When an anonymous user tries to view a page without sufficient permissions, view cache generation is still started and later aborted.
Under high traffic/concurrency conditions, this can create cache "locks", where processes wait for previous .generating files to complete, until timeout is reached.

Steps to reproduce

• Remove content/read permissions (for article, section, or globally) from a user (like anonymous).
• Access the site as the user, verify that the login page is displayed.
• Simulate a high-concurrency scenario (like apachebench, using concurrency of 200) requesting that page.
• Verify that some requests will take over 60 seconds (waiting for the viewcache to finish generating).