sem_acquire while loop can lead to 100% CPU load
PHP FPM 5.5.6 / 5.5.21 (tested before and after update)
TYPO3 6.2.14 with semaphore locking
After a cache clear via admin interface, a siege run with more than 3-4 users leads to at least one timed out response. The FPM process serving that requests uses 100% CPU till PHP timeout. Using the recommended timeout setting of 240, this quickly leads to an unresponsive server at just medium traffic. A lower timeout setting mitigates the problem.
Just like before 6.2, and like 7.3+, the lock acquiration should not be attempted in a loop. After a failed lock, an exception should be thrown, same as the other locking mechanisms.