From: Josh <josh.m.sharpe@...>
Date: 2010-09-07T05:10:18+09:00
Subject: trouble with mkfifo and forks

# In a nutshell:
1) Create a pipe
2) Fork twice
3) Each for sends 10 strings over the pipe
4) See what comes out the other side

So, why isn't what I send coming out?

class WaitListTest < Test::Unit::TestCase
  NUMBER_OF_ORDERS = 2
  PIPE = "test/wl_pipe"

  def setup
    `rm #{PIPE}`
    `mkfifo #{PIPE}`
  end

  def test_registering_last_race
    term_count = 0
    responses = []
    pids = []

    NUMBER_OF_ORDERS.times do |i|
      pids << Process.fork do
        sleep 1 + (0.1 * i)
        10.times do |a|
          File.open("#{RAILS_ROOT}/#{PIPE}", "w+") do |pipe|
            sleep 0.1
            pipe.puts "Fork #{i} - #{a}"
          end
        end
        File.open("#{RAILS_ROOT}/#{PIPE}", "a") do |pipe|
          sleep 0.1
          pipe.puts "DONE"
        end
      end
    end

    while term_count < NUMBER_OF_ORDERS
      File.open("#{RAILS_ROOT}/#{PIPE}", "r+") do |pipe|
        val = pipe.gets
        if val.match(/DONE/)
          term_count += 1
        else
          responses << val
        end
      end
    end
    puts responses.sort
    puts responses.count
  end
end

# output
Started
Fork 0 - 0
Fork 0 - 1
Fork 0 - 2
Fork 0 - 3
Fork 0 - 4
Fork 0 - 5
Fork 0 - 7
Fork 0 - 9
Fork 1 - 0
Fork 1 - 1
Fork 1 - 2
Fork 1 - 3
Fork 1 - 4
Fork 1 - 5
Fork 1 - 7
Fork 1 - 8
Fork 1 - 9
17

Why isn't this 20?