Semaphore
PHP Manual

Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

System V message constants
Constant Type Changelog
MSG_IPC_NOWAIT integer  
MSG_EAGAIN integer As of 5.2.0
MSG_ENOMSG integer As of 5.2.0
MSG_NOERROR integer  
MSG_EXCEPT integer  


Semaphore
PHP Manual