Module: Daemonize

Defined in:
lib/daemons/daemonize.rb

Class Method Summary collapse

Class Method Details

.call_as_daemon(block, logfile_name = nil, app_name = nil) ⇒ Object

Call a given block as a daemon


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# File 'lib/daemons/daemonize.rb', line 41

def call_as_daemon(block, logfile_name = nil, app_name = nil)
  # we use a pipe to return the PID of the daemon
  rd, wr = IO.pipe

  if tmppid = safefork
    # in the parent

    wr.close
    pid = rd.read.to_i
    rd.close

    Process.waitpid(tmppid)

    return pid
  else
    # in the child

    rd.close

    # Detach from the controlling terminal
    unless sess_id = Process.setsid
      fail Daemons.RuntimeException.new('cannot detach from controlling terminal')
    end

    # Prevent the possibility of acquiring a controlling terminal
    trap 'SIGHUP', 'IGNORE'
    exit if pid = safefork

    wr.write Process.pid
    wr.close

    $0 = app_name if app_name

    # Release old working directory
    Dir.chdir '/'

    close_io

    redirect_io(logfile_name)

    # Split rand streams between spawning and daemonized process
    srand

    block.call

    exit
  end
end

.close_ioObject


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# File 'lib/daemons/daemonize.rb', line 121

def close_io
  # Make sure all input/output streams are closed
  # Part I: close all IO objects (except for STDIN/STDOUT/STDERR)
  ObjectSpace.each_object(IO) do |io|
    unless [STDIN, STDOUT, STDERR].include?(io)
      io.close rescue nil
    end
  end

  # Make sure all input/output streams are closed
  # Part II: close all file decriptors (except for STDIN/STDOUT/STDERR)
  3.upto(8192) do |i|
    IO.for_fd(i).close rescue nil
  end
end

.daemonize(logfile_name = nil, app_name = nil) ⇒ Object

Transform the current process into a daemon


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# File 'lib/daemons/daemonize.rb', line 92

def daemonize(logfile_name = nil, app_name = nil)
  # Fork and exit from the parent
  safefork && exit

  # Detach from the controlling terminal
  unless sess_id = Process.setsid
    fail Daemons.RuntimeException.new('cannot detach from controlling terminal')
  end

  # Prevent the possibility of acquiring a controlling terminal
  trap 'SIGHUP', 'IGNORE'
  exit if pid = safefork

  $0 = app_name if app_name

  # Release old working directory
  Dir.chdir '/'

  close_io

  redirect_io(logfile_name)

  # Split rand streams between spawning and daemonized process
  srand

  sess_id
end

.redirect_io(logfile_name) ⇒ Object

Free STDIN/STDOUT/STDERR file descriptors and point them somewhere sensible


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# File 'lib/daemons/daemonize.rb', line 140

def redirect_io(logfile_name)
  begin; STDIN.reopen '/dev/null'; rescue ::Exception; end

  if logfile_name
    begin
      STDOUT.reopen logfile_name, 'a'
      File.chmod(0644, logfile_name)
      STDOUT.sync = true
    rescue ::Exception
      begin; STDOUT.reopen '/dev/null'; rescue ::Exception; end
    end
  else
    begin; STDOUT.reopen '/dev/null'; rescue ::Exception; end
  end

  begin; STDERR.reopen STDOUT; rescue ::Exception; end
  STDERR.sync = true
end

.safeforkObject

Try to fork if at all possible retrying every 5 sec if the maximum process limit for the system has been reached


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# File 'lib/daemons/daemonize.rb', line 4

def safefork
  tryagain = true

  while tryagain
    tryagain = false
    begin
      if pid = fork
        return pid
      end
    rescue Errno::EWOULDBLOCK
      sleep 5
      tryagain = true
    end
  end
end

.simulate(logfile_name = nil, app_name = nil) ⇒ Object

Simulate the daemonization process (:ontop mode) NOTE: STDOUT and STDERR will not be redirected to the logfile, because in :ontop mode, we normally want to see the output


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# File 'lib/daemons/daemonize.rb', line 24

def simulate(logfile_name = nil, app_name = nil)
  $0 = app_name if app_name

  # Release old working directory
  Dir.chdir '/'

  close_io

  # Free STDIN and point it to somewhere sensible
  begin; STDIN.reopen '/dev/null'; rescue ::Exception; end

  # Split rand streams between spawning and daemonized process
  srand
end