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# Copyright 2011 OpenStack LLC.
# 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 contextlib
import logging
import sys
import traceback


@contextlib.contextmanager
def save_and_reraise_exception():
    """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 reraised 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 reraised.
    """
    type_, value, tb = sys.exc_info()
    try:
        yield
    except Exception:
        logging.error('Original exception being dropped: %s' %
                      (traceback.format_exception(type_, value, tb)))
        raise
    raise type_, value, tb
