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#
# Copyright (C) 2009-2016 CEA/DAM
# Copyright (C) 2016 Stephane Thiell <sthiell@stanford.edu>
#
# This file is part of ClusterShell.
#
# ClusterShell is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# ClusterShell 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
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with ClusterShell; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
"""
Engine Factory to select the best working event engine for the current
version of Python and Operating System.
"""
import logging
from ClusterShell.Engine.Engine import EngineNotSupportedError
# Available event engines
from ClusterShell.Engine.EPoll import EngineEPoll
from ClusterShell.Engine.Poll import EnginePoll
from ClusterShell.Engine.Select import EngineSelect
class PreferredEngine(object):
"""
Preferred Engine selection metaclass (DP Abstract Factory).
"""
engines = {EngineEPoll.identifier: EngineEPoll,
EnginePoll.identifier: EnginePoll,
EngineSelect.identifier: EngineSelect}
def __new__(cls, hint, info):
"""
Create a new preferred Engine.
"""
if not hint or hint == 'auto':
# in order or preference
for engine_class in [EngineEPoll, EnginePoll, EngineSelect]:
try:
return engine_class(info)
except EngineNotSupportedError:
pass
raise RuntimeError("FATAL: No supported ClusterShell.Engine found")
else:
# User overriding engine selection
engines = cls.engines.copy()
try:
tryengine = engines.pop(hint)
while True:
try:
return tryengine(info)
except EngineNotSupportedError:
if len(engines) == 0:
raise
tryengine = engines.popitem()[1]
except KeyError:
msg = "Invalid engine identifier: %s" % hint
logging.getLogger(__name__).error(msg)
raise
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