require 'epoll'

# Epoll < IO

# Epoll.create
#   call epoll_create(2)
#   it's just alias of `open`
#   Epoll object stock a File Descriptor returned by epoll_create(2)
#   return: instance of Epoll (kind of IO)
epoll = Epoll.create

# IO object add to interest list
#   call epoll_ctl(2)
epoll.add(io, Epoll::IN)  # same way to epoll.ctl(Epoll::CTL_ADD, io, Epoll::IN)

# change waiting events
#   call epoll_ctl(2)
epoll.mod(io, Epoll::OUT) # same way to epoll.ctl(Epoll::CTL_MOD, io, Epoll::OUT)

# remove from interest list
#   call epoll_ctl(2)
epoll.del(io)             # same way to epoll.ctl(Epoll::CTL_DEL, io)

loop do
  # Epoll#wait(timeout=-1)
  #   call epoll_wait(2)
  #   timeout = -1: block until receive event or signals
  #   timeout = 0: return all io's can I/O on non block
  #   timeout > 0: block when timeout pass miri second or receive events or signals
  #   return: Array of Epoll::Event
  evlist = epoll.wait

  # ev is instance of Epoll::Event like `struct epoll_event`
  # it's instance of `class Epoll::Event < Struct.new(:data, :events); end`
  evlist.each do |ev|
    # Epoll::Event#events is event flag bits (Fixnum)
    if (ev.events & Epoll::IN) != 0
      # Epoll::Event#data is notified IO (IO)
      # e.g. it's expect to I/O readable
      puts ev.data.read
    elsif (ev.events & Epoll::HUP|Epoll::ERR) != 0
      ev.data.close
      break
    end
  end
end

# you can close File Descriptor for epoll when finish to use
epoll.close #=> nil

# and you can check closed
epoll.closed? #=> true

# and very useful way is that call `create` with block like `IO.open`
# return: block result
Epoll.create do |epoll|
  # ensure automatic call `epoll.close` when out block
end