Module: EventedBluepill::System

Extended by:
System
Included in:
System
Defined in:
lib/evented_bluepill/system.rb

Overview

This class represents the system that evented_bluepill is running on.. It’s mainly used to memoize results of running ps auxx etc so that every watch in the every process will not result in a fork

Constant Summary collapse

APPEND_MODE = 
"a"
SECONDS_VALID = 
2
IDX_MAP =

The position of each field in ps output

{
  :pid => 0,
  :ppid => 1,
  :pcpu => 2,
  :rss => 3
}

Instance Method Summary collapse

Instance Method Details

#can_write_pid_file(pid_file, logger) ⇒ Object 



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# File 'lib/evented_bluepill/system.rb', line 186

def can_write_pid_file(pid_file, logger)
  FileUtils.touch(pid_file)
  File.unlink(pid_file)
  return true

rescue Exception => e
  logger.warning "%s - %s" % [e.class.name, e.message]
  e.backtrace.each {|l| logger.warning l}
  return false
end

#cpu_usage(pid) ⇒ Object 



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# File 'lib/evented_bluepill/system.rb', line 32

def cpu_usage(pid)
  ps_axu[pid] && ps_axu[pid][IDX_MAP[:pcpu]].to_f
end

#daemonize(cmd, options = {}) ⇒ Object

Returns the pid of the child that executes the cmd



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# File 'lib/evented_bluepill/system.rb', line 49

def daemonize(cmd, options = {})
  rd, wr = IO.pipe

  if child = Daemonize.safefork
    # we do not wanna create zombies, so detach ourselves from the child exit status
    ::Process.detach(child)

    # parent
    wr.close

    daemon_id = rd.read.to_i
    rd.close

    return daemon_id if daemon_id > 0

  else
    # child
    rd.close

    drop_privileges(options[:uid], options[:gid])

    # if we cannot write the pid file as the provided user, err out
    exit unless can_write_pid_file(options[:pid_file], options[:logger])

    to_daemonize = lambda do
      # Setting end PWD env emulates bash behavior when dealing with symlinks
      Dir.chdir(ENV["PWD"] = options[:working_dir]) if options[:working_dir]
      options[:environment].each { |key, value| ENV[key.to_s] = value.to_s } if options[:environment]

      redirect_io(*options.values_at(:stdin, :stdout, :stderr))

      ::Kernel.exec(*Shellwords.shellwords(cmd))
      exit
    end

    daemon_id = Daemonize.call_as_daemon(to_daemonize, nil, cmd)

    File.open(options[:pid_file], "w") {|f| f.write(daemon_id)}

    wr.write daemon_id
    wr.close

    exit
  end
end

#drop_privileges(uid, gid) ⇒ Object

be sure to call this from a fork otherwise it will modify the attributes of the evented_bluepill daemon



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# File 'lib/evented_bluepill/system.rb', line 175

def drop_privileges(uid, gid)
  if ::Process::Sys.geteuid == 0
    uid_num = Etc.getpwnam(uid).uid if uid
    gid_num = Etc.getgrnam(gid).gid if gid

    ::Process.groups = [gid_num] if gid
    ::Process::Sys.setgid(gid_num) if gid
    ::Process::Sys.setuid(uid_num) if uid
  end
end

#execute_blocking(cmd, options = {}) ⇒ Object

Returns the stdout, stderr and exit code of the cmd



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# File 'lib/evented_bluepill/system.rb', line 96

def execute_blocking(cmd, options = {})
  rd, wr = IO.pipe

  if child = Daemonize.safefork
    # parent
    wr.close

    cmd_status = rd.read
    rd.close

    ::Process.waitpid(child)

    return Marshal.load(cmd_status)

  else
    # child
    rd.close

    # create a child in which we can override the stdin, stdout and stderr
    cmd_out_read, cmd_out_write = IO.pipe
    cmd_err_read, cmd_err_write = IO.pipe

    pid = fork {
      # grandchild
      drop_privileges(options[:uid], options[:gid])

      Dir.chdir(ENV["PWD"] = options[:working_dir]) if options[:working_dir]
      options[:environment].each { |key, value| ENV[key.to_s] = value.to_s } if options[:environment]

      # close unused fds so ancestors wont hang. This line is the only reason we are not
      # using something like popen3. If this fd is not closed, the .read call on the parent
      # will never return because "wr" would still be open in the "exec"-ed cmd
      wr.close

      # we do not care about stdin of cmd
      STDIN.reopen("/dev/null")

      # point stdout of cmd to somewhere we can read
      cmd_out_read.close
      STDOUT.reopen(cmd_out_write)
      cmd_out_write.close

      # same thing for stderr
      cmd_err_read.close
      STDERR.reopen(cmd_err_write)
      cmd_err_write.close

      # finally, replace grandchild with cmd
      ::Kernel.exec(*Shellwords.shellwords(cmd))
    }

    # we do not use these ends of the pipes in the child
    cmd_out_write.close
    cmd_err_write.close

    # wait for the cmd to finish executing and acknowledge it's death
    ::Process.waitpid(pid)

    # collect stdout, stderr and exitcode
    result = {
      :stdout => cmd_out_read.read,
      :stderr => cmd_err_read.read,
      :exit_code => $?.exitstatus
    }

    # We're done with these ends of the pipes as well
    cmd_out_read.close
    cmd_err_read.close

    # Time to tell the parent about what went down
    wr.write Marshal.dump(result)
    wr.close

    exit
  end
end

#get_children(parent_pid) ⇒ Object 



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# File 'lib/evented_bluepill/system.rb', line 40

def get_children(parent_pid)
  child_pids = Array.new
  ps_axu.each_pair do |pid, chunks|
    child_pids << chunks[IDX_MAP[:pid]].to_i if chunks[IDX_MAP[:ppid]].to_i == parent_pid.to_i
  end
  child_pids
end

#memory_usage(pid) ⇒ Object 



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# File 'lib/evented_bluepill/system.rb', line 36

def memory_usage(pid)
  ps_axu[pid] && ps_axu[pid][IDX_MAP[:rss]].to_f
end

#pid_alive?(pid) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/evented_bluepill/system.rb', line 23

def pid_alive?(pid)
  begin
    ::Process.kill(0, pid)
    true
  rescue Errno::ESRCH
    false
  end
end

#redirect_io(io_in, io_out, io_err) ⇒ Object 



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# File 'lib/evented_bluepill/system.rb', line 197

def redirect_io(io_in, io_out, io_err)
  $stdin.reopen(io_in) if io_in

  if !io_out.nil? && !io_err.nil? && io_out == io_err
    $stdout.reopen(io_out, APPEND_MODE)
    $stderr.reopen($stdout)

  else
    $stdout.reopen(io_out, APPEND_MODE) if io_out
    $stderr.reopen(io_err, APPEND_MODE) if io_err
  end
end