Watcher callbacks

All watchers can be active(waiting for events) or inactive(paused). Only active watchers will have their callbacks invoked. All callbacks will be called with at least two arguments: watcher - the watcher, and revents a bitmask of received events.

Watcher callbacks are passed to the watcher constructors (the classes derived from EvWatcher - EvCheck::__construct(), EvChild::__construct() etc.). A watcher callback should match the following prototype:

function callback( object $watcher = NULL , int $revents = NULL ): void

watcher: The watcher instance(of a class extending EvWatcher ).
revents: Watcher received events.

Each watcher type has its associated bit in revents, so one can use the same callback for multiple watchers. The event mask is named after the type, i.e. EvChild (or EvLoop::child()) sets Ev::CHILD, EvPrepare (or EvLoop::prepare()) sets Ev::PREPARE, EvPeriodic (or EvLoop::periodic()) sets Ev::PERIODIC and so on, with the exception of I/O events (which can set both Ev::READ and Ev::WRITE bits).