TYPO3 Core

Since https://review.typo3.org/24073 installing new extensions may lead to fatal PHP errors if new classes are added which rely on the autoloader.
The handling of NULL and 0 values for lifetime fails because $GLOBALS['EXEC_TIME'] is not set yet when the autoloader is invoked.
The expiry time for NULL lifetime values is set to the default lifetime (3600) plus EXEC_TIME (0).

When checking if a cache entry is valid or not, a check is done if expiry time in cache entry != 0 and < EXEC_TIME. Since EXEC_TIME is zero this will never fail.
Same problem in flushByTag() which first finds the cache entries with a similar check. The result is that these autoload cache files are not removed.

To make the feature work EXEC_TIME must be set before activating the caches and autoloader. For testing I copied it to the top of config_default.php and the right expiry times appear in the cache entries. Installing an extension with new classes now works without fatal errors.