In, a Twig template cache race condition was found, which caused some sites, in some circumstances, to have fatal errors that required manual cache clearing or other specialized fixes.
Most of the ways to reproduce the bug involve extensive/elaborate manual process, and while there was one simple automated test added, it didn't thoroughly reproduce scenarios that can lead to the Twig template race condition, e.g.:
- High traffic site with multiple PHP-FPM processes that end up not writing the Twig template file correctly.
- Shared / slow filesystems for generated Twig template storage, causing the fatal error on first page load (but it clears on on second page load).
- Other mysterious occurrences which are not well understood... but happened nonetheless!
Write some tests to test for the race condition in the Twig template cache.
User interface changes
Data model changes