As discussed kgio is no longer absolutely necessary.

We can use Ruby 2+ non blocking IO capabilities instead.

Also available at https://github.com/casperisfine/unicorn.git (remove-kgio)

---
  lib/unicorn.rb                 |  3 +--
  lib/unicorn/http_request.rb    | 15 +++++++++-----
  lib/unicorn/http_server.rb     | 33 +++++++++++++++++++++--------
  lib/unicorn/socket_helper.rb   | 20 ++++--------------
  lib/unicorn/stream_input.rb    | 16 ++++++++------
  lib/unicorn/worker.rb          | 38 ++++++++++++++++++++++------------
  t/oob_gc.ru                    |  2 +-
  t/oob_gc_path.ru               |  2 +-
  test/unit/test_request.rb      | 16 +++-----------
  test/unit/test_stream_input.rb |  7 ++-----
  test/unit/test_tee_input.rb    |  2 +-
  unicorn.gemspec                |  1 -
  12 files changed, 82 insertions(+), 73 deletions(-)

diff --git a/lib/unicorn.rb b/lib/unicorn.rb
index 1a50631..170719c 100644
--- a/lib/unicorn.rb
+++ b/lib/unicorn.rb
@@ -1,7 +1,6 @@
  # -*- encoding: binary -*-
  require 'etc'
  require 'stringio'
-require 'kgio'
  require 'raindrops'
  require 'io/wait'

@@ -113,7 +112,7 @@ def self.log_error(logger, prefix, exc)
    F_SETPIPE_SZ = 1031 if RUBY_PLATFORM =~ /linux/

    def self.pipe # :nodoc:
-    Kgio::Pipe.new.each do |io|
+    IO.pipe.each do |io|
        # shrink pipes to minimize impact on 
/proc/sys/fs/pipe-user-pages-soft
        # limits.
        if defined?(F_SETPIPE_SZ)
diff --git a/lib/unicorn/http_request.rb b/lib/unicorn/http_request.rb
index e3ad592..7f7324b 100644
--- a/lib/unicorn/http_request.rb
+++ b/lib/unicorn/http_request.rb
@@ -71,14 +71,19 @@ def read(socket)
      #  identify the client for the immediate request to the server;
      #  that client may be a proxy, gateway, or other intermediary
      #  acting on behalf of the actual source client."
-    e['REMOTE_ADDR'] = socket.kgio_addr
+    address = socket.remote_address
+    e['REMOTE_ADDR'] = if address.unix?
+      "127.0.0.1"
+    else
+      address.ip_address
+    end

      # short circuit the common case with small GET requests first
-    socket.kgio_read!(16384, buf)
+    socket.readpartial(16384, buf)
      if parse.nil?
        # Parser is not done, queue up more data to read and continue 
parsing
        # an Exception thrown from the parser will throw us out of the loop
-      false until add_parse(socket.kgio_read!(16384))
+      false until add_parse(socket.readpartial(16384))
      end

      check_client_connection(socket) if @@check_client_connection
@@ -108,7 +113,7 @@ def hijacked?
      TCPI = Raindrops::TCP_Info.allocate

      def check_client_connection(socket) # :nodoc:
-      if Unicorn::TCPClient === socket
+      if TCPSocket === socket
          # Raindrops::TCP_Info#get!, #state (reads struct 
tcp_info#tcpi_state)
          raise Errno::EPIPE, "client closed connection".freeze,
                EMPTY_ARRAY if closed_state?(TCPI.get!(socket).state)
@@ -153,7 +158,7 @@ def closed_state?(state) # :nodoc:
      # Not that efficient, but probably still better than doing unnecessary
      # work after a client gives up.
      def check_client_connection(socket) # :nodoc:
-      if Unicorn::TCPClient === socket && @@tcpi_inspect_ok
+      if TCPSocket === socket && @@tcpi_inspect_ok
          opt = socket.getsockopt(Socket::IPPROTO_TCP, 
Socket::TCP_INFO).inspect
          if opt =~ /\bstate=(\S+)/
            raise Errno::EPIPE, "client closed connection".freeze,
diff --git a/lib/unicorn/http_server.rb b/lib/unicorn/http_server.rb
index 21f2a05..98cd119 100644
--- a/lib/unicorn/http_server.rb
+++ b/lib/unicorn/http_server.rb
@@ -111,7 +111,7 @@ def initialize(app, options = {})
      @worker_data = if worker_data = ENV['UNICORN_WORKER']
        worker_data = worker_data.split(',').map!(&:to_i)
        worker_data[1] = worker_data.slice!(1..2).map do |i|
-        Kgio::Pipe.for_fd(i)
+        IO.for_fd(i)
        end
        worker_data
      end
@@ -240,7 +240,7 @@ def listen(address, opt = 
{}.merge(listener_opts[address] || {}))
      tries = opt[:tries] || 5
      begin
        io = bind_listen(address, opt)
-      unless Kgio::TCPServer === io || Kgio::UNIXServer === io
+      unless TCPServer === io || UNIXServer === io
          io.autoclose = false
          io = server_cast(io)
        end
@@ -386,12 +386,18 @@ def master_sleep(sec)
      # the Ruby itself and not require a separate malloc (on 32-bit MRI 
1.9+).
      # Most reads are only one byte here and uncommon, so it's not worth a
      # persistent buffer, either:
-    @self_pipe[0].kgio_tryread(11)
+    begin
+      @self_pipe[0].read_nonblock(11)
+    rescue Errno::EAGAIN
+    end
    end

