Use save_and_reraise_exception() from common.

This patch common.excutils from openstack-common, which includes
save_and_reraise_exception().  The patch also converts the code
base to use it from there instead of nova.utils and then removes
it from nova.utils.

The initial motivation for this was removing another nova dependency
from nova.rpc so that it can eventually be moved to openstack-common.

Change-Id: I7354ca51a02aec9c709cf33f77d4abc46acc2742

1 files changed, 49 insertions, 0 deletions

diff --git a/nova/openstack/common/excutils.py b/nova/openstack/common/excutils.py
new file mode 100644
index 000000000..3cb678e9d
--- /dev/null
+++ b/nova/openstack/common/excutils.py
@@ -0,0 +1,49 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# 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