chrome/common/extensions/docs/server2/future.py

   1 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 # Use of this source code is governed by a BSD-style license that can be
   3 # found in the LICENSE file.
   4
   5 import sys
   6
   7 _no_value = object()
   8
   9
  10 def Collect(futures):
  11   '''Creates a Future which returns a list of results from each Future in
  12   |futures|.
  13   '''
  14   return Future(callback=lambda: [f.Get() for f in futures])
  15
  16
  17 class Future(object):
  18   '''Stores a value, error, or callback to be used later.
  19   '''
  20   def __init__(self, value=_no_value, callback=None, exc_info=None):
  21     self._value = value
  22     self._callback = callback
  23     self._exc_info = exc_info
  24     if (self._value is _no_value and
  25         self._callback is None and
  26         self._exc_info is None):
  27       raise ValueError('Must have either a value, error, or callback.')
  28
  29   def Get(self):
  30     '''Gets the stored value, error, or callback contents.
  31     '''
  32     if self._value is not _no_value:
  33       return self._value
  34     if self._exc_info is not None:
  35       self._Raise()
  36     try:
  37       self._value = self._callback()
  38       return self._value
  39     except:
  40       self._exc_info = sys.exc_info()
  41       self._Raise()
  42
  43   def _Raise(self):
  44     exc_info = self._exc_info
  45     raise exc_info[0], exc_info[1], exc_info[2]