    def awaken_master
      return if $$ != @master_pid
-    @self_pipe[1].kgio_trywrite('.') # wakeup master process from select
+    begin
+      @self_pipe[1].write_nonblock('.') # wakeup master process from select
+    rescue Errno::EAGAIN
+    end
    end

    # reaps all unreaped workers
@@ -581,7 +587,10 @@ def handle_error(client, e)
        500
      end
      if code
-      client.kgio_trywrite(err_response(code, 
@request.response_start_sent))
+      begin
+        client.write_nonblock(err_response(code, 
@request.response_start_sent))
+      rescue Errno::EAGAIN
+      end
      end
      client.close
    rescue
@@ -733,9 +742,15 @@ def worker_loop(worker)
        reopen = reopen_worker_logs(worker.nr) if reopen
        worker.tick = time_now.to_i
        while sock = ready.shift
-        # Unicorn::Worker#kgio_tryaccept is not like accept(2) at all,
+        # Unicorn::Worker#accept_nonblock is not like accept(2) at all,
          # but that will return false
-        if client = sock.kgio_tryaccept
+        client = begin
+          sock.accept_nonblock
+        rescue Errno::EAGAIN
+          false
+        end
+
+        if client
            process_client(client)
            worker.tick = time_now.to_i
          end
@@ -834,7 +849,7 @@ def redirect_io(io, path)

    def inherit_listeners!
      # inherit sockets from parents, they need to be plain Socket objects
-    # before they become Kgio::UNIXServer or Kgio::TCPServer
+    # before they become UNIXServer or TCPServer
      inherited = ENV['UNICORN_FD'].to_s.split(',')

      # emulate sd_listen_fds() for systemd
@@ -858,7 +873,7 @@ def inherit_listeners!
      LISTENERS.replace(inherited)

      # we start out with generic Socket objects that get cast to either
-    # Kgio::TCPServer or Kgio::UNIXServer objects; but since the Socket
+    # TCPServer or UNIXServer objects; but since the Socket
      # objects share the same OS-level file descriptor as the higher-level
      # *Server objects; we need to prevent Socket objects from being
      # garbage-collected
diff --git a/lib/unicorn/socket_helper.rb b/lib/unicorn/socket_helper.rb
index 8a6f6ee..9d2ba52 100644
--- a/lib/unicorn/socket_helper.rb
+++ b/lib/unicorn/socket_helper.rb
@@ -3,18 +3,6 @@
  require 'socket'

  module Unicorn
-
-  # Instead of using a generic Kgio::Socket for everything,
-  # tag TCP sockets so we can use TCP_INFO under Linux without
-  # incurring extra syscalls for Unix domain sockets.
-  # TODO: remove these when we remove kgio
-  TCPClient = Class.new(Kgio::Socket) # :nodoc:
-  class TCPSrv < Kgio::TCPServer # :nodoc:
-    def kgio_tryaccept # :nodoc:
-      super(TCPClient)
-    end
-  end
-
    module SocketHelper

      # internal interface
@@ -135,7 +123,7 @@ def bind_listen(address = '0.0.0.0:8080', opt = {})
          end
          old_umask = File.umask(opt[:umask] || 0)
          begin
-          Kgio::UNIXServer.new(address)
+          UNIXServer.new(address)
          ensure
            File.umask(old_umask)
          end
@@ -164,7 +152,7 @@ def new_tcp_server(addr, port, opt)
        end
        sock.bind(Socket.pack_sockaddr_in(port, addr))
        sock.autoclose = false
-      TCPSrv.for_fd(sock.fileno)
+      TCPServer.for_fd(sock.fileno)
      end

