Ruby/Threads/fork

ENV["alpha"] = "123"
ENV["beta"]  = "456"
fork do   
  x = ENV["alpha"]
  ENV["beta"] = "789"
  y = ENV["beta"]
  puts " Child: alpha = #{x}"
  puts " Child: beta  = #{y}"
end
Process.wait
a = ENV["alpha"]
b = ENV["beta"]
puts "Parent: alpha = #{a}"
puts "Parent: beta  = #{b}"

fork {
  puts "Hello from the child process: #$$"
}
puts "Hello from the parent process: #$$"

require "socket"
server = TCPServer.new(1234)
5.times do
  fork do
    while connection = server.accept
      while line = connection.gets
        break if line =~ /quit/
        puts line
        connection.puts "Received!"
      end
      connection.puts "Closing the connection. Bye!"
      connection.close
    end
  end
end

# fork returns the child process"s process ID in the parent, but nil in the child process
# You can use this to determine which process a script is in. 
# forks the current process into two processes, and only executes the exec command within the child process (the process generated by the fork):
if fork.nil?
  exec "ruby some_other_file.rb"
end
puts "This Ruby script now runs alongside some_other_file.rb"

fork do 
    puts "In child, pid = #$$" 
    exit 99 
end 
pid = Process.wait 
puts "Child terminated, pid = #{pid}, status = #{$?.exitstatus}"

pid = fork
if (pid)
  puts "Hello from parent process: #$$"
  puts "Created child process #{pid}"
else
  puts "Hello from child process: #$$"
end