Opcache corruption

[vnsavage]

Description

The following code:

1. Clear PHP Opcache
2. Add files:

$ cat test.php 
<?php
include( 'test-class1.php' );
include( 'test-class2.php' );

$ cat test-class1.php 
<?php
class test_class {
	public static $a = true;
}

$ cat test-class2.php 
<?php
var_dump( test_class::$a );
class test_class {
	public static $a = true;
}

3. Issue a web request to test.php
4. Remove the include -> "include( 'test-class1.php' )" from test.php
5. Issue a second web request to test.php again

Resulted in this output:

First Request: Fatal error: Cannot declare class test_class, because the name is already in use in test-class2.php on line 5
Second Request: Fatal error: Uncaught Error: Class 'test_class' not found in test-class2.php:3 

But I expected this output instead:

First Request: Fatal error: Cannot declare class test_class, because the name is already in use in test-class2.php on line 5
Second request: bool(true)

PHP Version

PHP 8.0

Operating System

Linux

[cmb69]

Well, the problem is that on the first request, the test_class::$a in test-class2.php refers to test_class in test-class1.php. This reference is resolved, and stored in the op_array. On the second request, that test_class is no longer available, but OPcache doesn't automatically re-compile test-class2.php, so the error is raised. You can work around that by touching test-class2.php before doing the second request.

I think we should treat this as WONTFIX, since fixing this issue (and related issues) would make OPcache less efficient, and it seems to be a uncommon edge-case anyway.

[vnsavage]

It's very easy to reproduce with activating 2 different versions of a simple WordPress plugin twice, then realizing your error and deactivating one of the plugins. touching will probably fix it only if you 1) have opcache.validate_timestamps enabled and 2) also you know or are able to debug what the problem is. This is a very reduced test case that I posted but in practice it's not so obvious for most people what's happening.

[mvorisek]

It is a bug, opcache should work /wo any side effect. Class can be loaded from cache only if the containing file was required/included in the current request/preload.

[cmb69]

One may argue that the user should cater to such changes by calling opcache_reset().

[vnsavage]

It doesn't seem like this is how Opcache is supposed to work. If it were acceptable, which I don't think it is, that Opcache should be corrupted by certain user actions or have unexpected behavior, this should probably be well documented in a public visible document (e.g. https://www.php.net/opcache ) and all those cases described.

I don't think it's reasonable to expect a regular user or a developer or even a sys admin to be able to quickly see, diagnose and solve such a problem. Neither is calling opcache_reset() is a proper way to address any problem as it often causes more problems and is not scalable nor efficient. Also there are different environments you can consider, not only hosting your personal site, but it can also happen on places where you will not notice or resolve the problem quickly, like shared hosting services etc.

[IAMBANN]

Hi @vnsavage,
After issuing web request to test.php file including both the statements i.e. include( 'test-class1.php' ); and include( 'test-class2.php' ); it gives expected output with PHP v8.1

[vnsavage]

Hey @IAMBANN my tests show that it's still reproducible under PHP 8.1. Did you follow all the steps I listed, creating the exact same files and issuing 2 requests while modifying test.php between the 2 requests? Were you able to reproduce it with the earlier versions? Do you have opcache enabled?

[IAMBANN]

Hi @vnsavage,
Followed your steps and created the exact same files. After issuing web request to test.php, the expected output is still achieved while using PHP v7.4 and PHP v8.1 and also the opcache is enabled by following article.