      # returns rfc2732-style (e.g. "[::1]:666") addresses for IPv6
@@ -201,9 +189,9 @@ def sock_name(sock)
      def server_cast(sock)
        begin
          Socket.unpack_sockaddr_in(sock.getsockname)
-        TCPSrv.for_fd(sock.fileno)
+        TCPServer.for_fd(sock.fileno)
        rescue ArgumentError
-        Kgio::UNIXServer.for_fd(sock.fileno)
+        UNIXServer.for_fd(sock.fileno)
        end
      end

diff --git a/lib/unicorn/stream_input.rb b/lib/unicorn/stream_input.rb
index 41d28a0..3241ff4 100644
--- a/lib/unicorn/stream_input.rb
+++ b/lib/unicorn/stream_input.rb
@@ -1,3 +1,4 @@
+
  # -*- encoding: binary -*-

  # When processing uploads, unicorn may expose a StreamInput object under
@@ -49,7 +50,11 @@ def read(length = nil, rv = '')
          to_read = length - @rbuf.size
          rv.replace(@rbuf.slice!(0, @rbuf.size))
          until to_read == 0 || eof? || (rv.size > 0 && @chunked)
-          @socket.kgio_read(to_read, @buf) or eof!
+          begin
+            @socket.readpartial(to_read, @buf)
+          rescue EOFError
+            eof!
+          end
            filter_body(@rbuf, @buf)
            rv << @rbuf
            to_read -= @rbuf.size
@@ -72,8 +77,7 @@ def read(length = nil, rv = '')
    # Returns nil if called at the end of file.
    # This takes zero arguments for strict Rack::Lint compatibility,
    # unlike IO#gets.
-  def gets
-    sep = $/
+  def gets(sep = $/)
      if sep.nil?
        read_all(rv = '')
        return rv.empty? ? nil : rv
@@ -83,7 +87,7 @@ def gets
      begin
        @rbuf.sub!(re, '') and return $1
        return @rbuf.empty? ? nil : @rbuf.slice!(0, @rbuf.size) if eof?
-      @socket.kgio_read(@@io_chunk_size, @buf) or eof!
+      @socket.readpartial(@@io_chunk_size, @buf) or eof!
        filter_body(once = '', @buf)
        @rbuf << once
      end while true
@@ -107,7 +111,7 @@ def each
    def eof?
      if @parser.body_eof?
        while @chunked && ! @parser.parse
-        once = @socket.kgio_read(@@io_chunk_size) or eof!
+        once = @socket.readpartial(@@io_chunk_size) or eof!
          @buf << once
        end
        @socket = nil
@@ -127,7 +131,7 @@ def read_all(dst)
      dst.replace(@rbuf)
      @socket or return
      until eof?
-      @socket.kgio_read(@@io_chunk_size, @buf) or eof!
+      @socket.readpartial(@@io_chunk_size, @buf) or eof!
        filter_body(@rbuf, @buf)
        dst << @rbuf
      end
diff --git a/lib/unicorn/worker.rb b/lib/unicorn/worker.rb
index 5ddf379..fe741c0 100644
--- a/lib/unicorn/worker.rb
+++ b/lib/unicorn/worker.rb
@@ -63,27 +63,39 @@ def soft_kill(sig) # :nodoc:
        signum = Signal.list[sig.to_s] or
            raise ArgumentError, "BUG: bad signal: #{sig.inspect}"
      end
+
      # writing and reading 4 bytes on a pipe is atomic on all POSIX 
platforms
      # Do not care in the odd case the buffer is full, here.
-    @master.kgio_trywrite([signum].pack('l'))
+    begin
+      @master.write_nonblock([signum].pack('l'))
+    rescue Errno::EAGAIN
+    end
    rescue Errno::EPIPE
      # worker will be reaped soon
    end

    # this only runs when the Rack app.call is not running
    # act like a listener
-  def kgio_tryaccept # :nodoc:
-    case buf = @to_io.kgio_tryread(4)
-    when String
-      # unpack the buffer and trigger the signal handler
-      signum = buf.unpack('l')
-      fake_sig(signum[0])
-      # keep looping, more signals may be queued
-    when nil # EOF: master died, but we are at a safe place to exit
-      fake_sig(:QUIT)
-    when :wait_readable # keep waiting
-      return false
-    end while true # loop, as multiple signals may be sent
+  def accept_nonblock # :nodoc:
+    loop do
+      buf = begin
+        @to_io.read_nonblock(4)
+      rescue Errno::EAGAIN # keep waiting
+        return false
+      rescue EOFError # master died, but we are at a safe place to exit
+        fake_sig(:QUIT)
+      end
+
+      case buf
+      when String
+        # unpack the buffer and trigger the signal handler
+        signum = buf.unpack('l')
+        fake_sig(signum[0])
+        # keep looping, more signals may be queued
+      else
+        raise TypeError, "Unexpected read_nonblock returns: #{buf.inspect}"
+      end
+    end # loop, as multiple signals may be sent
    end

