indico/util/caching.py

   1 # This file is part of Indico.
   2 # Copyright (C) 2002 - 2015 European Organization for Nuclear Research (CERN).
   3 #
   4 # Indico is free software; you can redistribute it and/or
   5 # modify it under the terms of the GNU General Public License as
   6 # published by the Free Software Foundation; either version 3 of the
   7 # License, or (at your option) any later version.
   8 #
   9 # Indico is distributed in the hope that it will be useful, but
  10 # WITHOUT ANY WARRANTY; without even the implied warranty of
  11 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 # General Public License for more details.
  13 #
  14 # You should have received a copy of the GNU General Public License
  15 # along with Indico; if not, see <http://www.gnu.org/licenses/>.
  16
  17 from functools import wraps
  18
  19 from flask import has_request_context, g, current_app
  20
  21
  22 def make_hashable(obj):
  23     if isinstance(obj, list):
  24         return tuple(obj)
  25     elif isinstance(obj, dict):
  26         return frozenset((k, make_hashable(v)) for k, v in obj.iteritems())
  27     elif hasattr(obj, 'getId'):
  28         return obj.__class__.__name__, obj.getId()
  29     return obj
  30
  31
  32 # http://wiki.python.org/moin/PythonDecoratorLibrary#Alternate_memoize_as_nested_functions
  33 # Not thread-safe. Don't use it in places where thread-safety is important!
  34 def memoize(obj):
  35     cache = {}
  36
  37     @wraps(obj)
  38     def memoizer(*args, **kwargs):
  39         key = (make_hashable(args), make_hashable(kwargs))
  40         if key not in cache:
  41             cache[key] = obj(*args, **kwargs)
  42         return cache[key]
  43     return memoizer
  44
  45
  46 def memoize_request(f):
  47     """Memoizes a function during the current request"""
  48     @wraps(f)
  49     def memoizer(*args, **kwargs):
  50         if not has_request_context() or current_app.config['TESTING']:
  51             # No memoization outside request context
  52             return f(*args, **kwargs)
  53
  54         try:
  55             cache = g.memoize_cache
  56         except AttributeError:
  57             g.memoize_cache = cache = {}
  58
  59         key = (f.__name__, make_hashable(args), make_hashable(kwargs))
  60         if key not in cache:
  61             cache[key] = f(*args, **kwargs)
  62         return cache[key]
  63
  64     return memoizer