text: # Copyright (c) 2013 Rackspace Hosting
  # All Rights Reserved.
  #
  #    Licensed under the Apache License, Version 2.0 (the "License"); you may
  #    not use this file except in compliance with the License. You may obtain
  #    a copy of the License at
  #
  #         http://www.apache.org/licenses/LICENSE-2.0
  #
  #    Unless required by applicable law or agreed to in writing, software
  #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  #    License for the specific language governing permissions and limitations
  #    under the License.
  
  """
  =================================
  Multiple DB API backend support.
  =================================
  
  A DB backend module should implement a method named 'get_backend' which
  takes no arguments. The method can return any object that implements DB
  API methods.
  """
  
  import logging
  import random
  import threading
  import time
  
  from debtcollector import removals
  from oslo_utils import excutils
  from oslo_utils import importutils
  from oslo_utils import reflection
  import six
  
  from oslo_db import exception
  from oslo_db import options
  
  
  LOG = logging.getLogger(__name__)
  
  
  def safe_for_db_retry(f):
      """Indicate api method as safe for re-connection to database.
  
      Database connection retries will be enabled for the decorated api method.
      Database connection failure can have many causes, which can be temporary.
      In such cases retry may increase the likelihood of connection.
  
      Usage::
  
          @safe_for_db_retry
          def api_method(self):
              self.engine.connect()
  
  
      :param f: database api method.
      :type f: function.
      """
      f.__dict__['enable_retry_on_disconnect'] = True
      return f
  
  
  def retry_on_deadlock(f):
      """Retry a DB API call if Deadlock was received.
  
      wrap_db_entry will be applied to all db.api functions marked with this
      decorator.
      """
      f.__dict__['enable_retry_on_deadlock'] = True
      return f
  
  
  def retry_on_request(f):
      """Retry a DB API call if RetryRequest exception was received.
  
      wrap_db_entry will be applied to all db.api functions marked with this
      decorator.
      """
      f.__dict__['enable_retry_on_request'] = True
      return f
  
  
  class wrap_db_retry(object):
      """Retry db.api methods, if db_error raised
  
      Retry decorated db.api methods. This decorator catches db_error and retries
      function in a loop until it succeeds, or until maximum retries count
      will be reached.
  
      Keyword arguments:
  
      :param retry_interval: seconds between transaction retries
      :type retry_interval: int or float
  
      :param max_retries: max number of retries before an error is raised
      :type max_retries: int
  
      :param inc_retry_interval: determine increase retry interval or not
      :type inc_retry_interval: bool
  
      :param max_retry_interval: max interval value between retries
      :type max_retry_interval: int or float
  
      :param exception_checker: checks if an exception should trigger a retry
      :type exception_checker: callable
  
      :param jitter: determine increase retry interval use jitter or not, jitter
             is always interpreted as True for a DBDeadlockError
      :type jitter: bool
      """
  
      @removals.removed_kwarg("retry_on_request",
                              "Retry on request is always enabled")
      def __init__(self, retry_interval=1, max_retries=20,
                   inc_retry_interval=True,
                   max_retry_interval=10, retry_on_disconnect=False,
                   retry_on_deadlock=False,
                   exception_checker=lambda exc: False,
                   jitter=False):
          super(wrap_db_retry, self).__init__()
  
          self.jitter = jitter
          self.db_error = (exception.RetryRequest, )
          # default is that we re-raise anything unexpected
          self.exception_checker = exception_checker
          if retry_on_disconnect:
              self.db_error += (exception.DBConnectionError, )
          if retry_on_deadlock:
              self.db_error += (exception.DBDeadlock, )
          self.retry_interval = retry_interval
          self.max_retries = max_retries
          self.inc_retry_interval = inc_retry_interval
          self.max_retry_interval = max_retry_interval
  
      def __call__(self, f):
          @six.wraps(f)
          def wrapper(*args, **kwargs):
              sleep_time = next_interval = self.retry_interval
              remaining = self.max_retries
  
              while True:
                  try:
                      return f(*args, **kwargs)
                  except Exception as e:
                      with excutils.save_and_reraise_exception() as ectxt:
                          expected = self._is_exception_expected(e)
                          if remaining > 0:
                              ectxt.reraise = not expected
                          else:
                              if expected:
                                  LOG.exception('DB exceeded retry limit.')
                              # if it's a RetryRequest, we need to unpack it
                              if isinstance(e, exception.RetryRequest):
                                  ectxt.type_ = type(e.inner_exc)
                                  ectxt.value = e.inner_exc
                      LOG.debug("Performing DB retry for function %s",
                                reflection.get_callable_name(f))
                      # NOTE(vsergeyev): We are using patched time module, so
                      #                  this effectively yields the execution
                      #                  context to another green thread.
                      time.sleep(sleep_time)
                      if self.inc_retry_interval:
                          # NOTE(jiangyikun): In order to minimize the chance of
                          # regenerating a deadlock and reduce the average sleep
                          # time, we are using jitter by default when the
                          # deadlock is detected. With the jitter,
                          # sleep_time = [0, next_interval), otherwise, without
                          # the jitter, sleep_time = next_interval.
                          if isinstance(e, exception.DBDeadlock):
                              jitter = True
                          else:
                              jitter = self.jitter
                          sleep_time, next_interval = self._get_inc_interval(
                              next_interval, jitter)
                      remaining -= 1
  