    # worker objects may be compared to just plain Integers
diff --git a/t/oob_gc.ru b/t/oob_gc.ru
index c253540..43c0f68 100644
--- a/t/oob_gc.ru
+++ b/t/oob_gc.ru
@@ -7,7 +7,7 @@

  # Mock GC.start
  def GC.start
-  ObjectSpace.each_object(Kgio::Socket) do |x|
+  ObjectSpace.each_object(Socket) do |x|
      x.closed? or abort "not closed #{x}"
    end
    $gc_started = true
diff --git a/t/oob_gc_path.ru b/t/oob_gc_path.ru
index af8e3b9..e772261 100644
--- a/t/oob_gc_path.ru
+++ b/t/oob_gc_path.ru
@@ -7,7 +7,7 @@

  # Mock GC.start
  def GC.start
-  ObjectSpace.each_object(Kgio::Socket) do |x|
+  ObjectSpace.each_object(Socket) do |x|
      x.closed? or abort "not closed #{x}"
    end
    $gc_started = true
diff --git a/test/unit/test_request.rb b/test/unit/test_request.rb
index 6cb0268..a951057 100644
--- a/test/unit/test_request.rb
+++ b/test/unit/test_request.rb
@@ -11,11 +11,8 @@
  class RequestTest < Test::Unit::TestCase

    class MockRequest < StringIO
-    alias_method :readpartial, :sysread
-    alias_method :kgio_read!, :sysread
-    alias_method :read_nonblock, :sysread
-    def kgio_addr
-      '127.0.0.1'
+    def remote_address
+      Addrinfo.tcp('127.0.0.1', 55608)
      end
    end

@@ -152,14 +149,7 @@ def test_rack_lint_big_put
      buf = (' ' * bs).freeze
      length = bs * count
      client = Tempfile.new('big_put')
-    def client.kgio_addr; '127.0.0.1'; end
-    def client.kgio_read(*args)
-      readpartial(*args)
-    rescue EOFError
-    end
-    def client.kgio_read!(*args)
-      readpartial(*args)
-    end
+    def client.remote_address; Addrinfo.tcp('127.0.0.1', 55608); end
      client.syswrite(
        "PUT / HTTP/1.1\r\n" \
        "Host: foo\r\n" \
diff --git a/test/unit/test_stream_input.rb b/test/unit/test_stream_input.rb
index 1a07ec3..445b415 100644
--- a/test/unit/test_stream_input.rb
+++ b/test/unit/test_stream_input.rb
@@ -6,16 +6,14 @@

  class TestStreamInput < Test::Unit::TestCase
    def setup
-    @rs = $/
      @env = {}
-    @rd, @wr = Kgio::UNIXSocket.pair
+    @rd, @wr = UNIXSocket.pair
      @rd.sync = @wr.sync = true
      @start_pid = $$
    end

    def teardown
      return if $$ != @start_pid
-    $/ = @rs
      @rd.close rescue nil
      @wr.close rescue nil
      Process.waitall
@@ -54,10 +52,9 @@ def test_gets_multiline
    end

    def test_gets_empty_rs
-    $/ = nil
      r = init_request("a\nb\n\n")
      si = Unicorn::StreamInput.new(@rd, r)
-    assert_equal "a\nb\n\n", si.gets
+    assert_equal "a\nb\n\n", si.gets(nil)
      assert_nil si.gets
    end

diff --git a/test/unit/test_tee_input.rb b/test/unit/test_tee_input.rb
index 4647e66..21b90f1 100644
--- a/test/unit/test_tee_input.rb
+++ b/test/unit/test_tee_input.rb
@@ -12,7 +12,7 @@ class TestTeeInput < Test::Unit::TestCase

    def setup
      @rs = $/
-    @rd, @wr = Kgio::UNIXSocket.pair
+    @rd, @wr = UNIXSocket.pair
      @rd.sync = @wr.sync = true
      @start_pid = $$
    end
diff --git a/unicorn.gemspec b/unicorn.gemspec
index 7bb1154..85183d9 100644
--- a/unicorn.gemspec
+++ b/unicorn.gemspec
@@ -36,7 +36,6 @@
    # won't have descriptive text, only the numeric status.
    s.add_development_dependency(%q<rack>)

-  s.add_dependency(%q<kgio>, '~> 2.6')
    s.add_dependency(%q<raindrops>, '~> 0.7')

    s.add_development_dependency('test-unit', '~> 3.0')
-- 
2.35.1