lib/config/utils.py

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# Copyright (C) 2014 Google Inc.
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"""Utilities used by the config module."""


import logging


def ConfigSync(shared=0):
  """Configuration synchronization decorator.

  """
  def wrap(fn):
    def sync_function(*args, **kwargs):
      with args[0].GetConfigManager(shared):
        return fn(*args, **kwargs)
    return sync_function
  return wrap


class ConfigManager(object):
  """Locks the configuration and exposes it to be read or modified.

  """
  def __init__(self, config_writer, shared=False, forcelock=False):
    assert hasattr(config_writer, '_ConfigData'), \
           "invalid argument: Not a ConfigWriter"
    self._config_writer = config_writer
    self._shared = shared
    self._forcelock = forcelock

  def __enter__(self):
    try:
      self._config_writer._OpenConfig(# pylint: disable=W0212
                                      self._shared,
                                      force=self._forcelock)
    except Exception:
      logging.debug("Opening configuration failed")
      try:
        self._config_writer._CloseConfig(False) # pylint: disable=W0212
      except Exception: # pylint: disable=W0703
        logging.debug("Closing configuration failed as well")
      raise

  def __exit__(self, exc_type, exc_value, traceback):
    # save the configuration, if this was a write opreration that succeeded
    if exc_type is not None:
      logging.debug("Configuration operation failed,"
                    " the changes will not be saved")
    # pylint: disable=W0212
    self._config_writer._CloseConfig(not self._shared and exc_type is None)
    return False