Add logging to io_read.

Author: ioquatix

lib/io/event/selector/select.rb

@@ -170,7 +170,9 @@ def io_read(fiber, io, buffer, length, offset = 0)
 
 					Selector.nonblock(io) do
 						while true
+							Fiber.blocking{$stderr.puts "buffer.read(#{io}, 0, #{offset})"}
 							result = Fiber.blocking{buffer.read(io, 0, offset)}
+							Fiber.blocking{$stderr.puts "buffer.read(#{io}, 0, #{offset}) => #{result}"}
 
 							if result < 0
 								if again?(result)