minor #10498 PhpFilesAdapter not invalidating cache when opcache does not validate file timestamps (arno14)

This PR was merged into the 3.4 branch.

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PhpFilesAdapter not invalidating cache when opcache does not validate file timestamps

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Commits
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a886416 PhpFilesAdapter not invalidating cache

Author: javiereguiluz

components/cache/adapters/php_files_adapter.rst

@@ -32,7 +32,12 @@ file similar to the following::
     As cache items are included and parsed as native PHP code and due to the way `OPcache`_
     handles file includes, this adapter has the potential to be much faster than other
     filesystem-based caches.
-
+    
+.. caution::
+   If you have configured Opcache to not check the files timestamps 
+   (see https://symfony.com/doc/current/performance.html#performance-dont-check-timestamps),
+   the cached items will not not be invalidated unless you clear the opcache.
+   
 The PhpFilesAdapter can optionally be provided a namespace, default cache lifetime, and cache
 directory path as constructor arguments::