(PECL ev >= 0.2.0)
EvIo watchers check whether a file descriptor(or socket, or a stream castable to numeric file descriptor) is readable or writable in each iteration of the event loop, or, more precisely, when reading would not block the process and writing would at least be able to write some data. This behaviour is called level-triggering because events are kept receiving as long as the condition persists. To stop receiving events just stop the watcher.
    The number of read and/or write event watchers per
    fd
    is unlimited. Setting all file descriptors to non-blocking mode is also
    usually a good idea(but not required).
   
    Another thing to watch out for is that it is quite easy to receive false
    readiness notifications, i.e. the callback might be called with
    Ev::READ
    but a subsequent
    read()
    will actually block because there is no data. It is very easy to get into
    this situation. Thus it is best to always use non-blocking I/O: An extra
    read()
    returning
    EAGAIN
    (or similar) is far preferable to a program hanging until some data
    arrives.
   
    If for some reason it is impossible to run the
    fd
    in non-blocking mode, then separately re-test whether a file descriptor is
    really ready. Some people additionally use
    SIGALRM
    and an interval timer, just to be sure thry won't block infinitely.
   
Always consider using non-blocking mode.
$fd
   
   , 
    int
     $events
   
   , 
    callable
     $callback
   
   [, 
    mixed
     $data
   
   [, 
    int
     $priority
   
  ]] )$fd
   
   , 
    int
     $events
   
   , 
    callable
     $callback
   
   [, 
    mixed
     $data
     = NULL
   
   [, 
    int
     $priority
     = 0
   
  ]] )