Resource Types
Semaphore, Shared Memory and IPC Functions
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 |

Resource Types
Semaphore, Shared Memory and IPC Functions
Semaphore
PHP Manual