(PECL ev >= 0.2.0)
Ev::depth — Returns recursion depth
   The number of times
   Ev::run()
   was entered minus the number of times
   Ev::run()
   was exited normally, in other words, the recursion depth. Outside
   Ev::run()
   , this number is
   0
   . In a callback, this number is
   1
   , unless
   Ev::run()
   was invoked recursively (or from another thread), in which case it is
   higher.
  
This function has no parameters.
ev_depth() returns recursion depth of the default loop.