Making the API for the balancing queue more symmetric with `Callbacks…

….on_select` for easier customizing of behavior

examples/balancing.rb

@@ -63,9 +63,7 @@ def self.select(strategy = :balanced)
           raise ArgumentError, "Unknown strategy: #{@strategy}"
       end
 
-      puts "---> Selecting #{backend}" if STDOUT.tty?
-      backend.increment_counter if Backend.strategy == :balanced
-
+      Callbacks.on_select.call(backend)
       yield backend if block_given?
       backend
     end
@@ -102,6 +100,13 @@ module Callbacks
     include ANSI::Code
     extend  self
 
+    def on_select
+      lambda do |backend|
+        puts black_on_white { 'on_select'.ljust(12) } + " #{backend.inspect}"
+        backend.increment_counter if Backend.strategy == :balanced
+      end
+    end
+
     def on_connect
       lambda do |backend|
         puts black_on_magenta { 'on_connect'.ljust(12) } + ' ' + bold { backend }