Source Code for Module ClusterShell.Engine.Factory

 1  # 
 2  # Copyright (C) 2009-2016 CEA/DAM 
 3  # Copyright (C) 2016 Stephane Thiell <sthiell@stanford.edu> 
 4  # 
 5  # This file is part of ClusterShell. 
 6  # 
 7  # ClusterShell is free software; you can redistribute it and/or 
 8  # modify it under the terms of the GNU Lesser General Public 
 9  # License as published by the Free Software Foundation; either 
10  # version 2.1 of the License, or (at your option) any later version. 
11  # 
12  # ClusterShell is distributed in the hope that it will be useful, 
13  # but WITHOUT ANY WARRANTY; without even the implied warranty of 
14  # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU 
15  # Lesser General Public License for more details. 
16  # 
17  # You should have received a copy of the GNU Lesser General Public 
18  # License along with ClusterShell; if not, write to the Free Software 
19  # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 
20   
21  """ 
22  Engine Factory to select the best working event engine for the current 
23  version of Python and Operating System. 
24  """ 
25   
26  import logging 
27   
28  from ClusterShell.Engine.Engine import EngineNotSupportedError 
29   
30  # Available event engines 
31  from ClusterShell.Engine.EPoll import EngineEPoll 
32  from ClusterShell.Engine.Poll import EnginePoll 
33  from ClusterShell.Engine.Select import EngineSelect 
34   
35   
36 -class PreferredEngine(object): 
37      """ 
38      Preferred Engine selection metaclass (DP Abstract Factory). 
39      """ 
40   
41      engines = {EngineEPoll.identifier: EngineEPoll, 
42                 EnginePoll.identifier: EnginePoll, 
43                 EngineSelect.identifier: EngineSelect} 
44   
45 -    def __new__(cls, hint, info): 
46          """ 
47          Create a new preferred Engine. 
48          """ 
49          if not hint or hint == 'auto': 
50              # in order or preference 
51              for engine_class in [EngineEPoll, EnginePoll, EngineSelect]: 
52                  try: 
53                      return engine_class(info) 
54                  except EngineNotSupportedError: 
55                      pass 
56              raise RuntimeError("FATAL: No supported ClusterShell.Engine found") 
57          else: 
58              # User overriding engine selection 
59              engines = cls.engines.copy() 
60              try: 
61                  tryengine = engines.pop(hint) 
62                  while True: 
63                      try: 
64                          return tryengine(info) 
65                      except EngineNotSupportedError: 
66                          if len(engines) == 0: 
67                              raise 
68                      tryengine = engines.popitem()[1] 
69              except KeyError: 
70                  msg = "Invalid engine identifier: %s" % hint 
71                  logging.getLogger(__name__).error(msg) 
72                  raise 
73