(PECL ev >= 0.2.0)
Ev::recommendedBackends — Returns a bit mask of recommended backends for current platform
   Returns the set of all backends compiled into this binary of
   libev
   and also recommended for this platform, meaning it will work for most file
   descriptor types. This set is often smaller than the one returned by
   ev_supported_backends()
   , as for example
   kqueue
   is broken on most
   BSD
   systems and will not be auto-detected unless it is requested explicitly.
   This is the set of backends that
   libev
   will probe no backends specified explicitly.
  
Diese Funktion besitzt keine Parameter.
Returns a bit mask which can containing backend flags combined using bitwise OR operator.
Beispiel #1 Embedding one loop into another
<?php
/*
* Try to get an embeddable event loop and embed it into the default event loop.
* If it is impossible, use the default
* loop. The default loop is stored in $loop_hi, while the embeddable loop is
* stored in $loop_lo(which is $loop_hi in the case no embeddable loop can be
* used).
*
* Sample translated to PHP
* http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod#Examples_CONTENT-9
*/
$loop_hi = EvLoop::defaultLoop();
$loop_lo = NULL;
$embed   = NULL;
/*
* See if there is a chance of getting one that works
* (flags' value of 0 means autodetection)
*/
$loop_lo = Ev::embeddableBackends() & Ev::recommendedBackends()
 ? new EvLoop(Ev::embeddableBackends() & Ev::recommendedBackends())
 : 0;
if ($loop_lo) {
 $embed = new EvEmbed($loop_lo, function () {});
} else {
 $loop_lo = $loop_hi;
}
?>