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, except_pass=None):
  11   '''Creates a Future which returns a list of results from each Future in
  12   |futures|. |except_pass| should be one or more exceptions to ignore when
  13   calling Get on the futures.
  14   '''
  15   def resolve():
  16     resolved = []
  17     for f in futures:
  18       try:
  19         resolved.append(f.Get())
  20       # "except None" will simply not catch any errors
  21       except except_pass:
  22         pass
  23     return resolved
  24   return Future(callback=resolve)
  25
  26
  27 class Future(object):
  28   '''Stores a value, error, or callback to be used later.
  29   '''
  30   def __init__(self, value=_no_value, callback=None, exc_info=None):
  31     self._value = value
  32     self._callback = callback
  33     self._exc_info = exc_info
  34     if (self._value is _no_value and
  35         self._callback is None and
  36         self._exc_info is None):
  37       raise ValueError('Must have either a value, error, or callback.')
  38
  39   def Get(self):
  40     '''Gets the stored value, error, or callback contents.
  41     '''
  42     if self._value is not _no_value:
  43       return self._value
  44     if self._exc_info is not None:
  45       self._Raise()
  46     try:
  47       self._value = self._callback()
  48       return self._value
  49     except:
  50       self._exc_info = sys.exc_info()
  51       self._Raise()
  52
  53   def _Raise(self):
  54     exc_info = self._exc_info
  55     raise exc_info[0], exc_info[1], exc_info[2]