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#
# Copyright Red Hat
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA.
#
"""
Transaction - provides transactional support
$Id: //eng/vdo-releases/aluminum/src/python/vdo/utils/Transaction.py#1 $
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals
from functools import wraps
import gettext
import sys
import threading
gettext.install('Transaction')
#####################################################################
if (sys.version_info > (3, 0)):
def reraise(ex, val, tb):
#pylint: disable=E0710
raise ex.with_traceback(tb)
else:
exec("""def reraise(ex, val, tb):
raise type(ex), val, tb
""")
class Transaction(object):
"""Client-visible transaction object.
"""
# A dictionary mapping thread identifier to a list of the thread's
# transactions.
__transactionLists = {}
######################################################################
# Public methods
######################################################################
@classmethod
def transaction(cls):
"""Returns the current transaction for the current thread.
"""
return cls._threadTransactionList()[-1]
######################################################################
def addUndoStage(self, undoStage):
"""Adds callable undoStage to transaction stages.
Arguments:
undoStage (callable) - callable to execute as part of
transaction roll-back
"""
self.__undoStages.append(undoStage)
######################################################################
def setMessage(self, handleMessage, message = None):
"""Sets the message to handle if there is an exception.
If message is specified and an exception occurs the exception
will be appended to the message using "; {0}" where "{0}" represents
the exception.
If message is not specified, the exception will be coerced to
a string and passed to handleMessage.
Specifying handleMessage as None will clear both handleMessage and
message.
Arguments:
handleMessage (callable) - method to handle message
message (string) - message
"""
raise NotImplementedError
######################################################################
# Overridden methods
######################################################################
def __init__(self):
super(Transaction, self).__init__()
self.__undoStages = []
######################################################################
# Protected methods
######################################################################
@classmethod
def _threadTransactionList(cls):
"""Returns the transaction list for the current thread, creating it
if need be.
Returns:
list of Transactions
"""
transactionList = None
threadId = threading.currentThread().ident
try:
transactionList = cls.__transactionLists[threadId]
except KeyError:
transactionList = []
cls.__transactionLists[threadId] = transactionList
return transactionList
######################################################################
def _undoStages(self):
"""Returns the list of undo stages for the transaction.
Returns:
list of undo stages
"""
return self.__undoStages
######################################################################
# Private methods
######################################################################
########################################################################
def transactional(func):
"""Method decorator providing transactional capabilities to the method.
"""
######################################################################
class _Transaction(Transaction):
"""Decorator-local transaction object providing actual transaction
capabilities.
"""
####################################################################
# Public methods
####################################################################
@classmethod
def addTransaction(cls):
"""Adds, and returns, a transaction to the transaction list for the
current thread.
"""
cls._threadTransactionList().append(cls())
return cls.transaction()
####################################################################
@classmethod
def removeTransaction(cls):
"""Removes the current transaction for for the current thread.
"""
cls._threadTransactionList().pop()
####################################################################
def undo(self, exception):
"""Performs the undo processing of the transaction.
Exceptions from the undo stages are ignored.
Arguments:
exception - the exception which resulted in undo being called
"""
# Handle any message that was set for the transaction.
if self.__handleMessage is not None:
if self.__message is not None:
self.__handleMessage(_("{0}; {1}").format(self.__message,
str(exception)))
else:
self.__handleMessage(str(exception))
# Perform the undo processing.
undoStages = self._undoStages()[:]
undoStages.reverse()
for undoStage in undoStages:
try:
undoStage()
except Exception:
pass
####################################################################
# Overridden methods
####################################################################
def __init__(self):
super(_Transaction, self).__init__()
self.__handleMessage = None
self.__message = None
####################################################################
def setMessage(self, handleMessage, message = None):
self.__handleMessage = handleMessage
if self.__handleMessage is None:
self.__message = None
else:
self.__message = message
####################################################################
# Protected methods
####################################################################
####################################################################
# Private methods
####################################################################
######################################################################
@wraps(func)
def wrap(*args, **kwargs):
"""Wrapper method providing transactional processing capabilities.
"""
transaction = _Transaction.addTransaction()
result = None
try:
result = func(*args, **kwargs)
except Exception as ex:
transaction.undo(ex)
reraise(ex, ex, sys.exc_info()[2])
finally:
_Transaction.removeTransaction()
return result
return wrap
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