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# Copyright (c) 2012 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
import sys
_no_value = object()
def Collect(futures):
'''Creates a Future which returns a list of results from each Future in
|futures|.
'''
return Future(delegate=Gettable(lambda: [f.Get() for f in futures]))
class Gettable(object):
'''Allows a Future to accept a callable as a delegate. Wraps |f| in a .Get
interface required by Future.
'''
def __init__(self, f, *args):
self._g = lambda: f(*args)
def Get(self):
return self._g()
class Future(object):
'''Stores a value, error, or delegate to be used later.
'''
def __init__(self, value=_no_value, delegate=None, exc_info=None):
self._value = value
self._delegate = delegate
self._exc_info = exc_info
if (self._value is _no_value and
self._delegate is None and
self._exc_info is None):
raise ValueError('Must have either a value, error, or delegate.')
def Get(self):
'''Gets the stored value, error, or delegate contents.
'''
if self._value is not _no_value:
return self._value
if self._exc_info is not None:
self._Raise()
try:
self._value = self._delegate.Get()
return self._value
except:
self._exc_info = sys.exc_info()
self._Raise()
def _Raise(self):
exc_info = self._exc_info
raise exc_info[0], exc_info[1], exc_info[2]
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