Libevent
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.

EV_TIMEOUT (integer)
EV_READ (integer)
EV_WRITE (integer)
EV_SIGNAL (integer)
EV_PERSIST (integer)
EVLOOP_NONBLOCK (integer)
EVLOOP_ONCE (integer)

Libevent
PHP Manual