GX-Entwicklung

Problem:
When a shop has a lot of simultaneous access and meanwhile the shop owner is adding/updating/deleting some information of his shop, the dynamic_theme_style.css.php (responsible for compiling the CSS of the theme) is called multiple times, increasing the page load time of the shop.

Goal:
We should prevent that the CSS compiler runs on every call.
We need to lock the dynamic_theme_style.css.php file until the new CSS is compiled/generated.

How to test:

1. Apply attached patch (optional)
2. Open 2 browser tabs, side by side with the DevTool open (Network tab and filter by CSS)
3. Delete only the cache/__dynamic.css file and call the shop
   1. First tab: CSS should be served with the dynamic_theme_style.css.php
   2. Second tab: CSS should be served with the main.css/main.min.css
4. Delete only the public/theme/main.css or public/theme/main.min.css file and call the shop
   1. Both tabs: CSS should be served with the dynamic_theme_style.css.php
   2. The second tab should wait until the dynamic_theme_style.css.php file of the first tab is loaded
5. Delete cache/__dynamic.css and public/theme/main.css or public/theme/main.min.css files and call the shop
   1. Both tabs: CSS should be served with the dynamic_theme_style.css.php
   2. The second tab should wait until the dynamic_theme_style.css.php file of the first tab is loaded