# -*- encoding: binary -*-
# Copyright (C) 2013-2016 all contributors <yahns-public@yhbt.net>
# License: GPL-3.0+ (https://www.gnu.org/licenses/gpl-3.0.txt)
# frozen_string_literal: true
#
# This is the dangerous, low-level epoll interface for sleepy_penguin
# It is safe as long as you're aware of all potential concurrency
# issues given multithreading, GC, and epoll itself.
class Yahns::Queue < SleepyPenguin::Epoll::IO # :nodoc:
  include SleepyPenguin
  attr_accessor :fdmap # Yahns::Fdmap

  # public
  QEV_QUIT = Epoll::OUT # Level Trigger for QueueQuitter
  QEV_RD = Epoll::IN | Epoll::ONESHOT
  QEV_WR = Epoll::OUT | Epoll::ONESHOT

  def self.new
    super(Epoll::CLOEXEC)
  end

  # for HTTP and HTTPS servers, we rely on the io writing to us, first
  # flags: QEV_RD/QEV_WR (usually QEV_RD)
  def queue_add(io, flags)
    # order is very important here, this thread cannot do anything with
    # io once we've issued epoll_ctl() because another thread may use it
    @fdmap.add(io)
    epoll_ctl(Epoll::CTL_ADD, io, flags)
  end

  def queue_mod(io, flags)
    epoll_ctl(Epoll::CTL_MOD, io, flags)
  end

  def thr_init
    Thread.current[:yahns_rbuf] = ''.dup
    Thread.current[:yahns_fdmap] = @fdmap
    Thread.current[:yahns_queue] = self
  end

  # returns an infinitely running thread
  def worker_thread(logger, max_events)
    Thread.new do
      thr_init
      begin
        epoll_wait(max_events) do |_, io| # don't care for flags for now
          next if io.closed?

          # Note: we absolutely must not do anything with io after
          # we've called epoll_ctl on it, io is exclusive to this
          # thread only until epoll_ctl is called on it.
          case rv = io.yahns_step
          when :wait_readable
            epoll_ctl(Epoll::CTL_MOD, io, QEV_RD)
          when :wait_writable
            epoll_ctl(Epoll::CTL_MOD, io, QEV_WR)
          when :ignore # only used by rack.hijack
            # we cannot call Epoll::CTL_DEL after hijacking, the hijacker
            # may have already closed it  Likewise, io.fileno is not
            # expected to work, so we had to erase it from fdmap before hijack
          when nil, :close
            # this must be the ONLY place where we call IO#close on
            # things that got inside the queue AND fdmap
            @fdmap.sync_close(io)
          else
            raise "BUG: #{io.inspect}#yahns_step returned: #{rv.inspect}"
          end
        end
      rescue StandardError, LoadError, SyntaxError => e
        break if closed? # can still happen due to shutdown_timeout
        Yahns::Log.exception(logger, 'queue loop', e)
      end while true
    end
  end
end