WP reverts to default theme on file access collision

[_ck_]

There is still no fix addressed to the problem on heavily accessed systems where the theme can revert back to default.

This apparently happens if the "file_exists" test in ​theme.php fails under any of a few different functions? PHP manual shows that "file_exists" can fail if a theme file is being replaced at the time or certain conditions occur under php safe mode.

One way to reproduce this bug consistently is to upload "style.css" repeatedly while a site is active.

I'd like to suggest that "file_exists" be replaced with a custom function that does at least a few retries over an adjustable time (a second or so) before completely giving up and reverting.

[_ck_]

Untested suggestion, some code borrowed from php.net

function wp_file_exists($file) {
$start = gettimeofday(); 
     while (!file_exists(trim($file, " '\""))) {
       $stop = gettimeofday();
       if ( 1000000 * ($stop['sec'] - $start['sec']) + stop['usec']   - $start['usec'] > 500000) {
           return file_exists(trim($file, " '\"")); }
     } 
return true;
}

[markjaquith]

Aha. I've heard of the symptom, but had no idea of the root cause. Thanks for the report.

Maybe we could do this:

1. read the active theme name from the options table
2. update the file
3. check the active theme name from the options table, and revert if it has changed since #1

[f00f]

markjaquith: What do you mean by 'update the file'?

The scenario (if I understood correctly) is as follows:

While you are uploading a new stylesheet (or other theme file) via FTP a user visits your site. Then file_exists() could fail because the file is actually opened by another process than the web server.

As a result the current theme gets permanently reset to 'default' in validate_current_theme().

IMHO, one second is to long for a timeout.

Another solution might be to check if the template folder exists and assume that index.php and style.css exist in it.

[Denis-de-Bernardy]

Could we get this into 2.3? I've seen this happen a couple times, and it's rather annoying when it comes up. Changing the code to check for the template folder would work imho, and the change is rather trivial.

D.

[foolswisdom]

Without a patch attached no. Without testing of the solution, no.

Moving to milestone 2.5 pending a tested patch.

[markjaquith]

I've had more reports of this happening.

I like the idea of waiting before deciding the file is not there. It should be a very rare event, so it's okay if the user that triggers it has to wait a few seconds while we make sure the selected theme really is gone.

[MichaelH]

Just adding some recent support threads on this:
​http://wordpress.org/support/topic/139546?replies=1
​http://wordpress.org/support/topic/136348?replies=2
​http://wordpress.org/search/revert+to+default+theme?forums=1

[ryan]

How about we just lose this? We reset broken themes when visiting the Presentation admin page. Let's call that good enough.

[lloydbudd]

+1 to removing the call validate_current_theme() from wp-settings.php

file_exists can fails (returns false) when there is file contention. I've been working with a friend who supports a number of busy blogs and on two different hosting environments he has issue with regular resets -- and by regular, I don't mean I can see a pattern to the time interval, sometimes it can be a few minutes a part, sometimes a few hours.

validate_current_theme with its 2 file checks is useful for basic sanity when going to the Presentation tab, and it would be great if it did more checking, but a synchronous wp_file_exists on every load of WP seems awkward, and won't detect most problems with a theme.

[ryan]

(In [6325]) Skip theme validation during normal blog page loads. fixes #3907