Synnefo » snf-ganeti

#

#

# Copyright (C) 2006, 2007, 2008 Google Inc.

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful, but

# WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

# General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

# 02110-1301, USA.

"""Module with helper classes and functions for daemons"""

import select

import signal

import errno

from ganeti import utils

class Mainloop(object):

  """Generic mainloop for daemons

  """

  def __init__(self):

    self._io_wait = []

    self._signal_wait = []

    self.sigchld_handler = {}

  def Run(self):

    # TODO: Does not yet support adding new event sources while running

    poller = select.poll()

    for (owner, fd, conditions) in self._io_wait:

      poller.register(fd, conditions)

    self.sigchld_handler = utils.SignalHandler([signal.SIGCHLD])

    try:

      while True:

        try:

          io_events = poller.poll(1000)

        except select.error, err:

          # EINTR can happen when signals are sent

          if err.args and err.args[0] in (errno.EINTR,):

            io_events = None

          else:

            raise

        if io_events:

          # Check for I/O events

          for (evfd, evcond) in io_events:

            for (owner, fd, conditions) in self._io_wait:

              if fd == evfd and evcond & conditions:

                owner.OnIO(fd, evcond)

        # Check whether signal was raised

        if self.sigchld_handler.called:

          for owner in self._signal_wait:

            owner.OnSignal(signal.SIGCHLD)

          self.sigchld_handler.Clear()

    finally:

      self.sigchld_handler.Reset()

      self.sigchld_handler = None

  def RegisterIO(self, owner, fd, condition):

    """Registers a receiver for I/O notifications

    The receiver must support a "OnIO(self, fd, conditions)" function.

    @type owner: instance

    @param owner: Receiver

    @type fd: int

    @param fd: File descriptor

    @type condition: int

    @param condition: ORed field of conditions to be notified

                      (see select module)

    """

    self._io_wait.append((owner, fd, condition))

  def RegisterSignal(self, owner):

    """Registers a receiver for signal notifications

    The receiver must support a "OnSignal(self, signum)" function.

    @type owner: instance

    @param owner: Receiver

    """

    self._signal_wait.append(owner)