          return wrapper
  
      def _is_exception_expected(self, exc):
          if isinstance(exc, self.db_error):
              # RetryRequest is application-initated exception
              # and not an error condition in case retries are
              # not exceeded
              if not isinstance(exc, exception.RetryRequest):
                  LOG.debug('DB error: %s', exc)
              return True
          return self.exception_checker(exc)
  
      def _get_inc_interval(self, n, jitter):
          # NOTE(jiangyikun): The "n" help us to record the 2 ** retry_times.
          # The "sleep_time" means the real time to sleep:
          # - Without jitter: sleep_time = 2 ** retry_times = n
          # - With jitter:    sleep_time = [0, 2 ** retry_times) < n
          n = n * 2
          if jitter:
              sleep_time = random.uniform(0, n)
          else:
              sleep_time = n
          return min(sleep_time, self.max_retry_interval), n
  
  
  class DBAPI(object):
      """Initialize the chosen DB API backend.
  
      After initialization API methods is available as normal attributes of
      ``DBAPI`` subclass. Database API methods are supposed to be called as
      DBAPI instance methods.
  
      :param backend_name: name of the backend to load
      :type backend_name: str
  
      :param backend_mapping: backend name -> module/class to load mapping
      :type backend_mapping: dict
      :default backend_mapping: None
  
      :param lazy: load the DB backend lazily on the first DB API method call
      :type lazy: bool
      :default lazy: False
  
      :keyword use_db_reconnect: retry DB transactions on disconnect or not
      :type use_db_reconnect: bool
  
      :keyword retry_interval: seconds between transaction retries
      :type retry_interval: int
  
      :keyword inc_retry_interval: increase retry interval or not
      :type inc_retry_interval: bool
  
      :keyword max_retry_interval: max interval value between retries
      :type max_retry_interval: int
  
      :keyword max_retries: max number of retries before an error is raised
      :type max_retries: int
      """
  
      def __init__(self, backend_name, backend_mapping=None, lazy=False,
                   **kwargs):
  
          self._backend = None
          self._backend_name = backend_name
          self._backend_mapping = backend_mapping or {}
          self._lock = threading.Lock()
  
          if not lazy:
              self._load_backend()
  
          self.use_db_reconnect = kwargs.get('use_db_reconnect', False)
          self._wrap_db_kwargs = {k: v for k, v in kwargs.items()
                                  if k in ('retry_interval',
                                           'inc_retry_interval',
                                           'max_retry_interval',
                                           'max_retries')}
  
      def _load_backend(self):
          with self._lock:
              if not self._backend:
                  # Import the untranslated name if we don't have a mapping
                  backend_path = self._backend_mapping.get(self._backend_name,
                                                           self._backend_name)
                  LOG.debug('Loading backend %(name)r from %(path)r',
                            {'name': self._backend_name,
                             'path': backend_path})
                  backend_mod = importutils.import_module(backend_path)
                  self._backend = backend_mod.get_backend()
  
      def __getattr__(self, key):
          if not self._backend:
              self._load_backend()
  
          attr = getattr(self._backend, key)
          if not hasattr(attr, '__call__'):
              return attr
          # NOTE(vsergeyev): If `use_db_reconnect` option is set to True, retry
          #                  DB API methods, decorated with @safe_for_db_retry
          #                  on disconnect.
          retry_on_disconnect = self.use_db_reconnect and attr.__dict__.get(
              'enable_retry_on_disconnect', False)
          retry_on_deadlock = attr.__dict__.get('enable_retry_on_deadlock',
                                                False)
          retry_on_request = attr.__dict__.get('enable_retry_on_request', False)
  
          if retry_on_disconnect or retry_on_deadlock or retry_on_request:
              attr = wrap_db_retry(
                  retry_on_disconnect=retry_on_disconnect,
                  retry_on_deadlock=retry_on_deadlock,
                  **self._wrap_db_kwargs)(attr)
  
          return attr
  
      @classmethod
      def from_config(cls, conf, backend_mapping=None, lazy=False):
          """Initialize DBAPI instance given a config instance.
  
          :param conf: oslo.config config instance
          :type conf: oslo.config.cfg.ConfigOpts
  
          :param backend_mapping: backend name -> module/class to load mapping
          :type backend_mapping: dict
  
          :param lazy: load the DB backend lazily on the first DB API method call
          :type lazy: bool
  
          """
  
          conf.register_opts(options.database_opts, 'database')
  
          return cls(backend_name=conf.database.backend,
                     backend_mapping=backend_mapping,
                     lazy=lazy,
                     use_db_reconnect=conf.database.use_db_reconnect,
                     retry_interval=conf.database.db_retry_interval,
                     inc_retry_interval=conf.database.db_inc_retry_interval,
                     max_retry_interval=conf.database.db_max_retry_interval,
                     max_retries=conf.database.db_max_retries)
  