(PECL ev >= 0.2.0)
EvSignal watchers will trigger an event when the process receives a specific signal one or more times. Even though signals are very asynchronous, libev will try its best to deliver signals synchronously, i.e. as part of the normal event processing, like any other event.
    There is no limit for the number of watchers for the same signal, but only
    within the same loop, i.e. one can watch for
    SIGINT
    in the default loop and for
    SIGIO
    in another loop, but it is not allowed to watch for
    SIGINT
    in both the default loop and another loop at the same time. At the moment,
    SIGCHLD
    is permanently tied to the default loop.
   
If possible and supported, libev will install its handlers with SA_RESTART (or equivalent) behaviour enabled, so system calls should not be unduly interrupted. In case of a problem with system calls getting interrupted by signals, all the signals can be blocked in an EvCheck watcher and unblocked in a EvPrepare watcher.
$signum
   
   , 
    callable
     $callback
   
   [, 
    mixed
     $data
     = NULL
   
   [, 
    int
     $priority
     = 0
   
  ]] )$signum
   
   , 
    callable
     $callback
   
   [, 
    mixed
     $data
     = NULL
   
   [, 
    int
     $priority
     = 0
   
  ]] )Signal number. See the constants exported by pcntl extension. See also signal(7) man page.