passwd = File.open('/etc/passwd')
puts passwd.fileno
passwd.close
puts passwd.fileno

"""
3
-e:4:in `fileno': closed stream (IOError)
"""

Kernel.exit  # code为1
Kernel.abort "some error messages." # code为1
Kernel.raise # 抛出异常, 如果异常没有被处理则最终会退出

fork do
  puts "hello" # 子进程执行完块后就退出
end

arr = [1]
fork do
  arr << 2
  puts arr # [1, 2]
end

puts arr # [1]

fork do
  5.times do
    sleep 1
    puts "I am an orphan!"
  end
end

Process.wait # 等待一个子进程结束
abort "Parent process died..."

FORK_NUM.times do 
  puts Process.wait # 返回PID
  # puts Process.wait2 # 返回PID和状态码
  # Process.waitpid() # 等待指定PID子进程退出
end

child_processes = 3
dead_processes = 0
# We fork 3 child processes.
child_processes.times do
  fork do
    # They sleep for 3 seconds.
    sleep 3
  end
end

# Sync $stdout so the call to #puts in the CHLD handler isn't
# buffered. Can cause a ThreadError if a signal handler is
# interrupted after calling #puts. Always a good idea to do
# this if your handlers will be doing IO.
$stdout.sync = true

# Our parent process will be busy doing some intense mathematics.
# But still wants to know when one of its children exits.

# By trapping the :CHLD signal our process will be notified by the kernel
# when one of its children exits.
trap(:CHLD) do
  # Since Process.wait queues up any data that it has for us we can ask for it
  # here, since we know that one of our child processes has exited.

  # We loop over a non-blocking Process.wait to ensure that any dead child
  # processes are accounted for.
  begin
    while pid = Process.wait(-1, Process::WNOHANG)
      puts pid
      dead_processes += 1      
    end
  rescue Errno::ECHILD
  end
end

loop do
  # We exit ourself once all the child processes are accounted for.
  exit if dead_processes == child_processes
  
  sleep 1
end

puts Process.pid
trap(:INT) { print "Na na na, you can't get me" }
sleep # so that we have time to send it a signal

reader, writer = IO.pipe
writer.write("Into the pipe I go...")
writer.close
puts reader.read