Package cherrypy :: Module _cpthreadinglocal
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Source Code for Module cherrypy._cpthreadinglocal

  1  # This is a backport of Python-2.4's threading.local() implementation 
  2   
  3  """Thread-local objects 
  4   
  5  (Note that this module provides a Python version of thread 
  6   threading.local class.  Depending on the version of Python you're 
  7   using, there may be a faster one available.  You should always import 
  8   the local class from threading.) 
  9   
 10  Thread-local objects support the management of thread-local data. 
 11  If you have data that you want to be local to a thread, simply create 
 12  a thread-local object and use its attributes: 
 13   
 14    >>> mydata = local() 
 15    >>> mydata.number = 42 
 16    >>> mydata.number 
 17    42 
 18   
 19  You can also access the local-object's dictionary: 
 20   
 21    >>> mydata.__dict__ 
 22    {'number': 42} 
 23    >>> mydata.__dict__.setdefault('widgets', []) 
 24    [] 
 25    >>> mydata.widgets 
 26    [] 
 27   
 28  What's important about thread-local objects is that their data are 
 29  local to a thread. If we access the data in a different thread: 
 30   
 31    >>> log = [] 
 32    >>> def f(): 
 33    ...     items = mydata.__dict__.items() 
 34    ...     items.sort() 
 35    ...     log.append(items) 
 36    ...     mydata.number = 11 
 37    ...     log.append(mydata.number) 
 38   
 39    >>> import threading 
 40    >>> thread = threading.Thread(target=f) 
 41    >>> thread.start() 
 42    >>> thread.join() 
 43    >>> log 
 44    [[], 11] 
 45   
 46  we get different data.  Furthermore, changes made in the other thread 
 47  don't affect data seen in this thread: 
 48   
 49    >>> mydata.number 
 50    42 
 51   
 52  Of course, values you get from a local object, including a __dict__ 
 53  attribute, are for whatever thread was current at the time the 
 54  attribute was read.  For that reason, you generally don't want to save 
 55  these values across threads, as they apply only to the thread they 
 56  came from. 
 57   
 58  You can create custom local objects by subclassing the local class: 
 59   
 60    >>> class MyLocal(local): 
 61    ...     number = 2 
 62    ...     initialized = False 
 63    ...     def __init__(self, **kw): 
 64    ...         if self.initialized: 
 65    ...             raise SystemError('__init__ called too many times') 
 66    ...         self.initialized = True 
 67    ...         self.__dict__.update(kw) 
 68    ...     def squared(self): 
 69    ...         return self.number ** 2 
 70   
 71  This can be useful to support default values, methods and 
 72  initialization.  Note that if you define an __init__ method, it will be 
 73  called each time the local object is used in a separate thread.  This 
 74  is necessary to initialize each thread's dictionary. 
 75   
 76  Now if we create a local object: 
 77   
 78    >>> mydata = MyLocal(color='red') 
 79   
 80  Now we have a default number: 
 81   
 82    >>> mydata.number 
 83    2 
 84   
 85  an initial color: 
 86   
 87    >>> mydata.color 
 88    'red' 
 89    >>> del mydata.color 
 90   
 91  And a method that operates on the data: 
 92   
 93    >>> mydata.squared() 
 94    4 
 95   
 96  As before, we can access the data in a separate thread: 
 97   
 98    >>> log = [] 
 99    >>> thread = threading.Thread(target=f) 
100    >>> thread.start() 
101    >>> thread.join() 
102    >>> log 
103    [[('color', 'red'), ('initialized', True)], 11] 
104   
105  without affecting this thread's data: 
106   
107    >>> mydata.number 
108    2 
109    >>> mydata.color 
110    Traceback (most recent call last): 
111    ... 
112    AttributeError: 'MyLocal' object has no attribute 'color' 
113   
114  Note that subclasses can define slots, but they are not thread 
115  local. They are shared across threads: 
116   
117    >>> class MyLocal(local): 
118    ...     __slots__ = 'number' 
119   
120    >>> mydata = MyLocal() 
121    >>> mydata.number = 42 
122    >>> mydata.color = 'red' 
123   
124  So, the separate thread: 
125   
126    >>> thread = threading.Thread(target=f) 
127    >>> thread.start() 
128    >>> thread.join() 
129   
130  affects what we see: 
131   
132    >>> mydata.number 
133    11 
134   
135  >>> del mydata 
136  """ 
137   
138  # Threading import is at end 
139   
140 -class _localbase(object):
141 __slots__ = '_local__key', '_local__args', '_local__lock' 142
143 - def __new__(cls, *args, **kw):
144 self = object.__new__(cls) 145 key = 'thread.local.' + str(id(self)) 146 object.__setattr__(self, '_local__key', key) 147 object.__setattr__(self, '_local__args', (args, kw)) 148 object.__setattr__(self, '_local__lock', RLock()) 149 150 if args or kw and (cls.__init__ is object.__init__): 151 raise TypeError("Initialization arguments are not supported") 152 153 # We need to create the thread dict in anticipation of 154 # __init__ being called, to make sure we don't call it 155 # again ourselves. 156 dict = object.__getattribute__(self, '__dict__') 157 currentThread().__dict__[key] = dict 158 159 return self
160
161 -def _patch(self):
162 key = object.__getattribute__(self, '_local__key') 163 d = currentThread().__dict__.get(key) 164 if d is None: 165 d = {} 166 currentThread().__dict__[key] = d 167 object.__setattr__(self, '__dict__', d) 168 169 # we have a new instance dict, so call out __init__ if we have 170 # one 171 cls = type(self) 172 if cls.__init__ is not object.__init__: 173 args, kw = object.__getattribute__(self, '_local__args') 174 cls.__init__(self, *args, **kw) 175 else: 176 object.__setattr__(self, '__dict__', d)
177
178 -class local(_localbase):
179
180 - def __getattribute__(self, name):
181 lock = object.__getattribute__(self, '_local__lock') 182 lock.acquire() 183 try: 184 _patch(self) 185 return object.__getattribute__(self, name) 186 finally: 187 lock.release()
188
189 - def __setattr__(self, name, value):
190 lock = object.__getattribute__(self, '_local__lock') 191 lock.acquire() 192 try: 193 _patch(self) 194 return object.__setattr__(self, name, value) 195 finally: 196 lock.release()
197
198 - def __delattr__(self, name):
199 lock = object.__getattribute__(self, '_local__lock') 200 lock.acquire() 201 try: 202 _patch(self) 203 return object.__delattr__(self, name) 204 finally: 205 lock.release()
206 207
208 - def __del__():
209 threading_enumerate = enumerate 210 __getattribute__ = object.__getattribute__ 211 212 def __del__(self): 213 key = __getattribute__(self, '_local__key') 214 215 try: 216 threads = list(threading_enumerate()) 217 except: 218 # if enumerate fails, as it seems to do during 219 # shutdown, we'll skip cleanup under the assumption 220 # that there is nothing to clean up 221 return 222 223 for thread in threads: 224 try: 225 __dict__ = thread.__dict__ 226 except AttributeError: 227 # Thread is dying, rest in peace 228 continue 229 230 if key in __dict__: 231 try: 232 del __dict__[key] 233 except KeyError: 234 pass # didn't have anything in this thread
235 236 return __del__
237 __del__ = __del__() 238 239 from threading import currentThread, enumerate, RLock 240