He lists five different pain points he discovered when trying to use the extension:

• Lack of a true Semaphore
• Undefined error handling
• Undefined behavior of sem_get()
• Cannot disable semaphore auto-releasing
• A semaphore may be deleted when other processes are waiting to acquire it

The semaphore extension provides a PHP-based wrapper for the System V IPC family of functions (including semaphores, shared memory and inter-process messaging).