JRuby issue 2420

jruby_issue_2420.rb

require 'socket'
require 'thread'

port = 2**15 + rand(2**15)
lock = Mutex.new
connections = []
server_socket = TCPServer.new(port)

# this thread is the server, it accepts connections and adds
# them to the connections array
Thread.start do
  loop do
    # wait for new connections, since the real code also did more things
    # all client connections are monitored for readability too
    # this is what causes the problem, if nil is given instead of connections
    # then no exception is raised from this script
    acceptables, _ = IO.select([server_socket], connections, nil, 0)
    if acceptables
      acceptables.each do |socket|
        connection, _ = socket.accept_nonblock
        lock.synchronize do
          connections << connection
        end
      end
    end
  end
end

# make ten connections to the server
Array.new(10) { TCPSocket.new('localhost', port) }

# wait util the server has accepted all ten connections
until lock.synchronize { connections.size == 10 }
  sleep 0.01
end

# write a message to all connected clients
lock.synchronize do
  connections.each do |socket|
    if IO.select(nil, [socket], nil, 0)
      begin
        # this raises java.nio.channels.IllegalBlockingModeException in JRuby 9K
        # when the socket is also monitored for writability in the server thread
        # this does not raise an error in JRuby 1.7 nor MRI
        socket.write_nonblock('hello world')
      rescue => e
        $stderr.puts('#write_nonblock failed with "%s" (%s)' % [e.message, e.class.name])
      end
    end
  end
end