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Bug #79822 Opcache and get_class_vars() - first output correct, subsequent outputs wrong
Submitted: 2020-07-09 13:42 UTC Modified: 2020-07-13 08:20 UTC
From: wadih at systemesmw dot com Assigned:
Status: Verified Package: opcache
PHP Version: 7.4.3 OS: Ubuntu
Private report: No CVE-ID: None
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From: wadih at systemesmw dot com
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 [2020-07-09 13:42 UTC] wadih at systemesmw dot com
Description:
------------
The same call to get_class_vars() prints different values depending if it's the first time I run it, or if it's subsequent times, when opcache is on which is on by default. (See code in Test script)

First time, e.g. http://localhost/mytest.php, it prints:

7.4.3
Array
(
    [v] => a
)
Array
(
    [v] => b
)

Refresh the page, now prints:

7.4.3
Array
(
    [v] => a
)
Array
(
    [v] => a
)

Any subsequent refreshes prints [v] => a

Now slightly modify the PHP page to trigger a change , and it prints:

7.4.3
Array
(
    [v] => a
)
Array
(
    [v] => b
)

Refresh the page, and goes back to:

7.4.3
Array
(
    [v] => a
)
Array
(
    [v] => a
)

And subsequent refreshes still print [v] => a

SOLUTION: 

Set opcache.enable=0 in php.ini, restart apache2. Bug disappears, and prints [v] => b each time now. 

VERSIONS:

Apache/2.4.41 (Ubuntu)
PHP 7.4.3 (cli)
libapache2-mod-php 2:7.4+75

Test script:
---------------
class MyClass {
    public static $v = 'a';
}

echo '<pre>';
echo phpversion() . "\n";
print_r(get_class_vars('MyClass'));
MyClass::$v = 'b';
print_r(get_class_vars('MyClass'));

Expected result:
----------------
7.4.3
Array
(
    [v] => a
)
Array
(
    [v] => b
)

Actual result:
--------------
7.4.3
Array
(
    [v] => a
)
Array
(
    [v] => a
)

// Note, it is correct only first time it is run, but wrong all subsequent times, when opcache is active

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 [2020-07-09 13:44 UTC] wadih at systemesmw dot com
-Summary: Opcache get_class_vars() - first run successful, subsequent runs wrong +Summary: Opcache and get_class_vars() - first output correct, subsequent outputs wrong -PHP Version: 7.4.7 +PHP Version: 7.4.3
 [2020-07-09 13:44 UTC] wadih at systemesmw dot com
update summary
 [2020-07-09 13:56 UTC] stsalkov at gmail dot com
Can confirm this on a vanilla Ubuntu 20.04LTS install (Apache/2.4.41, PHP 7.4.3).
 [2020-07-09 16:57 UTC] cmb@php.net
-Status: Open +Status: Verified
 [2020-07-09 16:57 UTC] cmb@php.net
With the most recent PHP-7.4 from Git, I get the wrong result on
CLI (Windows) with OPcache enabled right away on the first run.
This may have the same root cause as bug #79487.
 [2020-07-13 08:20 UTC] nikic@php.net
What is the expected behavior here? The docs say:

> Returns an associative array of declared properties visible from the current scope, with their default value. The resulting array elements are in the form of varname => value. In case of an error, it returns FALSE. 

So based on that, and what the implementation does, the intention here was to return the default values, not the current values. However, historically we don't even remember the default values of static properties! In 7.4 we do if opcache is loaded, thus the change in behavior.

ReflectionClass::getDefaultProperties() is probably also affected.
 [2020-07-14 17:46 UTC] stsalkov at gmail dot com
Since this behavior dates back to PHP 4, I think it'd be fair to say "the documentation is wrong" rather than "the implementation is wrong." To me, the culture of not breaking backwards compatibility has always been an important part of PHP.

In any case, it shouldn't behave differently depending on whether opcache is enabled.
 
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