHP 5.3.3-7+squeeze13 with Suhosin-Patch (cli) (built: Jun 10
>>> 2012 07:31:32)
>>> php -m:
>>> https://raw.github.com/gist/3331641/2f7e80bd03abfb728b659634d3f4bac0131f4d6a/gistfile1.txt
>>> php -i:
>>> https://raw.github.com/gist/3331651/bcf6e3654bf391482627505447848de173d0bbab/gistfile1.txt
>>>
>>> Does anyone have an idea what could cause this, or how to further debug?
>>
>>
>> I can't really speak to your specific problem (unless you're using two
>> different instances of the class), just thought I'd clear up the difference
>> between class variables and instance variables.
>>
>> Cheers,
>> Rob.
>> --
>> E-Mail Disclaimer: Information contained in this message and any
>> attached documents is considered confidential and legally protected.
>> This message is intended solely for the addressee(s). Disclosure,
>> copying, and distribution are prohibited unless authorized.
--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP] Reading class variable value always returns NULL
Hey,
We have:
error_reporting((E_ALL | E_STRICT) & ~(E_NOTICE | E_USER_NOTICE));
Displaying errors is disabled:
display_errors = Off
We have a custom error handler which logs all errors to a file.
In this file we receive byeffect errors, like that the second argument
to "array_key_exists" should be array, but is NULL. When we further
debug the reason is that the second argument is an instance variable,
and all instance variables are NULL.
We're pretty sure this is a software bug, since it only happens from
time to time, and already happens in the first line of the php script,
when none of our application code was loaded.
For example:
foo = 1;
if ($a->foo === null) {
throw new Exception("strange");
}
will throw an exception.
Since it only happens from time to time, it is really hard to debug.
We're now trying to reproduce in a virtual machine environment, while
replaying the actual requests that our webserver received. When we're
just simulating random load on the web server it doesn't happen. So it
must have something to do with certain requests, and they must have
some strange byeffect on php, or mod_php or something related.
Any input welcome!
Thanks,
Reto
On Tue, Aug 14, 2012 at 11:11 PM, Jim Lucas wrote:
> On 08/12/2012 05:32 AM, Reto Kaiser wrote:
>>
>> Hi,
>>
>> So I have this strange situation where I assign a classvariable a
>> value, but when I read the value it is NULL.
>>
>> Does anyone have an idea what could cause this, or how to further debug?
>>
>> Thanks,
>> Reto
>>
>
> What is your error reporting set to?
>
> Do you have display errors turned on?
>
> Are you saving your errors to a log file?
>
> --
> Jim Lucas
>
> http://www.cmsws.com/
> http://www.cmsws.com/examples/
--
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Re: [PHP] Reading class variable value always returns NULL
So here's some new observations on the instance variables being NULL.
As far as we found out this is the sequence of events:
1. Apache (MPM) received request A which executes a php script.
2. Within this script during the unserialization of an object an
exception is thrown.
3. This exception is catched and an error message is display to
standard output with "echo".
4. The script ends normally and the standard output contents are
returned in the HTTP response.
5. From now on this Apache worker is "tainted", meaning that every
subsequent request will result in:
6. The same apache worker receives request B which executes a PHP script.
7. Within this PHP script reading instance variables will always
return NULL, e.g.:
foo = 1;
// Now: $a->foo === NULL
All subsequent requests to this apache worker will behave like this.
The constellation leading to this behavior is very hard to further
simplify. If we throw different exceptions, or unserialize different
objects it doesn't happen anymore...
As a workaround we added "exit;" to the end of our php script. With a
call to "exit" the apache worker will not get "tainted"...
Regards,
Reto
On Tue, Aug 14, 2012 at 11:52 PM, Reto Kaiser wrote:
> Hey,
>
> We have:
> error_reporting((E_ALL | E_STRICT) & ~(E_NOTICE | E_USER_NOTICE));
>
> Displaying errors is disabled:
> display_errors = Off
>
> We have a custom error handler which logs all errors to a file.
> In this file we receive byeffect errors, like that the second argument
> to "array_key_exists" should be array, but is NULL. When we further
> debug the reason is that the second argument is an instance variable,
> and all instance variables are NULL.
> We're pretty sure this is a software bug, since it only happens from
> time to time, and already happens in the first line of the php script,
> when none of our application code was loaded.
> For example:
>
> class A{}
> $a = new A();
> $a->foo = 1;
> if ($a->foo === null) {
> throw new Exception("strange");
> }
>
> will throw an exception.
>
> Since it only happens from time to time, it is really hard to debug.
> We're now trying to reproduce in a virtual machine environment, while
> replaying the actual requests that our webserver received. When we're
> just simulating random load on the web server it doesn't happen. So it
> must have something to do with certain requests, and they must have
> some strange byeffect on php, or mod_php or something related.
>
> Any input welcome!
>
> Thanks,
> Reto
>
> On Tue, Aug 14, 2012 at 11:11 PM, Jim Lucas wrote:
>> On 08/12/2012 05:32 AM, Reto Kaiser wrote:
>>>
>>> Hi,
>>>
>>> So I have this strange situation where I assign a classvariable a
>>> value, but when I read the value it is NULL.
>>>
>>> Does anyone have an idea what could cause this, or how to further debug?
>>>
>>> Thanks,
>>> Reto
>>>
>>
>> What is your error reporting set to?
>>
>> Do you have display errors turned on?
>>
>> Are you saving your errors to a log file?
>>
>> --
>> Jim Lucas
>>
>> http://www.cmsws.com/
>> http://www.cmsws.com/examples/
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