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OpenStack Study: excutils.py

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# Copyright 2011 OpenStack Foundation.

# Copyright 2012, Red Hat, Inc.

#

# 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.

"""

Exception related utilities.

"""

import logging

import sys

import time

import traceback

import six

from nova.openstack.common.gettextutils import _ # noqa

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class save_and_reraise_exception(object):

"""Save current exception, run some code and then re-raise.

In some cases the exception context can be cleared, resulting in None

being attempted to be re-raised after an exception handler is run. This

can happen when eventlet switches greenthreads or when running an

exception handler, code raises and catches an exception. In both

cases the exception context will be cleared.

To work around this, we save the exception state, run handler code, and

then re-raise the original exception. If another exception occurs, the

saved exception is logged and the new exception is re-raised.

In some cases the caller may not want to re-raise the exception, and

for those circumstances this context provides a reraise flag that

can be used to suppress the exception. For example:

except Exception:

with save_and_reraise_exception() as ctxt:

decide_if_need_reraise()

if not should_be_reraised:

ctxt.reraise = False

"""

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    def __init__(self):

        self.reraise = True

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    def __enter__(self):

        self.type_, self.value, self.tb, = sys.exc_info()

        return self

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    def __exit__(self, exc_type, exc_val, exc_tb):

        if exc_type is not None:

            logging.error(_('Original exception being dropped: %s'),

                          traceback.format_exception(self.type_,

                                                     self.value,

                                                     self.tb))

            return False

        if self.reraise:

            six.reraise(self.type_, self.value, self.tb)

def forever_retry_uncaught_exceptions(infunc):

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def forever_retry_uncaught_exceptions(infunc):

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    def inner_func(*args, **kwargs):

        last_log_time = 0

        last_exc_message = None

        exc_count = 0

        while True:

            try:

                return infunc(*args, **kwargs)

            except Exception as exc:

                this_exc_message = six.u(str(exc))

                if this_exc_message == last_exc_message:

                    exc_count += 1

                else:

                    exc_count = 1

                # Do not log any more frequently than once a minute unless

                # the exception message changes

                cur_time = int(time.time())

                if (cur_time - last_log_time > 60 or

                        this_exc_message != last_exc_message):

                    logging.exception(

                        _('Unexpected exception occurred %d time(s)... '

                          'retrying.') % exc_count)

                    last_log_time = cur_time

                    last_exc_message = this_exc_message

                    exc_count = 0

                # This should be a very rare event. In case it isn't, do

                # a sleep.

                time.sleep(1)

    return inner_func